Abstract

Malignant deciduoid mesothelioma, a rare phenotype of epithelioid mesothelioma, arises more commonly from the peritoneum of young women, but it is also reported in the pleura of elderly people. We report a case of malignant deciduoid mesothelioma that occurred in a 41-year-old woman after cesarean section and was initially misdiagnosed as pseudotumoral deciduosis. Microscopically, the tumor was entirely composed of deciduoid areas, and only scattered tumor cells were positive for calretinin and keratin 5/6. The patient died 14 months after the first operation. This observation confirms the poor prognosis of this entity and the importance of the differential diagnosis of pseudotumoral deciduosis.

Malignant deciduoid mesothelioma (MDM) is a recently characterized variant of epithelial malignant mesothelioma that closely simulates exuberant ectopic decidual reaction. It was first described by Nascimento et al1 in 1994 in the peritoneum of young women, but further observations have also indicated its presence in the pleura and in elderly people.2–4 This unusual subtype of malignant mesothelioma is extremely rare, and to our knowledge, only 29 cases have been reported in the literature.5 We report a case of MDM in a 41-year-old woman that was revealed 6 weeks after cesarean section and initially misdiagnosed as pseudotumoral deciduosis.

REPORT OF A CASE

A previously healthy 41-year-old woman with an unremarkable medical history complained of abdominal pain 6 weeks after undergoing a cesarean section. There was no history of asbestos exposure in the patient or her family. At surgery, there was 900 mL of ascites. Numerous micronodules that affected the peritoneal cavity, omentum, and surface of the uterus and ovaries were observed. The intraoperative appearance suggested peritoneal carcinomatosis, and the patient underwent a total abdominal hysterectomy, bilateral salpingo-oophorectomy, and omentectomy. The diagnosis of pseudotumoral deciduosis was initially rendered, and no treatment was administered.

There was a short remission period following the surgery, but the patient complained of recurrent abdominal pain and a laparoscopy was performed. Two months later, she was referred to our hospital for the treatment of multiple intestinal fistulas.

Laboratory investigations showed an elevated CA 125 level (300 U/mL; reference range, <36 U/mL), but the other tumor markers, including serum β-human chorionic gonadotropin (βhCG) level, were within the reference ranges. Computed tomography revealed a heterogenous nodule of the parietal pleura that invaded the dermis, with osteolysis of the rib. This nodule was partially excised for histologic examination.

Two weeks later, a subsequent laparotomy showed loops of small bowel matted together and covered by numerous deposits of firm white tissue, which formed nodules and plaques both on the visceral and parietal peritoneal surface and in the Douglas cavity. A resection of the matted loops of small bowel was performed. The patient's condition gradually deteriorated, and she died 14 months after the onset of symptoms.

MATERIALS AND METHODS

All specimens were fixed in 10% buffered formalin and embedded in paraffin. Serial 4-μm-thick sections were stained with hematoxylin-eosin. Immunostaining was performed using antibodies for cytokeratin (KL1, Immunotech, Marseille, France), keratin 5/6 (Dako Corporation, Carpinteria, Calif), epithelial membrane antigen (Dako), vimentin (Dako), calretinin (Zymed, San Francisco, Calif), smooth muscle actin (Dako), desmin (Dako), S100 protein (Dako), CD15 (Immunotech), carcinoembryonic antigen (Dako), β-hCG (BioGenex, San Ramon, Calif), placental alkaline phosphatase (Dako), estrogen receptor (Dako), and progesterone receptor (BioGenex).

PATHOLOGIC FINDINGS

The thoracic nodule measured up to 3 cm and was white and firm. Microscopic examination revealed that this nodule was composed of large polygonal or ovoid cells with an abundant eosinophilic glassy cytoplasm with a sharp cellular outline, which contained a pleomorphic and vesicular nucleus with a single prominent nucleolus (Figure 1). Mitotic figures were rare, and the cytoplasm of some cells had an eccentric outer pale zone, which was sharply demarcated from a central glassy perinuclear region (Figure 1). Tumor cells were arranged in solid sheets and separated by a fibrous or loose edematous stroma, sometimes with hyalinized areas, either at the edge or within these sheets (Figure 2). There was partial tumor necrosis, and tumor cells invaded the dermis (Figure 2). Other typical patterns of the epithelial form of mesothelioma, such as papillary, tubular, or cordlike, were not observed in the numerous sections examined. The intestinal resection specimen showed sheets of deciduoid tumor cells that invaded the submucosa (Figure 3).

Figure 1.

Large polygonal cells with abundant eosinophilic cytoplasm, sharp cellular outlines, and a peripheral zone of cytoplasmic pallor. Nuclei are pleomorphic, with vesicular chromatin and a single prominent nucleolus. Rare mitotic figures are identified (hematoxylin-eosin, original magnification ×400). Figure 2. Tumor cells invading the dermis and separated by a hyalinized areas (hematoxylin-eosin, original magnification ×100). Figure 3. Tumor cells invading the intestinal submucosa (hematoxylin-eosin, original magnification ×50). Figure 4. Tumor cells are strongly positive for cytokeratin (KL1, original magnification ×200). Figure 5. Only scattered tumor cells are positive for keratin 5/6 (original magnification ×200). Figure 6. Only scattered tumor cells are positive for calretinin (original magnification ×400)

Figure 1.

Large polygonal cells with abundant eosinophilic cytoplasm, sharp cellular outlines, and a peripheral zone of cytoplasmic pallor. Nuclei are pleomorphic, with vesicular chromatin and a single prominent nucleolus. Rare mitotic figures are identified (hematoxylin-eosin, original magnification ×400). Figure 2. Tumor cells invading the dermis and separated by a hyalinized areas (hematoxylin-eosin, original magnification ×100). Figure 3. Tumor cells invading the intestinal submucosa (hematoxylin-eosin, original magnification ×50). Figure 4. Tumor cells are strongly positive for cytokeratin (KL1, original magnification ×200). Figure 5. Only scattered tumor cells are positive for keratin 5/6 (original magnification ×200). Figure 6. Only scattered tumor cells are positive for calretinin (original magnification ×400)

In the tumor cells, immunohistochemical analysis revealed diffuse and strong positivity for keratin (Figure 4) and vimentin and moderate positivity for epithelial membrane antigen. Only scattered tumor cells were positive for keratin 5/6 (Figure 5) and calretinin (Figure 6). All other stains, including germ cell markers and hormonal receptors, were negative. The diagnosis of MDM was made.

COMMENT

Malignant deciduoid mesothelioma was defined by Nascimento et al1 in 1994 as having a typically peritoneal site in young women, a highly aggressive behavior with a poor prognosis, and no etiologic correlation with asbestos. However, later reports have shown its presence in the pleura, in elderly people, and sometimes in association with asbestos exposure.5 

Malignant deciduoid mesothelioma apparently is rare, accounting for less than 5% of the mesotheliomas cases reviewed by Shia et al5 and for less than 2% reviewed by Ordonez.2 In contrast to classic mesothelioma, several features noted in patients with MDM are worth mentioning: its predilection to peritoneum (54% to 20%), the female preponderance (female-male ratio, 1.4:1), the young age of patients (40 years or younger), and the lower rate of asbestos exposure (35% to 80%).5 

The deciduoid morphologic features appear to be a spectrum from mesotheliomas of conventional appearance with focal deciduoid areas to mesotheliomas that are predominantly or possibly entirely, as in our case, deciduoid.3 In addition, MDMs are composed of a proliferation of large, round, ovoid, and polygonal cells with sharp cellular outlines, abundant glassy eosinophilic cytoplasm, and round vesicular nuclei with prominent eosinophilic nucleoli. Binucleation forms are occasionally present, but despite the cellular atypia and anaplasia, mitotic figures are infrequent.1–3 The cell cytoplasm is often more dense and darker around the nucleus and lighter at the periphery.5 The cells are arranged in anastomosing sheets or in small clusters, separated by a fibrous or loose edematous stroma. The histologic description of MDM was given by Talerman et al6 in 1985, when they reported the first case of this kind in a 13-year-old girl that, as in our case, was initially misdiagnosed as diffuse pseudotumoral deciduosis.

In our case, the diagnostic confusion between MDM and diffuse pseudotumoral deciduosis could have been avoided by careful study of the macroscopic and histologic features. Macroscopically, deciduosis, frequently described in pregnancy but also observed in the perimenarchal and postmenopausal periods, manifests as small discrete nodules or excrescences on the peritoneal surface and not as large, firm plaques and nodules. However, an occasional case of exuberant decidual reaction can give rise to bulky pseudotumoral lesions in which necrosis and cellular pleomorphism can be observed.7 The extensive involvement of the peritoneal cavity and the presence of ascites militate against the diagnosis of deciduosis. Microscopically, in deciduosis, the sheets of decidual cells are present within the connective tissue and do not usually affect its surface, as in the case of mesothelioma. In both entities, the cells have large amount of cytoplasm, but the nuclei differ considerably. The nuclei of the decidual cells are smaller and have dark clumped chromatin, whereas the nuclei of mesothelioma cells are vesicular with fine chromatin, prominent nucleolus, and occasional mitotic figures.2,4,6 The presence of typical areas of classic mesothelioma leads to the diagnosis. In our case, such areas were not discovered even after careful sampling of the specimen.

Immunohistochemical data appear not to be particularly useful in differentiating these 2 processes. Nascimento et al1 considered the negativity of deciduoid cells for cytokeratin to be significant. However, in a more recent study, Healthy et al8 reported a positivity for cytokeratin (AE1/3 and CAM 5.2) in 30% of extrapelvic deciduosis. Cytokeratin 5/6 has recently been reported as a sensitive and relatively specific positive finding in the diagnosis of mesothelioma, particularly when staining is strong and diffuse.3 Only scattered tumor cells were positive for this marker in our observation. Calretinin, a molecule considered sensitive and relatively specific for mesothelioma, was expressed in scattered tumor cells in our case. Riera et al9 found calretinin to lack sensitivity and to a lesser extent specificity. In fact, only 2 of 5 cases reported by Shia et al5 were positive for calretinin. Tumor cells in the case published by Orosz et al10 were also focally positive for this antibody. The diagnosis was made in these cases by ultrastructural study. The presence of numerous cytoplasmic intermediate filaments, either dispersed or bundled, appears to be the likely ultrastructural basis for the deciduoid histologic appearance.5 

From the prognostic point of view, MDMs are highly malignant; the mean survival time is 7.33 months (range, 1–21 months).5 A recent study11 of peritoneal malignant mesothelioma in women found that 40% of the patients survived longer than 4 years. The poor prognosis of our observation confirms the particularly aggressive nature of this entity.

Our case shows similar morphologic and clinical features to previously published examples of MDM that occurred in young women. We advocate distinguishing this clinicopathologic subtype of MDM from the deciduoid mesothelioma variant, which arises in the pleura and peritoneum of elderly individuals with a prior history of asbestos exposure. Further studies on a large number of cases may be helpful in more fully delineating the clinical and pathologic features of this rare variant of mesothelioma.

In summary, we report a case of MDM that occurred in a 41-year-old woman 6 weeks after cesarean section and was misinterpreted as pseudotumoral deciduosis. This case highlights the need of the pathologist to be aware of this subtype of malignant mesothelioma to avoid a misdiagnosis of a benign process. We share the opinion that MDM may still represent a distinct subtype of epithelioid mesothelioma, with specific clinical and pathologic features.

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The authors have no relevant financial interest in the products or companies described in this article.

Author notes

Corresponding author: Najat Mourra, MD, Service d'Anatomie Pathologique, Hôpital St-Antoine, 184 rue du faubourg St-Antoine, 75012 Paris, France (najat.mourra@sat.ap-hop-paris.fr)

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