Context.—

Distinction of hydatidiform moles from nonmolar specimens and subclassification of hydatidiform moles as complete hydatidiform mole versus partial hydatidiform mole are important for clinical practice and investigational studies. Risk of persistent gestational trophoblastic disease and clinical management differ for these entities. Diagnosis based on morphology is subject to interobserver variability and remains problematic, even for experienced gynecologic pathologists.

Objectives.—

To explain how ancillary techniques target the unique genetic features of hydatidiform moles to establish diagnostic truth, highlight the issue of diagnostic reproducibility and importance of diagnostic accuracy, and illustrate use of p57 immunohistochemistry and polymerase chain reaction–based DNA genotyping for diagnosis.

Data Sources.—

Sources are the author's 10-year experience using ancillary techniques for the evaluation of potentially molar specimens in a large gynecologic pathology practice and the literature.

Conclusions.—

The unique genetics of complete hydatidiform moles (purely androgenetic), partial hydatidiform moles (diandric triploid), and nonmolar specimens (biparental, with allelic balance) allow for certain techniques, including immunohistochemical analysis of p57 expression (a paternally imprinted, maternally expressed gene) and genotyping, to refine diagnoses of hydatidiform moles. Although p57 immunostaining alone can identify complete hydatidiform moles, which lack p57 expression because of a lack of maternal DNA, this analysis does not distinguish partial hydatidiform moles from nonmolar specimens because both express p57 because of the presence of maternal DNA. Genotyping, which compares villous and decidual DNA patterns to determine the parental source and ratios of polymorphic alleles, distinguishes purely androgenetic complete hydatidiform moles from diandric triploid partial hydatidiform moles, and both of these from biparental nonmolar specimens. An algorithmic approach to diagnosis using these techniques is advocated.

Hydatidiform moles are abnormal placentas with distinct genetic characteristics/alterations that are responsible for inducing variable trophoblastic proliferation and hydropic change in villous tissue. A comprehensive discussion of the epidemiology and pathogenetic mechanisms of molar pregnancies, which is beyond the scope of the current article, has been provided in a recent review.1  Distinction of hydatidiform moles from nonmolar specimens and subclassification of hydatidiform moles as complete hydatidiform mole (CHM) versus partial hydatidiform mole (PHM) are important for both clinical practice and investigational studies. The risk of persistent gestational trophoblastic disease (GTD) and clinical management differ for CHMs, PHMs, and nonmolar specimens. However, diagnosis based solely on morphology is subject to diagnostic variability. The unique genetic features of CHMs (purely androgenetic conceptions), PHMs (diandric triploid conceptions), and nonmolar specimens (biparental conceptions with allelic balance) allow for certain molecular techniques, including immunohistochemical analysis of p57 expression (a paternally imprinted, maternally expressed gene) and DNA genotyping, to refine the diagnosis of hydatidiform moles. Although p57 immunostaining alone can identify CHMs, which lack p57 expression because of the lack of maternal DNA, this analysis cannot distinguish PHMs from nonmolar specimens because both express p57 because of the presence of maternal DNA. Polymerase chain reaction (PCR)–based DNA genotyping, which can determine the parental source and ratios of polymorphic alleles, specifically distinguishes purely androgenetic CHMs from diandric triploid PHMs, and both of these from biparental nonmolar specimens. The objectives of this review are:

  1. To present the classification and differential diagnosis of hydatidiform moles;

  2. To discuss the genetics of molar and nonmolar specimens and explain how ancillary techniques target these unique genetic features to establish diagnostic truth;

  3. To highlight the issue of diagnostic reproducibility for hydatidiform moles and discuss the importance of accurate diagnosis;

  4. To illustrate the utility of p57 immunohistochemistry for diagnosis of hydatidiform moles and provide guidance on interpretation;

  5. To demonstrate the application of DNA genotyping for diagnosis of hydatidiform moles;

  6. To provide an algorithmic approach for diagnosis of hydatidiform moles in the molecular era.

CLASSIFICATION AND DIFFERENTIAL DIAGNOSIS OF HYDATIDIFORM MOLES

Table 1 lists the classification and differential diagnosis of hydatidiform moles. Hydatidiform moles include 2 varieties: the complete hydatidiform mole (CHM) and the partial hydatidiform mole (PHM). In addition, an early form of CHM has been recognized. Typical CHMs are comprised of enlarged edematous villi with moderate to marked circumferential trophoblastic hyperplasia, often with cytologic atypia, prominent central cistern formation, and trophoblastic inclusions.24  Early CHMs are characterized by a redundant bulbous villous growth pattern, hypercellular myxoid villous stroma, a labyrinthine network of villous stromal canalicular vascular structures, karyorrhectic debris within stroma, and at least focal trophoblastic hyperplasia on villi and the undersurface of the chorionic plate.5  Characteristic morphologic features of PHMs include the presence of 2 populations of villi (large, irregular, hydropic villi, and small, immature, fibrotic villi), cisterns in some enlarged villi, markedly irregular villi with scalloped borders and trophoblastic inclusions, and generally mild circumferential trophoblastic hyperplasia.2,3,69  Invasive hydatidiform moles, which invade the myometrium, are virtually always CHMs.10  Examples are provided in Figure 1, A through F.

Table 1

Classification and Differential Diagnosis of Hydatidiform Moles

Classification and Differential Diagnosis of Hydatidiform Moles
Classification and Differential Diagnosis of Hydatidiform Moles
Figure 1

A and B, Complete hydatidiform mole. Hydropically enlarged villi have trophoblastic hyperplasia (A) as well as cisterns and trophoblastic inclusions (B). C and D, Early complete hydatidiform mole. Cauliflower-like villi have trophoblastic hyperplasia, and cellular myxoid stroma contains canalicular vascular structures and karyorrhectic nuclear debris. E and F, Partial hydatidiform mole. Irregularly shaped villi have scalloped contours, mild trophoblastic hyperplasia, and trophoblastic inclusions. G and H, Nonmolar abnormal villous morphology associated with trisomy. Variably sized, irregularly shaped villi with focal mild trophoblastic hyperplasia simulate a partial hydatidiform mole. I and J, Early nonmolar abortus. Immature chorionic villi have polarized trophoblastic hyperplasia. K and L, Hydropic abortus. Villi are edematous but lack other features of a hydatidiform mole. M and N, Nonmolar androgenetic/biparental mosaic conception. Hydropically enlarged villi have cisterns, trophoblastic inclusions, and areas of cellular villous stroma with notable vessels but completely lack trophoblastic hyperplasia. O and P, Early complete hydatidiform mole arising in an androgenetic/biparental mosaic conception. Cauliflower-like villi with trophoblastic hyperplasia and myxoid stroma (O, upper; P) are an early complete hydatidiform mole component (p57 [not shown]). Smaller edematous villi lacking trophoblastic hyperplasia (O, lower) are an androgenetic/biparental mosaic component (p57+ cytotrophoblast and p57 stromal cells [not shown; see Figure 8, D, for another example]).

Figure 1

A and B, Complete hydatidiform mole. Hydropically enlarged villi have trophoblastic hyperplasia (A) as well as cisterns and trophoblastic inclusions (B). C and D, Early complete hydatidiform mole. Cauliflower-like villi have trophoblastic hyperplasia, and cellular myxoid stroma contains canalicular vascular structures and karyorrhectic nuclear debris. E and F, Partial hydatidiform mole. Irregularly shaped villi have scalloped contours, mild trophoblastic hyperplasia, and trophoblastic inclusions. G and H, Nonmolar abnormal villous morphology associated with trisomy. Variably sized, irregularly shaped villi with focal mild trophoblastic hyperplasia simulate a partial hydatidiform mole. I and J, Early nonmolar abortus. Immature chorionic villi have polarized trophoblastic hyperplasia. K and L, Hydropic abortus. Villi are edematous but lack other features of a hydatidiform mole. M and N, Nonmolar androgenetic/biparental mosaic conception. Hydropically enlarged villi have cisterns, trophoblastic inclusions, and areas of cellular villous stroma with notable vessels but completely lack trophoblastic hyperplasia. O and P, Early complete hydatidiform mole arising in an androgenetic/biparental mosaic conception. Cauliflower-like villi with trophoblastic hyperplasia and myxoid stroma (O, upper; P) are an early complete hydatidiform mole component (p57 [not shown]). Smaller edematous villi lacking trophoblastic hyperplasia (O, lower) are an androgenetic/biparental mosaic component (p57+ cytotrophoblast and p57 stromal cells [not shown; see Figure 8, D, for another example]).

The differential diagnosis of hydatidiform moles includes a variety of nonmolar entities that can exhibit some features suggestive of a molar pregnancy. These include products of conception specimens with abnormal villous morphology, early nonmolar specimens with prominent trophoblastic hyperplasia, hydropic abortuses, and androgenetic/biparental mosaic conceptions. Abnormal villous morphology is a term used to label cases in which villi have some dysmorphic features suggestive of a hydatidiform mole, usually a PHM but sometimes an early CHM, but lack fully developed diagnostic features of either type. In some cases these changes are associated with other (nonmolar) genetic abnormalities, such as trisomy.1115  Early nonmolar specimens at times have trophoblastic proliferation that is sufficiently prominent to raise concern for a CHM, usually an early CHM, but lack other features of a hydatidiform mole. In the earliest examples, the trophoblastic proliferation forms a circumferential shell around a very early conceptus, but once some branching of immature villi occurs, the trophoblastic proliferation usually can be recognized as polarized when a radiating pattern from the tips of the villi is appreciated. Hydropic abortuses have edematous villi but lack other features of a hydatidiform mole; any trophoblastic proliferation is generally polarized at one end of the villous structures. Nonmolar androgenetic/biparental mosaic conceptions are unusual specimens which, when encountered at an early gestational age, represent the early form of placental mesenchymal dysplasia. They are characterized by hydropic villi, which can have some cisterns and trophoblastic inclusions, often with some villi having more cellular stroma and notable vascular proliferation, but the villi lack trophoblastic hyperplasia. Some androgenetic/biparental mosaic conceptions also have a molar component in which the villi have trophoblastic hyperplasia and the other features of a CHM; the molar component can be focal and inconspicuous with features of the early form, or it can be more fully developed and readily apparent. Examples of these entities are provided in Figure 1, G through P. In addition, because the individual subtypes of hydatidiform moles can exhibit a spectrum of morphologic features, depending in part on gestational age, CHMs (including the early form) and PHMs are often in the differential diagnosis of one another as well. Parameters assessed to distinguish the subtypes of hydatidiform moles, including variations in the sizes and shapes of the villi, the extent of hydropic change, and the degree of trophoblastic hyperplasia, have sufficiently wide spectra to result in some morphologic overlap between a subset of CHMs and PHMs, namely, those at the lower and upper ends, respectively, of their morphologic spectra.

GENETICS OF HYDATIDIFORM MOLES AND NONMOLAR SPECIMENS

The distinct genetics of molar specimens are illustrated in Figure 2. CHMs are purely androgenetic conceptions (only paternal genetic material is present) and usually diploid (2 paternal chromosome complements without a maternal chromosome complement)16 ; most result from fertilization of an ovum devoid of maternal genetic material by a single sperm that duplicates (monospermy; ∼85%),1719  but a subset is due to fertilization by 2 sperm (dispermy).20  Some CHMs are tetraploid rather than diploid, but these are also purely androgenetic. A rare form of CHM, the familial biparental CHM, is not androgenetic but rather is related to mutations in maternal effect genes NLRP7 (NALP7; chromosome 19) and KHDC3L (C6orf221; chromosome 6), which result in global imprinting alteration leading to preferential expression of paternally imprinted genes in villous trophoblast.2123  In contrast, PHMs are characterized by diandric triploidy (2 paternal and 1 maternal chromosome complements), with most arising by fertilization of an ovum by 2 sperm (dispermy; ∼99%).19,2426  Rare examples of PHMs exhibit triandric tetraploidy (3 paternal and 1 maternal chromosome complements).27  Nonmolar specimens are usually characterized by biparental diploidy (1 paternal and 1 maternal chromosome complements), but some can be tetraploid. Some nonmolar specimens are digynic triploid conceptions (2 maternal and 1 paternal chromosome complements). In most cases, digynic triploid conceptions do not exhibit molar features,26,28  but on occasion they can have some focal dysmorphic features suggesting a PHM,29  and rare examples occurring in patients with familial recurrent hydatidiform mole associated with mutations in NLRP7 (NALP7) or KHDC3L (C6orf221) can have the morphology and immunophenotype (p57) of a CHM.30  Nonmolar specimens with cytogenetic abnormalities, such as trisomy, can have dysmorphic villi suggesting or simulating PHMs.11,12,29  Androgenetic/biparental mosaic conceptions are genetically distinct from typical hydatidiform moles. The nonmolar forms comprise villi with varying admixtures of both androgenetic (p57) and biparental (p57+) cell lines within individual villi (often segregated as biparental cytotrophoblast and androgenetic stromal cells, but the reverse is possible); these cell lines are most often both diploid but can be a mixture of diploid and triploid or even tetraploid cells.14,3134  Androgenetic/biparental mosaic conceptions with a molar component, which is most often a CHM/early CHM, have in addition a population of purely androgenetic villi (see the section on ancillary techniques for more details).

Figure 2

Genetics of hydatidiform moles. A, Complete hydatidiform mole. Most commonly, 1 sperm enters an ovum devoid of maternal nuclear genetic material and duplicates, giving rise to a purely androgenetic conception (paternal genome only), which is usually diploid (∼85% monospermic/homozygous). B, Partial hydatidiform mole. Most commonly, 2 sperm fertilize an ovum, giving rise to a diandric monogynic triploid conception (∼99% dispermic/heterozygous).

Figure 2

Genetics of hydatidiform moles. A, Complete hydatidiform mole. Most commonly, 1 sperm enters an ovum devoid of maternal nuclear genetic material and duplicates, giving rise to a purely androgenetic conception (paternal genome only), which is usually diploid (∼85% monospermic/homozygous). B, Partial hydatidiform mole. Most commonly, 2 sperm fertilize an ovum, giving rise to a diandric monogynic triploid conception (∼99% dispermic/heterozygous).

DIAGNOSTIC REPRODUCIBILITY AND IMPORTANCE OF ACCURATE CLASSIFICATION OF MOLAR AND NONMOLAR SPECIMENS

The diagnosis of hydatidiform moles can often be accomplished on the basis of morphologic assessment alone when characteristic features are well developed. However, a number of studies have demonstrated that there is diagnostic variability (suboptimal interobserver and intraobserver reproducibility) for hydatidiform moles based on routine assessment of hematoxylin-eosin–stained slides, even among experienced pathologists with specialized training.3541  In general, problems in classification can be attributed to several factors, including imperfect histologic criteria for diagnosing hydatidiform moles, variability in how pathologists apply diagnostic criteria, and the known variation in morphologic features dependent on the gestational age of the specimen. With the widespread use of routine first-trimester ultrasonography, the latter factor has become significant because most products of conception specimens, including molar and nonmolar ones, are encountered at much earlier gestational ages when histologic features are less well developed.42  Examples from a reproducibility study in which diagnoses were established using ancillary techniques are shown in Figures 3 and 4, with details for the cases in these figures provided in Table 2; summary data from the study are provided in Supplemental Figure 1 (find supplemental digital content at www.archivesofpathology.org in the December 2018 table of contents; see the section on ancillary techniques for details of those diagnostic methods).40,41 

Figure 3

Examples of hydatidiform moles with well-developed morphologic features from a reproducibility study. A through C, Complete hydatidiform mole, p57, genotyping-proven androgenetic. This example was uniformly recognized as a complete hydatidiform mole by morphology, and p57 was uniformly interpreted as negative. D through F, Partial hydatidiform mole, p57+, genotyping-proven diandric triploid. This example was uniformly recognized as a partial hydatidiform mole by morphology, and p57 was uniformly interpreted as positive (see Table 2 for details).

Figure 3

Examples of hydatidiform moles with well-developed morphologic features from a reproducibility study. A through C, Complete hydatidiform mole, p57, genotyping-proven androgenetic. This example was uniformly recognized as a complete hydatidiform mole by morphology, and p57 was uniformly interpreted as negative. D through F, Partial hydatidiform mole, p57+, genotyping-proven diandric triploid. This example was uniformly recognized as a partial hydatidiform mole by morphology, and p57 was uniformly interpreted as positive (see Table 2 for details).

Figure 4

Challenging examples of hydatidiform moles from a reproducibility study. A through C, Complete hydatidiform mole, p57, genotyping-proven androgenetic. This example was recognized as molar, but the consensus diagnosis by morphologic assessment was a partial hydatidiform mole. When p57 was used, the consensus interpretation was a complete hydatidiform mole. D through F, Complete hydatidiform mole, p57, genotyping-proven androgenetic. There was no consensus diagnosis in either of 2 rounds assessing morphology. When p57 was used, the consensus interpretation was a complete hydatidiform mole (see Table 2 for details).

Figure 4

Challenging examples of hydatidiform moles from a reproducibility study. A through C, Complete hydatidiform mole, p57, genotyping-proven androgenetic. This example was recognized as molar, but the consensus diagnosis by morphologic assessment was a partial hydatidiform mole. When p57 was used, the consensus interpretation was a complete hydatidiform mole. D through F, Complete hydatidiform mole, p57, genotyping-proven androgenetic. There was no consensus diagnosis in either of 2 rounds assessing morphology. When p57 was used, the consensus interpretation was a complete hydatidiform mole (see Table 2 for details).

Table 2

Diagnostic Reproducibility Data for Examples in Figures 3 and 4 

Diagnostic Reproducibility Data for Examples in Figures 3 and 4
Diagnostic Reproducibility Data for Examples in Figures 3 and 4

Distinction of hydatidiform moles from nonmolar specimens and the subclassification of hydatidiform moles as CHM versus PHM are important for both clinical practice and investigational studies. Accurate classification is critical to ascertaining the actual risk of persistent gestational trophoblastic disease (GTD) associated with the various subtypes of hydatidiform moles and determining the appropriate nature and duration of clinical follow-up. Both underdiagnosis and overdiagnosis of hydatidiform moles can result in a faulty estimation of the risk of persistent GTD and improper clinical management. The risk of persistent GTD and clinical management differ for CHMs, PHMs, and nonmolar specimens.3,4346  Based on well-defined cases in the modern literature, the risk of persistent GTD following CHM is 9% to 20%, whereas persistent GTD following a PHM is 0% to 4%.4651  Most cases of persistent GTD following a hydatidiform mole are invasive moles, but 3% to 5% present as choriocarcinoma. Despite the lower risk associated with PHMs, metastatic GTD and trophoblastic tumors (choriocarcinoma and placental site trophoblastic tumor) coexistent with or subsequent to a diagnosis of a well-documented PHM have been reported.5256  Hence, although localized and metastatic persistent GTD is much more common after a diagnosis of CHM, it can and does occur following a PHM. Consequently, patients with PHMs should receive follow-up with serum β-human chorionic gonadotropin (hCG) levels in conjunction with contraception until undetectable levels are obtained. The risk of persistent GTD for familial biparental CHMs is similar to that of sporadic androgenetic CHMs. In contrast, because persistent GTD following a first-trimester nonmolar spontaneous abortion is rare (estimated risk of ≤0.0002%),57  spontaneous abortion or termination of a nonmolar pregnancy does not inherently warrant follow-up with serum hCG levels or contraception until undetectable levels are obtained. Thus, avoiding misclassification of nonmolar specimens, particularly those with abnormal villous morphology, as PHMs is of particular importance to patients with infertility for whom mandated contraception during a period of hCG monitoring (even if abbreviated) is undesirable.

ANCILLARY TECHNIQUES FOR REFINED DIAGNOSIS OF MOLAR AND NONMOLAR SPECIMENS

In view of the limitations of morphologic assessment and the clinical importance of accurate diagnosis of molar specimens, use of ancillary techniques to refine the diagnosis of hydatidiform moles is recommended.1  The value of immunohistochemical analysis of p57 expression19,31,32,5868  and DNA genotyping via PCR amplification of short tandem repeat (STR) loci14,19,29,64,66,6974  for improving the diagnosis of hydatidiform moles has been demonstrated in a number of studies. These techniques exploit the unique genetic features of molar and nonmolar specimens to improve diagnostic accuracy.

Immunohistochemical Analysis of p57 Expression

p57 is the gene product of the paternally imprinted, maternally expressed gene CDKN1C, a cyclin-dependent kinase inhibitor located on chromosome 11p15.5. CHMs, including the early forms, which lack a maternal genetic contribution, have absent (or very limited) p57 expression in villous cytotrophoblast and villous stromal cells (Figure 5, A). In contrast, both PHMs and nonmolar specimens (including those with abnormal villous morphology) contain a maternal chromosome complement and exhibit diffuse p57 expression in these cell types (Figure 5, B and C). This differential p57 expression has been found to be useful in the distinction of CHMs (including early forms) from PHMs and nonmolar specimens.19,31,32,5868  In addition, interpretation of p57 immunostains is highly reproducible.40,41  However, this marker has the limitation of not being able to discern PHMs from nonmolar specimens (the latter including both biparental diploid nonmolar specimens and digynic triploid nonmolar specimens) because all of these entities maintain p57 expression due to the presence of a maternal chromosome complement. Therefore, other methods, such as genotyping, are required to definitively distinguish PHMs from nonmolar specimens.

Figure 5

Mechanism of p57 expression in molar and nonmolar specimens. A, An androgenetic complete hydatidiform mole has aberrant loss of p57 expression because the maternal copy is absent (no expression from methylated paternal copies). Immunohistochemical analysis of p57 expression demonstrates that the nuclei of villous cytotrophoblast and stromal cells are negative (intermediate trophoblastic cells are always positive and serve as internal positive control). B, A partial hydatidiform mole has normal expression of p57 from the maternal copy. Immunohistochemical analysis of p57 expression demonstrates that the nuclei of villous cytotrophoblast and stromal cells are positive (intermediate trophoblastic cells are also positive). C, A biparental nonmolar conception has normal expression of p57 from the maternal copy. Immunohistochemical analysis of p57 expression demonstrates that the nuclei of villous cytotrophoblast and stromal cells are positive (aggregates of intermediate trophoblastic cells are also positive).

Figure 5

Mechanism of p57 expression in molar and nonmolar specimens. A, An androgenetic complete hydatidiform mole has aberrant loss of p57 expression because the maternal copy is absent (no expression from methylated paternal copies). Immunohistochemical analysis of p57 expression demonstrates that the nuclei of villous cytotrophoblast and stromal cells are negative (intermediate trophoblastic cells are always positive and serve as internal positive control). B, A partial hydatidiform mole has normal expression of p57 from the maternal copy. Immunohistochemical analysis of p57 expression demonstrates that the nuclei of villous cytotrophoblast and stromal cells are positive (intermediate trophoblastic cells are also positive). C, A biparental nonmolar conception has normal expression of p57 from the maternal copy. Immunohistochemical analysis of p57 expression demonstrates that the nuclei of villous cytotrophoblast and stromal cells are positive (aggregates of intermediate trophoblastic cells are also positive).

To interpret immunohistochemical stains for p57, the presence or absence of nuclear positivity is assessed in villous cytotrophoblast and villous stromal cells, as well as in any intermediate trophoblastic cells and maternal decidua present in the stained section. The p57 immunostain is interpreted as “negative” when villous cytotrophoblast and villous stromal cells are either entirely negative or demonstrate only limited expression (nuclear staining in <10% of these cell types). It is important to also assess the adequacy of the stain by identifying the presence of nuclear p57 expression in intermediate trophoblastic cells and/or maternal decidual cells. Expression in these cellular components serves as an internal positive control in all cases, including CHMs. Expression of p57 in the intermediate trophoblast of CHMs is thought to be related to “epigenetic relaxation” (expression from the paternal copy of the gene because a maternal copy is lacking). The p57 immunostain is interpreted as “positive” when the extent of staining is extensive or diffuse in these cell types (expression in >50% of these cells). The interpretation of p57 immunohistochemistry is typically straightforward in that the cellular components in which p57 is differentially expressed (villous cytotrophoblast and villous stromal cells) are almost always uniformly negative or diffusely positive; intermediate/focally positive, discordant, or divergent staining patterns in these cell types are uncommonly encountered. A few studies have described a limited extent of p57 expression (scattered nuclear positivity in villous cytotrophoblast and villous stromal cells) in a minority of cases of both diploid and tetraploid CHMs; this limited extent of expression (present in <10% of these cell types) is still considered compatible with a diagnosis of CHM.58,61,62  Typical examples of p57 staining patterns in a CHM, a PHM, and a nonmolar specimen are illustrated in Figure 6. It is also important to ensure that p57 expression in intermediate trophoblastic cells and decidua is at the appropriate level and demonstrates only nuclear expression without excessive nonspecific cytoplasmic staining. When the latter occurs, it is possible to generate some degree of p57 expression in the villous cytotrophoblast and/or stromal cells of a CHM, leading to erroneous interpretation as a positive result that would exclude a diagnosis of a CHM (Figure 7).

Figure 6

Examples of p57 expression in typical molar and nonmolar specimens. A and B, Early complete hydatidiform mole, with negative p57 immunostain. Villous cytotrophoblast and stromal cells are negative; intermediate trophoblastic cells are positive, serving as an internal positive control. Genotyping confirmed this as a purely androgenetic conception (see Figure 11, B). C and D, Partial hydatidiform mole, with positive p57 immunostain. Villous cytotrophoblast and stromal cells are positive. Genotyping confirmed this as a diandric triploid conception (see Figure 11, D). E and F, Nonmolar abnormal villous morphology related to trisomy, with positive p57 immunostain. Villous cytotrophoblast and stromal cells are positive. The features simulate a partial hydatidiform mole, and the p57 result does not distinguish these entities. Genotyping confirmed this as a biparental conception with allelic balance and a trisomy (see Figure 12, B).

Figure 6

Examples of p57 expression in typical molar and nonmolar specimens. A and B, Early complete hydatidiform mole, with negative p57 immunostain. Villous cytotrophoblast and stromal cells are negative; intermediate trophoblastic cells are positive, serving as an internal positive control. Genotyping confirmed this as a purely androgenetic conception (see Figure 11, B). C and D, Partial hydatidiform mole, with positive p57 immunostain. Villous cytotrophoblast and stromal cells are positive. Genotyping confirmed this as a diandric triploid conception (see Figure 11, D). E and F, Nonmolar abnormal villous morphology related to trisomy, with positive p57 immunostain. Villous cytotrophoblast and stromal cells are positive. The features simulate a partial hydatidiform mole, and the p57 result does not distinguish these entities. Genotyping confirmed this as a biparental conception with allelic balance and a trisomy (see Figure 12, B).

Figure 7

Complete hydatidiform mole with different p57 results obtained in different laboratories related to technical factors. A and B. Villi show typical features of a complete hydatidiform mole. C, The p57 immunostain performed in the originating laboratory demonstrates positivity in villous cytotrophoblast and stromal cells, which led to doubt regarding the morphologic diagnostic impression and a request for consultation. D, Decidual tissue on the p57 immunostain has higher than desirable nonspecific cytoplasmic staining, indicating that the positive result may be unreliable. E, The p57 immunostain performed in the consulting laboratory is negative (with adequate internal positive control in intermediate trophoblastic cells), confirming the morphologic impression. F, Decidual tissue on the p57 immunostain from the consulting laboratory demonstrates the appropriate nuclear expression without any nonspecific cytoplasmic staining. Genotyping confirmed this as a purely androgenetic conception.

Figure 7

Complete hydatidiform mole with different p57 results obtained in different laboratories related to technical factors. A and B. Villi show typical features of a complete hydatidiform mole. C, The p57 immunostain performed in the originating laboratory demonstrates positivity in villous cytotrophoblast and stromal cells, which led to doubt regarding the morphologic diagnostic impression and a request for consultation. D, Decidual tissue on the p57 immunostain has higher than desirable nonspecific cytoplasmic staining, indicating that the positive result may be unreliable. E, The p57 immunostain performed in the consulting laboratory is negative (with adequate internal positive control in intermediate trophoblastic cells), confirming the morphologic impression. F, Decidual tissue on the p57 immunostain from the consulting laboratory demonstrates the appropriate nuclear expression without any nonspecific cytoplasmic staining. Genotyping confirmed this as a purely androgenetic conception.

In addition to the typical diffusely positive p57 staining result, variants of positive staining can be encountered occasionally. A p57 immunostain can be considered as “focally positive” when nuclear expression in both villous stromal cells and cytotrophoblast is in the focally positive range (>10% but <50% of the villi in the stained section). In our experience, this degree of staining has only been encountered in PHMs (with some frequency) and nonmolar specimens, but never in molecularly confirmed CHMs, so interpretation as a fundamentally positive result is justified. The p57 immunostain is interpreted as “discordant” when there is any combination/admixture of negative and positive results for villous cytotrophoblast and villous stromal cells within individual villi, including positive staining in cytotrophoblast and negative staining in villous stromal cells (most cases), or vice versa. Discordant p57 expression is characteristic of androgenetic/biparental mosaic conceptions, with discordant expression in different cell types based on the presence or absence of maternal genetic material in those particular cells. In these cases, the p57 cells are androgenetic (usually diploid) and the p57+ cells are biparental (usually also diploid, but some can be triploid or tetraploid or a mixture of these).31,32,34  The p57 immunostain is interpreted as “divergent” when 2 populations of villi, each with different morphologies, exhibit 2 different staining patterns (eg, a typical “negative” result in one set and typical “positive” result in the other set). A twin gestation comprising a typical androgenetic diploid CHM with a lack of p57 expression and a typical biparental diploid nonmolar abortus with a positive p57 result exemplifies this situation.14  Another form of divergent p57 expression (also with discordant expression) is encountered in androgenetic/biparental mosaic conceptions with a molar component (Figure 8). In these cases, the nonmolar androgenetic/biparental mosaic component has discordant p57 expression—usually positive staining in cytotrophoblastic cells and negative staining in villous stromal cells (Figure 8, B through D)—and the molar component, which has features of a CHM, is negative for p57 (Figure 8, E through H); thus, the 2 components have divergent patterns relative to each other (1 discordant and 1 negative).

Figure 8

Androgenetic/biparental mosaic conception with a molar component. A, A mixture of hydropically enlarged villi with trophoblastic hyperplasia and smaller hydropic villi lacking trophoblastic hyperplasia can be misinterpreted as a partial hydatidiform mole on the basis of 2 populations of villi with focal trophoblastic hyperplasia. B through D, Villous component lacking trophoblastic hyperplasia has a discordant pattern of p57 expression, with positive staining in villous cytotrophoblastic cells and negative stromal cells, indicating a mixture of androgenetic (p57) and biparental (p57+) cells. Genotyping confirmed this component as mosaic with aberrant allele ratios enriched for paternal alleles (see Figure 12, D). E through H, Villous component with trophoblastic hyperplasia is negative for p57, indicating a molar component consistent with complete hydatidiform mole. Genotyping confirmed this component as purely androgenetic (see Figure 12, D). Some villi can have a hybrid of molar and mosaic features (G).

Figure 8

Androgenetic/biparental mosaic conception with a molar component. A, A mixture of hydropically enlarged villi with trophoblastic hyperplasia and smaller hydropic villi lacking trophoblastic hyperplasia can be misinterpreted as a partial hydatidiform mole on the basis of 2 populations of villi with focal trophoblastic hyperplasia. B through D, Villous component lacking trophoblastic hyperplasia has a discordant pattern of p57 expression, with positive staining in villous cytotrophoblastic cells and negative stromal cells, indicating a mixture of androgenetic (p57) and biparental (p57+) cells. Genotyping confirmed this component as mosaic with aberrant allele ratios enriched for paternal alleles (see Figure 12, D). E through H, Villous component with trophoblastic hyperplasia is negative for p57, indicating a molar component consistent with complete hydatidiform mole. Genotyping confirmed this component as purely androgenetic (see Figure 12, D). Some villi can have a hybrid of molar and mosaic features (G).

In addition to these variants of positive p57 results, both aberrant retention and loss of p57 expression are rarely encountered in specific situations. Two molecularly confirmed androgenetic CHMs with diffuse p57 expression attributable to a retained maternal chromosome 11 (location of the p57 gene) have been described (Figure 9, A and B).75,76  Two molecularly confirmed PHMs—one diandric triploid and the other triandric tetraploid—with loss of p57 expression attributable to loss of the maternal copy of chromosome 11 have been reported (Figure 9, C and D).19,77 

Figure 9

Examples of aberrant p57 expression. A and B, Complete hydatidiform mole with aberrant p57 expression attributable to a retained maternal copy of chromosome 11 (location of p57). Villi demonstrate typical features of a complete hydatidiform mole, but diffuse p57 expression in villous cytotrophoblast and stromal cells is not expected for that diagnosis. Genotyping demonstrated a purely androgenetic conception with the exception of the locus on chromosome 11, where there was evidence of trisomy (2 paternal copies and 1 maternal copy). C and D, Partial hydatidiform mole with aberrant loss of p57 expression attributable to loss of the maternal copy of chromosome 11. Villi demonstrate features suggesting an early complete hydatidiform mole, and the loss of p57 expression would support that interpretation. However, genotyping demonstrated a diandric triploid conception with the exception of the locus on chromosome 11, where there was evidence of uniparental disomy (2 paternal copies and no maternal copies).

Figure 9

Examples of aberrant p57 expression. A and B, Complete hydatidiform mole with aberrant p57 expression attributable to a retained maternal copy of chromosome 11 (location of p57). Villi demonstrate typical features of a complete hydatidiform mole, but diffuse p57 expression in villous cytotrophoblast and stromal cells is not expected for that diagnosis. Genotyping demonstrated a purely androgenetic conception with the exception of the locus on chromosome 11, where there was evidence of trisomy (2 paternal copies and 1 maternal copy). C and D, Partial hydatidiform mole with aberrant loss of p57 expression attributable to loss of the maternal copy of chromosome 11. Villi demonstrate features suggesting an early complete hydatidiform mole, and the loss of p57 expression would support that interpretation. However, genotyping demonstrated a diandric triploid conception with the exception of the locus on chromosome 11, where there was evidence of uniparental disomy (2 paternal copies and no maternal copies).

DNA Genotyping

Molecular genetic analysis of the type provided by PCR-based DNA (STR) genotyping offers greater diagnostic discriminatory capability than other genetic techniques in that CHMs, PHMs, and nonmolar specimens can be distinguished from one another by specifically discerning the purely androgenetic nature of CHMs from the diandric triploidy of PHMs, and both of these from the biparental allelic balance of nonmolar specimens.19,64,66,69,70,73,74  Thus, this technique can establish diagnostic truth. Other ancillary techniques, including conventional cytogenetics (karyotype), DNA ploidy analysis (flow cytometry, image analysis), and fluorescence in situ hybridization, have the limitation of not being able to establish maternal/parental contributions of chromosome complements and cannot absolutely determine the true diagnosis. Thus, although diploid and triploid results obtained with these latter techniques can improve recognition of CHMs and PHMs in the context of sufficiently developed morphologic alterations, CHMs (particularly some early forms) cannot be distinguished from nonmolar specimens (both yield nonspecific diploid results), and PHMs cannot be distinguished from digynic triploid nonmolar specimens (both yield nonspecific triploid results) on the basis of these results alone and when morphologic abnormalities are subtle or overlapping (Table 3). DNA genotyping is particularly important for the diagnosis of PHMs, which continue to pose diagnostic difficulty and cannot be distinguished from nonmolar specimens because of shared p57 expression patterns. This technique, used in conjunction with morphology, is the best one suited for ensuring that specimens interpreted as PHMs are in fact diandric triploid gestations, thus preventing misclassification of early CHMs, nonmolar specimens with abnormal villous morphology, and even digynic triploid specimens as PHMs. Digynic triploid specimens usually do not exhibit the morphologic features of PHMs,26,28  but on occasion the villi can have some focal dysmorphic features to suggest a PHM,29  which can lead to potential overdiagnosis as such if ploidy analysis, rather than DNA genotyping, is used.

Table 3

Methods for Distinction of Molar and Nonmolar Specimens

Methods for Distinction of Molar and Nonmolar Specimens
Methods for Distinction of Molar and Nonmolar Specimens

STRs are repetitive DNA sequences that are highly polymorphic in the population. These genetic markers have been developed for identity, forensic, criminal, and relationship (paternity) testing. DNA genotyping using STR analysis generally involves PCR amplification of multiple STR loci using fluorescently labeled PCR primers, followed by sizing of the PCR products by capillary electrophoresis (Figure 10, A). The material used for analysis is formalin-fixed, paraffin-embedded tissue sections. Areas of pure villous and decidual tissue are identified on a stained section, which is used to guide macrodissection of these tissues from serial unstained sections (Figure 10, B through D). For the analysis of hydatidiform moles, the alleles at each locus are identified for both the maternal (decidua) and villous tissues, and the patterns are compared. Alleles in the villous tissue are identified as paternal (nonmaternal) or likely maternal (also possibly paternal because of shared alleles). The copy number/dosage of each allele relative to the other can be determined by calculating an allelic ratio, which compares either the peak height or peak area of the 2 alleles. In general, when 2 alleles are present in equal dosage, the ratio will be approximately 1:1. When 1 allele is in double dosage compared with the other (eg, trisomy/triploidy), the ratio will be approximately 2:1. Specific details for the interpretation of STR data can be found elsewhere.71  Diagrams illustrating the cellular components of molar, nonmolar, and mosaic entities and corresponding genotyping data are provided in Figures 11 and 12. Complete hydatidiform moles are composed of p57 androgenetic villous cytotrophoblastic cells and p57 androgenetic stromal cells, and are usually diploid. By genotyping, they are diagnosed by the finding of purely androgenetic alleles at informative loci; this most commonly manifests as a single nonmaternal allele at each informative locus because of the monospermic origin (Figure 11, A and B). Although the vast majority are characterized by androgenetic diploidy, a small subset can have androgenetic tetraploidy (genotyping does not specifically distinguish diploid examples from tetraploid examples because peak heights do not indicate actual DNA content). The PHMs are composed of p57+ diandric triploid villous cytotrophoblastic cells and stromal cells. By genotyping, they are diagnosed by the finding of paternal to maternal allele ratios of 2:1 at informative loci. This is manifested as either 3 unique alleles, 2 paternal and 1 maternal, with equal ratios, or as 2 alleles with a 2:1 ratio and with the allele in double dosage being paternal (Figure 11, C and D). Rare triandric tetraploid examples (4 sets of chromosome complements, with 1 maternal in origin and 3 paternal in origin) have paternal to maternal allele ratios of 3:1 at informative loci. Nonmolar specimens are most often composed of p57+ biparental diploid cells. They are diagnosed as such when the genotyping demonstrates balanced biparental allele ratios (ratios of 1:1) at informative loci (Figure 12, A and B). Those with abnormal villous morphology related to other nonmolar genetic alterations, such as trisomy, can have an altered ratio at one or even a few loci if the affected chromosomes are covered by the markers used in the genotyping kit. The number of loci with imbalanced ratios and the allele pattern will depend on the number of chromosomes involved and the parental source, but most loci will have balanced biparental allele ratios. Nonmolar specimens with digynic triploidy will have 2:1 allele ratios at informative loci, but none of these will demonstrate evidence of 2 novel/obligate paternal alleles. Nonmolar mosaic conceptions most commonly are composed of villi with a mixture of p57+ biparental villous cytotrophoblastic cells and p57 androgenetic villous stromal cells (p57-discordant villi). By genotyping, they demonstrate an excess of androgenetic alleles with variable paternal to maternal allele ratios typically greater than 2:1 at informative loci, reflecting the admixture of androgenetic and biparental cell lines within individual villi (enrichment for paternal alleles attributable to the mixture of some cells with 2 paternal copies [no maternal copy] and other cells with 1 paternal and 1 maternal copy of a given allele; Figure 12, C and D). Androgenetic/biparental mosaic conceptions with a nonmolar mosaic component and a molar component showing features of a CHM comprise p57-discordant and p57 villi, respectively, with each component being similar to the pure forms of these entities. When each component can be individually genotyped, the results generated will also be the same as for the pure forms of these entities (Figure 12, C and D).

Figure 10

Methods for genotyping. A, Polymerase chain reaction amplification of short tandem repeat loci. Fluorescently labeled primers are used to amplify each locus to generate copies of the maternal and paternal alleles. When these are of different sizes (heterozygous, locus 1), this will generate 2 peaks on capillary electrophoresis (1, pink and blue peaks). When these are the same (homozygous/shared, locus 2), this will generate only 1 peak (2, purple peak). B through D, Method for obtaining samples from formalin-fixed, paraffin embedded tissue sections. Areas of pure villous (marked V) and pure decidual (marked D) tissue are circled with a marking pen on a stained section (B). On a sequential unstained section, these foci are covered with a solution to facilitate removal from the slide (C, blue solution applied). These areas are carefully macrodissected from the tissue section (D, tissue removed in circled areas).

Figure 10

Methods for genotyping. A, Polymerase chain reaction amplification of short tandem repeat loci. Fluorescently labeled primers are used to amplify each locus to generate copies of the maternal and paternal alleles. When these are of different sizes (heterozygous, locus 1), this will generate 2 peaks on capillary electrophoresis (1, pink and blue peaks). When these are the same (homozygous/shared, locus 2), this will generate only 1 peak (2, purple peak). B through D, Method for obtaining samples from formalin-fixed, paraffin embedded tissue sections. Areas of pure villous (marked V) and pure decidual (marked D) tissue are circled with a marking pen on a stained section (B). On a sequential unstained section, these foci are covered with a solution to facilitate removal from the slide (C, blue solution applied). These areas are carefully macrodissected from the tissue section (D, tissue removed in circled areas).

Figure 11

Diagrams of molar entities with genotyping examples. A, Diagram of a villous structure from a complete hydatidiform mole demonstrates that the villus is composed of p57 androgenetic diploid cytotrophoblastic cells and p57 androgenetic diploid stromal cells. B, Per genotyping, all informative loci demonstrate that villous tissue contains only novel/paternal alleles (blue arrows) without maternal alleles (pink arrows), indicating a purely androgenetic conception. The presence of a single allele at all loci indicates a monospermic (homozygous) complete hydatidiform mole. C, Diagram of a villous structure from a partial hydatidiform mole demonstrates that the villus is composed of p57+ diandric triploid cytotrophoblastic cells and p57+ diandric triploid stromal cells. D, Per genotyping, 1 fully informative locus (CSF1PO) demonstrates that villous tissue contains a maternal allele (pink arrows) and a novel/paternal allele (blue arrow), with a paternal to maternal allele ratio of 2:1. All other loci are consistent with triploidy but are not fully informative because they do not establish the parental origins as a result of allele sharing (purple arrows). The combined findings indicate a diandric triploid conception, and the presence of 3 distinct alleles at 1 locus (VWA) in the setting of at least 1 locus establishing diandry (CSF1PO) indicates a dispermic (heterozygous) partial hydatidiform mole.

Figure 11

Diagrams of molar entities with genotyping examples. A, Diagram of a villous structure from a complete hydatidiform mole demonstrates that the villus is composed of p57 androgenetic diploid cytotrophoblastic cells and p57 androgenetic diploid stromal cells. B, Per genotyping, all informative loci demonstrate that villous tissue contains only novel/paternal alleles (blue arrows) without maternal alleles (pink arrows), indicating a purely androgenetic conception. The presence of a single allele at all loci indicates a monospermic (homozygous) complete hydatidiform mole. C, Diagram of a villous structure from a partial hydatidiform mole demonstrates that the villus is composed of p57+ diandric triploid cytotrophoblastic cells and p57+ diandric triploid stromal cells. D, Per genotyping, 1 fully informative locus (CSF1PO) demonstrates that villous tissue contains a maternal allele (pink arrows) and a novel/paternal allele (blue arrow), with a paternal to maternal allele ratio of 2:1. All other loci are consistent with triploidy but are not fully informative because they do not establish the parental origins as a result of allele sharing (purple arrows). The combined findings indicate a diandric triploid conception, and the presence of 3 distinct alleles at 1 locus (VWA) in the setting of at least 1 locus establishing diandry (CSF1PO) indicates a dispermic (heterozygous) partial hydatidiform mole.

Figure 12

Diagrams of nonmolar and mosaic entities with genotyping examples. A, Diagram of a villous structure from a nonmolar specimen demonstrates that the villus is composed of p57+ biparental diploid cytotrophoblastic cells and p57+ biparental diploid stromal cells. B, Per genotyping, fully informative loci demonstrate that villous tissue contains 1 maternal allele (pink arrows) and 1 novel/paternal allele (blue arrows) with allelic balance (paternal to maternal allele ratio of 1:1), indicating a biparental nonmolar conception. C, Diagram of a nonmolar androgenetic/biparental villous structure demonstrates that the villus is composed of p57+ biparental diploid cytotrophoblastic cells and p57 androgenetic diploid stromal cells. Villi of this type can represent an entire specimen (nonmolar form of androgenetic/biparental conception) or can be accompanied by a purely androgenetic villous component in which some villi are composed of p57 androgenetic diploid cytotrophoblastic cells and p57 androgenetic diploid stromal cells (androgenetic/biparental mosaic conception with a molar component; mixture of villous types shown in Figures 11, A, and 12, C). D, When genotyping is performed on the mixture of cell lines in the nonmolar mosaic villi (D, middle), several informative loci show that villous tissue contains both maternal alleles (pink arrows) and novel/paternal alleles (blue arrows), with a paternal to maternal allele ratios of >2:1. In conjunction with the p57 staining pattern indicating a mixture of p57 (purely androgenetic) villous stromal cells and p57+ (biparental) cytotrophoblastic cells (see Figure 8, B through D, for histology), and fluorescence in situ hybridization (FISH) results indicating that all villous stromal cells and cytotrophoblastic cells are diploid (data not shown), these ratios reflect an enrichment for paternal alleles attributable to the mixture of purely androgenetic cells with 2 paternal alleles and biparental cells with 1 paternal and 1 maternal allele. For the molar component (D, lower) which is uniformly p57 (see Figure 8, E through H, for histology) and also has uniformly diploid cells per FISH analysis (data not shown), several informative loci demonstrate that villous tissue contains only paternal alleles, consistent with a purely androgenetic molar (complete hydatidiform mole) component.

Figure 12

Diagrams of nonmolar and mosaic entities with genotyping examples. A, Diagram of a villous structure from a nonmolar specimen demonstrates that the villus is composed of p57+ biparental diploid cytotrophoblastic cells and p57+ biparental diploid stromal cells. B, Per genotyping, fully informative loci demonstrate that villous tissue contains 1 maternal allele (pink arrows) and 1 novel/paternal allele (blue arrows) with allelic balance (paternal to maternal allele ratio of 1:1), indicating a biparental nonmolar conception. C, Diagram of a nonmolar androgenetic/biparental villous structure demonstrates that the villus is composed of p57+ biparental diploid cytotrophoblastic cells and p57 androgenetic diploid stromal cells. Villi of this type can represent an entire specimen (nonmolar form of androgenetic/biparental conception) or can be accompanied by a purely androgenetic villous component in which some villi are composed of p57 androgenetic diploid cytotrophoblastic cells and p57 androgenetic diploid stromal cells (androgenetic/biparental mosaic conception with a molar component; mixture of villous types shown in Figures 11, A, and 12, C). D, When genotyping is performed on the mixture of cell lines in the nonmolar mosaic villi (D, middle), several informative loci show that villous tissue contains both maternal alleles (pink arrows) and novel/paternal alleles (blue arrows), with a paternal to maternal allele ratios of >2:1. In conjunction with the p57 staining pattern indicating a mixture of p57 (purely androgenetic) villous stromal cells and p57+ (biparental) cytotrophoblastic cells (see Figure 8, B through D, for histology), and fluorescence in situ hybridization (FISH) results indicating that all villous stromal cells and cytotrophoblastic cells are diploid (data not shown), these ratios reflect an enrichment for paternal alleles attributable to the mixture of purely androgenetic cells with 2 paternal alleles and biparental cells with 1 paternal and 1 maternal allele. For the molar component (D, lower) which is uniformly p57 (see Figure 8, E through H, for histology) and also has uniformly diploid cells per FISH analysis (data not shown), several informative loci demonstrate that villous tissue contains only paternal alleles, consistent with a purely androgenetic molar (complete hydatidiform mole) component.

DNA genotyping can greatly improve the diagnosis of hydatidiform mole, but interpretive challenges and unusual scenarios exist that require the careful correlation of morphology, p57 results, and genotyping data. These include the following:

  1. Specimens in which only villous tissue is available for analysis. Lack of maternal decidual tissue precludes determination of the parental source of polymorphic alleles and their ratios. In this situation, analysis of the villous tissue can yield results for which allelic balance and triploidy can be discerned, but the parental contributions cannot be determined without comparison of the patterns in the villous and decidual tissues. Thus, a nonmolar biparental pattern with allelic balance cannot be distinguished from the heterozygous form of purely androgenetic molar conception, and diandric versus digynic triploidy cannot be distinguished. The information obtained from the analysis would be essentially identical to that obtained with karyotyping, ploidy, or fluorescence in situ hybridization analysis. However, even without the maternal tissue control, the presence of homozygosity at all STR loci in villous tissue establishes a diagnosis of a homozygous androgenetic CHM. In this situation, androgenicity is inferred (because alleles cannot be confirmed as nonmaternal) and supported because this pattern is only obtained in purely androgenetic conceptions (when sufficient loci are tested, nonmolar conceptions never have purely homozygous loci).

  2. Mosaic conceptions, particularly those with a molar component (CHM). The presence of 2 morphologically distinct populations of villi (mosaic villi without trophoblastic hyperplasia and molar villi with trophoblastic hyperplasia) can lead to misclassification as a PHM. In addition, failure to recognize the discordant p57 expression pattern in some villi (often the majority) and the p57 molar component (which can be focal) contributes to misinterpretation as a p57+ PHM. These can generate complicated genotyping results, which can be challenging to interpret, particularly when the different villous components of the molar form are admixed in tested samples or when one of the cell lines is not diploid.31,34  Recognition of the different p57 staining patterns in mosaic molar conceptions is necessary for specific macrodissection of the distinct villous components to ensure accurate genotyping and correct interpretation of these complex specimens.

  3. Individual, double, and rare multiple trisomies. These have the potential to be interpreted erroneously as triploidy if a sufficient number of informative loci are not evaluated, resulting in misclassification as a diandric triploid PHM if the extra chromosomes are paternal in origin.12 

  4. Rare cases of biparental CHMs. These share morphology and lack of p57 expression with typical androgenetic CHMs, but the DNA genotyping result of biparental diploidy could be misinterpreted as a nonmolar conception in the absence of correlation with morphologic features and p57 results.

  5. Rare CHMs with aberrant retained p57 expression due to a retained maternal chromosome 11 (maternally derived trisomy of chromosome 11 in the setting of an otherwise purely androgenetic conception).75,76 

  6. Rare PHMs with aberrant loss of p57 expression due to loss of the maternal copy of chromosome 11.19,77 

  7. Complete hydatidiform moles occurring in the setting of a twin/multiple gestation. Failure to recognize the morphologically and immunohistochemically distinct villous populations can lead to incorrect interpretation as a PHM (“2” populations of villi, with some being p57+) and false assurance that a CHM has been excluded because of p57 positivity in at least some villi. Similar to mosaic specimens, recognition of 2 populations of villi with different p57 staining patterns is critical for accurate genotyping and interpretation of results.

  8. Donor egg conceptions. Lack of clinical history and failure to correlate morphology and p57 results with genotyping results can lead to misinterpretation of a nonmolar specimen as a heterozygous/dispermic CHM on the basis of genotyping data alone.78 

ALGORITHMIC APPROACH TO DIAGNOSIS OF HYDATIDIFORM MOLES

Algorithmic approaches using ancillary techniques applicable to formalin-fixed, paraffin-embedded tissues have been proposed for refining the diagnosis of hydatidiform moles.14,19,64,72,79  Reproducibility studies demonstrate that routine microscopic evaluation without use of ancillary techniques, even in the hands of gynecologic pathologists and even when a consensus diagnosis is used, leads to incorrect classification of at least 20% of cases.40,41  This suggests that there are inherent limitations in the ability of morphologic assessment to provide an accurate diagnosis of all cases, which is likely related to the known morphologic overlap of the entities and the lack of fully developed morphologic features in early examples. Given that experienced gynecologic pathologists already have subspecialty training and focused practice in gynecologic pathology, it is unlikely that there is any way to improve diagnosis using traditional morphologic (hematoxylin-eosin) assessment alone. Thus, use of an algorithmic approach that combines p57 immunohistochemistry and DNA genotyping for improving the diagnosis of hydatidiform moles is recommended (Figure 13).

Figure 13

Algorithmic approach to diagnosis of hydatidiform moles. Per one approach, potentially molar specimens are universally subjected to immunohistochemical analysis of p57 expression, with triage to genotyping based on this result. The p57 cases are diagnosed as complete hydatidiform mole, and p57+ cases are genotyped to distinguish partial hydatidiform moles from nonmolar specimens. In another approach, potentially molar specimens are universally subjected to genotyping. In yet another approach, some triage to p57 immunohistochemistry versus genotyping is performed based on morphologic assessment as favoring complete hydatidiform mole versus partial hydatidiform mole, respectively.

Figure 13

Algorithmic approach to diagnosis of hydatidiform moles. Per one approach, potentially molar specimens are universally subjected to immunohistochemical analysis of p57 expression, with triage to genotyping based on this result. The p57 cases are diagnosed as complete hydatidiform mole, and p57+ cases are genotyped to distinguish partial hydatidiform moles from nonmolar specimens. In another approach, potentially molar specimens are universally subjected to genotyping. In yet another approach, some triage to p57 immunohistochemistry versus genotyping is performed based on morphologic assessment as favoring complete hydatidiform mole versus partial hydatidiform mole, respectively.

The proposed approaches use standard histology for morphologic evaluation to select tissue for analysis and advocate genotyping as the preferred molecular technique (use of less specific techniques, such as flow cytometric DNA ploidy analysis or fluorescence in situ hybridization, is discouraged). One approach uses universal assessment of p57 expression by immunohistochemistry for all potentially molar specimens, with triage to genotyping based on the p57 result. If the morphologic features suggest a CHM and the p57 immunostain is negative (with satisfactory internal positive control), a diagnosis of CHM can be confidently established (with rare exceptions19,77 ). Analysis of p57 expression by immunohistochemistry is highly reproducible and is a technique that can be performed in most immunohistochemistry laboratories without the need for highly specialized equipment and expertise, such as that required for genotyping. DNA genotyping can confirm a diagnosis of CHM for a p57 specimen by demonstrating a purely androgenetic DNA pattern but is not necessary for routine diagnosis, provided the p57 result is satisfactory. If the clinical scenario suggests a recurrent familial case, then genotyping would be indicated to establish a diagnosis of a biparental rather than androgenetic CHM. If the p57 immunostain is positive, then a CHM has been excluded (with rare exceptions75,76 ). For p57+ cases, DNA genotyping is required to definitively distinguish a PHM from a nonmolar specimen. When the molecular analysis reveals a diandric triploid result, a diagnosis of a PHM is established. When genotyping yields a biparental conception with allelic balance or a digynic triploid result, then a diagnosis of a nonmolar specimen is established. Another approach uses universal genotyping based on morphologic assessment suggesting any kind of hydatidiform mole, with selective application of p57 immunohistochemistry to address any discordance between morphology and genotyping. In this approach, p57 immunohistochemistry is used only when there is a discrepancy between the morphology and the genotyping result (eg, rare cases of familial biparental CHMs, mosaicism, or CHM in a twin gestation).

In laboratories with experience and excellent technical support, these approaches yield a definitive diagnosis in a very high proportion of cases.19  These approaches are advocated when there is any suspicion for a hydatidiform mole, which includes either a clinical concern for a hydatidiform mole (eg, abnormally elevated β-hCG level, abnormal ultrasound findings, clinical diagnosis of “rule out molar pregnancy,” etc) or pathologic concern because of some morphologic abnormality of chorionic villi. Use of the p57 triage method represents a compromise between traditional morphologic assessment alone, which has limitations, and genotyping of all cases, which is clearly costlier. The p57 component of the algorithm should capture essentially all CHMs, the most important group to readily identify for clinical management purposes. Because PHMs have a low but real risk of persistent GTD and are managed as molar pregnancies per current guidelines (sometimes with abbreviated follow-up relative to management of CHMs),80,81  and because overdiagnosis of nonmolar specimens as PHMs has implications for infertility patients, genotyping of all p57+ potentially molar specimens per the algorithm provides for a definitive distinction of PHMs and nonmolar specimens, allowing for refined management of these entities. In the setting of limited resources, use of ancillary techniques can be focused on identifying the entity with the greatest risk for persistent GTD, namely, CHMs, by selectively applying only p57 immunohistochemistry to assist in diagnosing CHMs and foregoing genotyping for distinction of PHMs from nonmolar specimens. For the latter situation, an equivocal diagnosis, such as “abnormal villous morphology, PHM cannot be excluded,” might need to be rendered. Because the risk of persistent GTD for PHMs is much closer to that of nonmolar specimens than that of CHMs, this may well be acceptable for routine practice, with the understanding that an equivocal diagnosis will potentially lead to clinical management as a PHM at least for some abbreviated time frame, and that this approach does have accompanying costs (clinic visit, multiple serum β-hCG levels, contraception) which might well rival the cost of genotyping. With such a limited approach, it also needs to be understood that an apparently unequivocal diagnosis of either PHM or a nonmolar specimen established on the basis of morphologic assessment alone is not guaranteed to be accurate, even when rendered by an experienced gynecologic pathologist. Therefore, given the established suboptimal performance of morphologic assessment alone, even for experienced gynecologic pathologists, the most ideal method of correctly classifying all hydatidiform moles and nonmolar specimens is a combined approach including correlation of morphologic features, p57 immunohistochemistry, and DNA genotyping. In investigational pursuits, all molar specimens should be evaluated with ancillary techniques to ensure the rigorous classification of cases, particularly when designed to ascertain risk of persistent GTD associated with the various subtypes of hydatidiform moles.

SUMMARY

Studies using genotyping to establish true gold standard diagnoses have confirmed that morphologic diagnosis of hydatidiform moles continues to be negatively impacted by interobserver diagnostic variability both in routine and specialized gynecologic pathology practice. Diagnostic variability compromises investigations of the epidemiology, pathogenesis, and behavior of hydatidiform moles by using inaccurately classified cases. The modern approach to diagnosis of hydatidiform moles should require integration of ancillary techniques, particularly p57 immunohistochemistry and DNA genotyping, into routine practice as much as possible, with the goals of providing refined diagnosis, accurate assessment of the risk of persistent GTD associated with different subtypes of hydatidiform moles, and the appropriate guidance of clinical management.

References

1
Hui
P
,
Buza
N
,
Murphy
KM
,
Ronnett
BM
.
Hydatidiform moles: genetic basis and precision diagnosis
.
Annu Rev Pathol
.
2017
;
12
:
449
485
.
2
Sebire
NJ
,
Fisher
RA
,
Rees
HC
.
Histopathological diagnosis of partial and complete hydatidiform mole in the first trimester of pregnancy
.
Pediatr Dev Pathol
.
2003
;
6
(
1
):
69
77
.
3
Sebire
NJ
,
Makrydimas
G
,
Agnantis
NJ
,
Zagorianakou
N
,
Rees
H
,
Fisher
RA
.
Updated diagnostic criteria for partial and complete hydatidiform moles in early pregnancy
.
Anticancer Res
.
2003
;
23
(
2C
):
1723
1728
.
4
Szulman
AE
,
Surti
U.
The syndromes of hydatidiform mole, II: morphologic evolution of the complete and partial mole
.
Am J Obstet Gynecol
.
1978
;
132
(
1
):
20
27
.
5
Keep
D
,
Zaragoza
MV
,
Hassold
T
,
Redline
RW
.
Very early complete hydatidiform mole
.
Hum Pathol
.
1996
;
27
(
7
):
708
713
.
6
Fukunaga
M.
Histopathologic study of partial hydatidiform moles and DNA triploid placentas
.
Pathol Int
.
1994
;
44
(
7
):
528
534
.
7
Fukunaga
M.
Early partial hydatidiform mole: prevalence, histopathology, DNA ploidy, and persistence rate
.
Virchows Arch
.
2000
;
437
(
2
):
180
184
.
8
Genest
DR
.
Partial hydatidiform mole: clinicopathological features, differential diagnosis, ploidy and molecular studies, and gold standards for diagnosis
.
Int J Gynecol Pathol
.
2001
;
20
(
4
):
315
322
.
9
Buza
N
,
Hui
P.
Partial hydatidiform mole: histologic parameters in correlation with DNA genotyping
.
Int J Gynecol Pathol
.
2013
;
32
(
3
):
307
315
.
10
Bynum
J
,
Murphy
KM
,
DeScipio
C
, et al.
Invasive complete hydatidiform moles: analysis of a case series with genotyping
.
Int J Gynecol Pathol
.
2016
;
35
(
2
):
134
141
.
11
Chew
SH
,
Perlman
EJ
,
Williams
R
,
Kurman
RJ
,
Ronnett
BM
.
Morphology and DNA content analysis in the evaluation of first trimester placentas for partial hydatidiform mole (PHM)
.
Hum Pathol
.
2000
;
31
(
8
):
914
924
.
12
Norris-Kirby
A
,
Hagenkord
JM
,
Kshirsagar
M
,
Ronnett
BM
,
Murphy
KM
.
Abnormal villous morphology associated with triple trisomy of paternal origin
.
J Mol Diagn
.
2010
;
12
(
4
):
525
529
.
13
Redline
RW
,
Hassold
T
,
Zaragoza
M.
Determinants of villous trophoblastic hyperplasia in spontaneous abortions
.
Mod Pathol
.
1998
;
11
(
8
):
762
768
.
14
Ronnett
BM
,
DeScipio
C
,
Murphy
KM
.
Hydatidiform moles: ancillary techniques to refine diagnosis
.
Int J Gynecol Pathol
.
2011
;
30
(
2
):
101
116
.
15
Sebire
NJ
,
May
PC
,
Kaur
B
,
Seckl
MJ
,
Fisher
RA
.
Abnormal villous morphology mimicking a hydatidiform mole associated with paternal trisomy of chromosomes 3,7,8 and unipaternal disomy of chromosome 11
.
Diagn Pathol
.
2016
;
11
:
20
.
16
Kajii
T
,
Ohama
K.
Androgenetic origin of hydatidiform mole
.
Nature
.
1977
;
268
(
5621
):
633
634
.
17
Jacobs
PA
,
Wilson
CM
,
Sprenkle
JA
,
Rosenshein
NB
,
Migeon
BR
.
Mechanism of origin of complete hydatidiform moles
.
Nature
.
1980
;
286
(
5774
):
714
716
.
18
Lawler
SD
,
Povey
S
,
Fisher
RA
,
Pickthall
VJ
.
Genetic studies on hydatidiform moles, II: the origin of complete moles
.
Ann Hum Genet
.
1982
;
46
(
pt 3
):
209
222
.
19
Banet
N
,
DeScipio
C
,
Murphy
KM
, et al.
Characteristics of hydatidiform moles: analysis of a prospective series with p57 immunohistochemistry and molecular genotyping
.
Mod Pathol
.
2014
;
27
(
2
):
238
254
.
20
Ohama
K
,
Kajii
T
,
Okamoto
E
, et al.
Dispermic origin of XY hydatidiform moles
.
Nature
.
1981
;
292
(
5823
):
551
552
.
21
Murdoch
S
,
Djuric
U
,
Mazhar
B
, et al.
Mutations in NALP7 cause recurrent hydatidiform moles and reproductive wastage in humans
.
Nat Genet
.
2006
;
38
(
3
):
300
302
.
22
Parry
DA
,
Logan
CV
,
Hayward
BE
, et al.
Mutations causing familial biparental hydatidiform mole implicate c6orf221 as a possible regulator of genomic imprinting in the human oocyte
.
Am J Hum Genet
.
2011
;
89
(
3
):
451
458
.
23
Williams
D
,
Hodgetts
V
,
Gupta
J.
Recurrent hydatidiform moles
.
Eur J Obstet Gynecol Reprod Biol
.
2010
;
150
(
1
):
3
7
.
24
Lawler
SD
,
Fisher
RA
,
Pickthall
VJ
,
Povey
S
,
Evans
MW
.
Genetic studies on hydatidiform moles, I: the origin of partial moles
.
Cancer Genet Cytogenet
.
1982
;
5
(
4
):
309
320
.
25
Jacobs
PA
,
Szulman
AE
,
Funkhouser
J
,
Matsuura
JS
,
Wilson
CC
.
Human triploidy: relationship between parental origin of the additional haploid complement and development of partial hydatidiform mole
.
Ann Hum Genet
.
1982
;
46
(
pt 3
):
223
231
.
26
Zaragoza
MV
,
Surti
U
,
Redline
RW
,
Millie
E
,
Chakravarti
A
,
Hassold
TJ
.
Parental origin and phenotype of triploidy in spontaneous abortions: predominance of diandry and association with the partial hydatidiform mole
.
Am J Hum Genet
.
2000
;
66
(
6
):
1807
1820
.
27
Murphy
KM
,
DeScipio
C
,
Wagenfuehr
J
, et al.
Tetraploid partial hydatidiform mole: a case report and review of the literature
.
Int J Gynecol Pathol
.
2012
;
31
(
1
):
73
79
.
28
Redline
RW
,
Hassold
T
,
Zaragoza
BS
.
Prevalence of the partial molar phenotype in triploidy of maternal and paternal origin
.
Hum Pathol
.
1998
;
29
(
5
):
505
511
.
29
Fisher
RA
,
Tommasi
A
,
Short
D
,
Kaur
B
,
Seckl
MJ
,
Sebire
NJ
.
Clinical utility of selective molecular genotyping for diagnosis of partial hydatidiform mole; a retrospective study from a regional trophoblastic disease unit
.
J Clin Pathol
.
2014
;
67
(
11
):
980
984
.
30
Fallahian
M
,
Sebire
NJ
,
Savage
PM
,
Seckl
MJ
,
Fisher
RA
.
Mutations in NLRP7 and KHDC3L confer a complete hydatidiform mole phenotype on digynic triploid conceptions
.
Hum Mutat
.
2013
;
34
(
2
):
301
308
.
31
Hoffner
L
,
Dunn
J
,
Esposito
N
,
Macpherson
T
,
Surti
U.
P57KIP2 immunostaining and molecular cytogenetics: combined approach aids in diagnosis of morphologically challenging cases with molar phenotype and in detecting androgenetic cell lines in mosaic/chimeric conceptions
.
Hum Pathol
.
2008
;
39
(
1
):
63
72
.
32
Hoffner
L
,
Parks
WT
,
Swerdlow
SH
,
Carson
JC
,
Surti
U.
Simultaneous detection of imprinted gene expression (p57(KIP2)) and molecular cytogenetics (FICTION) in the evaluation of molar pregnancies
.
J Reprod Med
.
2010
;
55
(
5–6
):
219
228
.
33
Kaiser-Rogers
KA
,
McFadden
DE
,
Livasy
CA
, et al.
Androgenetic/biparental mosaicism causes placental mesenchymal dysplasia
.
J Med Genet
.
2006
;
43
(
2
):
187
192
.
34
Lewis
GH
,
DeScipio
C
,
Murphy
KM
, et al.
Characterization of androgenetic/biparental mosaic/chimeric conceptions, including those with a molar component: morphology, p57 immunohistochemistry, molecular genotyping, and risk of persistent gestational trophoblastic disease
.
Int J Gynecol Pathol
.
2013
;
32
(
2
):
199
214
.
35
Conran
RM
,
Hitchcock
CL
,
Popek
EJ
, et al.
Diagnostic considerations in molar gestations
.
Hum Pathol
.
1993
;
24
(
1
):
41
48
.
36
Fukunaga
M
,
Katabuchi
H
,
Nagasaka
T
,
Mikami
Y
,
Minamiguchi
S
,
Lage
JM
.
Interobserver and intraobserver variability in the diagnosis of hydatidiform mole
.
Am J Surg Pathol
.
2005
;
29
(
7
):
942
947
.
37
Howat
AJ
,
Beck
S
,
Fox
H
, et al.
Can histopathologists reliably diagnose molar pregnancy?
J Clin Pathol
.
1993
;
46
(
7
):
599
602
.
38
Javey
H
,
Borazjani
G
,
Behmard
S
,
Langley
FA
.
Discrepancies in the histological diagnosis of hydatidiform mole
.
Br J Obstet Gynaecol
.
1979
;
86
(
6
):
480
483
.
39
Messerli
ML
,
Parmley
T
,
Woodruff
JD
,
Lilienfeld
AM
,
Bevilacqua
L
,
Rosenshein
NB
.
Inter- and intra-pathologist variability in the diagnosis of gestational trophoblastic neoplasia
.
Obstet Gynecol
.
1987
;
69
(
4
):
622
626
.
40
Vang
R
,
Gupta
M
,
Wu
LS
, et al.
Diagnostic reproducibility of hydatidiform moles: ancillary techniques (p57 immunohistochemistry and molecular genotyping) improve morphologic diagnosis
.
Am J Surg Pathol
.
2012
;
36
(
3
):
443
453
.
41
Gupta
M
,
Vang
R
,
Yemelyanova
AV
, et al.
Diagnostic reproducibility of hydatidiform moles: ancillary techniques (p57 immunohistochemistry and molecular genotyping) improve morphologic diagnosis for both recently trained and experienced gynecologic pathologists
.
Am J Surg Pathol
.
2012
;
36
(
12
):
1747
1760
.
42
Kerkmeijer
LG
,
Massuger
LF
,
Ten Kate-Booij
MJ
,
Sweep
FC
,
Thomas
CM
.
Earlier diagnosis and serum human chorionic gonadotropin regression in complete hydatidiform moles
.
Obstet Gynecol
.
2009
;
113
(
2, pt 1
):
326
331
.
43
Berkowitz
RS
,
Goldstein
DP
.
Diagnosis and management of the primary hydatidiform mole
.
Obstet Gynecol Clin North Am
.
1988
;
15
(
3
):
491
503
.
44
Berkowitz
RS
,
Tuncer
ZS
,
Bernstein
MR
,
Goldstein
DP
.
Management of gestational trophoblastic diseases: subsequent pregnancy experience
.
Semin Oncol
.
2000
;
27
(
6
):
678
685
.
45
Garner
EI
,
Goldstein
DP
,
Feltmate
CM
,
Berkowitz
RS
.
Gestational trophoblastic disease
.
Clin Obstet Gynecol
.
2007
;
50
(
1
):
112
122
.
46
Sebire
NJ
,
Fisher
RA
,
Foskett
M
,
Rees
H
,
Seckl
MJ
,
Newlands
ES
.
Risk of recurrent hydatidiform mole and subsequent pregnancy outcome following complete or partial hydatidiform molar pregnancy
.
BJOG
.
2003
;
110
(
1
):
22
26
.
47
Ngan
HY
,
Kohorn
EI
,
Cole
LA
, et al.
Trophoblastic disease
.
Int J Gynaecol Obstet
.
2012
;
119
(
suppl 2
):
S130
S136
.
48
Feltmate
CM
,
Growdon
WB
,
Wolfberg
AJ
, et al.
Clinical characteristics of persistent gestational trophoblastic neoplasia after partial hydatidiform molar pregnancy
.
J Reprod Med
.
2006
;
51
(
11
):
902
906
.
49
Hancock
BW
,
Nazir
K
,
Everard
JE
.
Persistent gestational trophoblastic neoplasia after partial hydatidiform mole incidence and outcome
.
J Reprod Med
.
2006
;
51
(
10
):
764
766
.
50
Wielsma
S
,
Kerkmeijer
L
,
Bekkers
R
,
Pyman
J
,
Tan
J
,
Quinn
M.
Persistent trophoblast disease following partial molar pregnancy
.
Aust N Z J Obstet Gynaecol
.
2006
;
46
(
2
):
119
123
.
51
Scholz
NB
,
Bolund
L
,
Nyegaard
M
, et al.
Triploidy–observations in 154 diandric cases
.
PLoS One
.
2015
;
10
(
11
):
e0142545
.
52
Seckl
MJ
,
Fisher
RA
,
Salerno
G
, et al.
Choriocarcinoma and partial hydatidiform moles
.
Lancet
.
2000
;
356
(
9223
):
36
39
.
53
Cheung
AN
,
Khoo
US
,
Lai
CY
, et al.
Metastatic trophoblastic disease after an initial diagnosis of partial hydatidiform mole: genotyping and chromosome in situ hybridization analysis
.
Cancer
.
2004
;
100
(
7
):
1411
1417
.
54
Palmieri
C
,
Fisher
RA
,
Sebire
NJ
, et al.
Placental site trophoblastic tumour arising from a partial hydatidiform mole
.
Lancet
.
2005
;
366
(
9486
):
688
.
55
Medeiros
F
,
Callahan
MJ
,
Elvin
JA
,
Dorfman
DM
,
Berkowitz
RS
,
Quade
BJ
.
Intraplacental choriocarcinoma arising in a second trimester placenta with partial hydatidiform mole
.
Int J Gynecol Pathol
.
2008
;
27
(
2
):
247
251
.
56
Ma
N
,
Litkouhi
B
,
Mannion
CM
.
FIGO stage III metastatic gestational choriocarcinoma developed from an antecedent partial hydatidiform molar pregnancy bearing a numerical chromosomal aberration 68, XX: a case report and literature review
.
Int J Gynecol Pathol
.
2016
;
35
(
2
):
162
166
.
57
Sebire
NJ
,
Foskett
M
,
Fisher
RA
,
Lindsay
I
,
Seckl
MJ
.
Persistent gestational trophoblastic disease is rarely, if ever, derived from non-molar first-trimester miscarriage
.
Med Hypotheses
.
2005
;
64
(
4
):
689
693
.
58
Castrillon
DH
,
Sun
D
,
Weremowicz
S
,
Fisher
RA
,
Crum
CP
,
Genest
DR
.
Discrimination of complete hydatidiform mole from its mimics by immunohistochemistry of the paternally imprinted gene product p57KIP2
.
Am J Surg Pathol
.
2001
;
25
(
10
):
1225
1230
.
59
Chilosi
M
,
Piazzola
E
,
Lestani
M
, et al.
Differential expression of p57kip2, a maternally imprinted cdk inhibitor, in normal human placenta and gestational trophoblastic disease
.
Lab Invest
.
1998
;
78
(
3
):
269
276
.
60
Crisp
H
,
Burton
JL
,
Stewart
R
,
Wells
M.
Refining the diagnosis of hydatidiform mole: image ploidy analysis and p57KIP2 immunohistochemistry
.
J Urol
.
2003
;
43
(
4
):
363
373
.
61
Fukunaga
M.
Immunohistochemical characterization of p57(KIP2) expression in early hydatidiform moles
.
Hum Pathol
.
2002
;
33
(
12
):
1188
1192
.
62
Fukunaga
M.
Immunohistochemical characterization of p57Kip2 expression in tetraploid hydropic placentas
.
Arch Pathol Lab Med
.
2004
;
128
(
8
):
897
900
.
63
Jun
SY
,
Ro
JY
,
Kim
KR
.
p57kip2 is useful in the classification and differential diagnosis of complete and partial hydatidiform moles
.
J Urol
.
2003
;
43
(
1
):
17
25
.
64
McConnell
TG
,
Murphy
KM
,
Hafez
M
,
Vang
R
,
Ronnett
BM
.
Diagnosis and subclassification of hydatidiform moles using p57 immunohistochemistry and molecular genotyping: validation and prospective analysis in routine and consultation practice settings with development of an algorithmic approach
.
Am J Surg Pathol
.
2009
;
33
(
6
):
805
817
.
65
Merchant
SH
,
Amin
MB
,
Viswanatha
DS
,
Malhotra
RK
,
Moehlenkamp
C
,
Joste
NE
.
p57KIP2 immunohistochemistry in early molar pregnancies: emphasis on its complementary role in the differential diagnosis of hydropic abortuses
.
Hum Pathol
.
2005
;
36
(
2
):
180
186
.
66
Popiolek
DA
,
Yee
H
,
Mittal
K
, et al.
Multiplex short tandem repeat DNA analysis confirms the accuracy of p57(KIP2) immunostaining in the diagnosis of complete hydatidiform mole
.
Hum Pathol
.
2006
;
37
(
11
):
1426
1434
.
67
Romaguera
RL
,
Rodriguez
MM
,
Bruce
JH
, et al.
Molar gestations and hydropic abortions differentiated by p57 immunostaining
.
Fetal Pediatr Pathol
.
2004
;
23
(
2–3
):
181
190
.
68
Sarmadi
S
,
Izadi-Mood
N
,
Abbasi
A
,
Sanii
S.
p57KIP2 immunohistochemical expression: a useful diagnostic tool in discrimination between complete hydatidiform mole and its mimics
.
Arch Gynecol Obstet
.
2011
;
283
(
4
):
743
748
.
69
Bell
KA
,
Van Deerlin
V
,
Addya
K
,
Clevenger
CV
,
Van deerlin PG, Leonard DG. Molecular genetic testing from paraffin-embedded tissue distinguishes nonmolar hydropic abortion from hydatidiform mole
.
Mol Diagn
.
1999
;
4
(
1
):
11
19
.
70
Bifulco
C
,
Johnson
C
,
Hao
L
,
Kermalli
H
,
Bell
S
,
Hui
P.
Genotypic analysis of hydatidiform mole: an accurate and practical method of diagnosis
.
Am J Surg Pathol
.
2008
;
32
(
3
):
445
451
.
71
Murphy
KM
,
McConnell
TG
,
Hafez
MJ
,
Vang
R
,
Ronnett
BM
.
Molecular genotyping of hydatidiform moles: analytic validation of a multiplex short tandem repeat assay
.
J Mol Diagn
.
2009
;
11
(
6
):
598
605
.
72
Murphy
KM
,
Ronnett
BM
.
Molecular analysis of hydatidiform moles: utilizing p57 immunohistochemistry and molecular genotyping to refine morphologic diagnosis
.
Pathol Case Rev
.
2010
;
15
:
126
134
.
73
Lai
CY
,
Chan
KY
,
Khoo
US
, et al.
Analysis of gestational trophoblastic disease by genotyping and chromosome in situ hybridization
.
Mod Pathol
.
2004
;
17
(
1
):
40
48
.
74
Lipata
F
,
Parkash
V
,
Talmor
M
, et al.
Precise DNA genotyping diagnosis of hydatidiform mole
.
Obstet Gynecol
.
2010
;
115
(
4
):
784
794
.
75
Fisher
RA
,
Nucci
MR
,
Thaker
HM
,
Weremowicz
S
,
Genest
DR
,
Castrillon
DH
.
Complete hydatidiform mole retaining a chromosome 11 of maternal origin: molecular genetic analysis of a case
.
Mod Pathol
.
2004
;
17
(
9
):
1155
1160
.
76
McConnell
TG
,
Norris-Kirby
A
,
Hagenkord
JM
,
Ronnett
BM
,
Murphy
KM
.
Complete hydatidiform mole with retained maternal chromosomes 6 and 11
.
Am J Surg Pathol
.
2009
;
33
(
9
):
1409
1415
.
77
DeScipio
C
,
Haley
L
,
Beierl
K
,
Pandit
AP
,
Murphy
KM
,
Ronnett
BM
.
Diandric triploid hydatidiform mole with loss of maternal chromosome 11
.
Am J Surg Pathol
.
2011
;
35
(
10
):
1586
1591
.
78
Buza
N
,
Hui
P.
Egg donor pregnancy: a potential pitfall in DNA genotyping diagnosis of hydatidiform moles
.
Int J Gynecol Pathol
.
2014
;
33
(
5
):
507
510
.
79
Buza
N
,
Hui P.
Immunohistochemistry
and other ancillary techniques in the diagnosis of gestational trophoblastic diseases
.
Semin Diagn Pathol
.
2014
;
31
(
3
):
223
232
.
80
Soper
JT
,
Mutch
DG
,
Schink
JC
.
Diagnosis and treatment of gestational trophoblastic disease: ACOG Practice Bulletin No. 53
.
Gynecol Oncol
.
2004
;
93
(
3
):
575
585
.
81
Berkowitz
RS
,
Goldstein
DP
.
Clinical practice: molar pregnancy
.
N Engl J Med
.
2009
;
360
(
16
):
1639
1645
.

Author notes

Supplemental digital content is available for this article at www.archivesofpathology.org in the December 2018 table of contents.

The author has no relevant financial interest in the products or companies described in this article.

Presented in part at the 4th Princeton Integrated Pathology Symposium; April 23, 2017; Plainsboro, New Jersey.

Supplementary data