Plasmablastic Lymphoma of the Cervical Lymph Nodes in a Human Immunodeficiency Virus–Negative Patient: A Case Report and Review of the Literature

Plasmablastic lymphoma (PBL) is a recently described subtype of diffuse large B-cell lymphoma, which occurs almost exclusively in patients infected with human immunodeficiency virus (HIV) and involves the oral cavity and jaw.1–6 This lymphoma is characterized by diffuse growth of large tumor cells with a high MIB-1 proliferation index, the presence of immunoglobulin heavy-chain gene rearrangement, and expression of the plasma cell– associated antigens CD38 and CD138. Typically, PBL lacks expression of leukocyte common antigen (LCA), CD19, and CD20. There is also frequently positivity for Epstein- Barr virus (EBV)–encoded RNA (EBER).1 Exceptional cases of PBL have been reported in the stomach, lung, and a variant of Richter syndrome.7–9 Recently, a case of PBL presenting as an isolated nasal cavity mass was reported.10 

We report an unusual clinical case of lymph node–based PBL. The results of tumor immunophenotyping and molecular analysis are reported and discussed in the context of the differential diagnosis. To the best of our knowledge, this is the first case report of PBL with initial presentation in a nodal site and with a dominant pattern of nodal involvement in an HIV-negative individual.

This 82-year-old man had a history of enlargement of a right neck mass that had been present for approximately 4 months and was referred to the ear, nose, and throat clinic at the Geisinger Medical Center (Danville, Pa). On physical examination, an 8.0- cm, firm, rubbery, fixed mass, and multiple small mobile nodules were identified in the right anterior upper neck. A fine-needle aspiration biopsy with flow cytometric study was performed as an initial workup, and a diagnosis of “positive for hematopoietic malignancy” was rendered. A subsequent incisional biopsy showed an unusual malignant hematopoietic tumor with CD38, CD138, CD30, epithelial membrane antigen (EMA), and lysozyme positivity. The MIB-1 index was high, and the tumor cells were positive with EBER probe by in situ hybridization. The tumor cells were negative for multiple B-cell and T-cell markers. The case was sent to Elaine Jaffe, MD, at the National Cancer Institute (Bethesda, Md) in consultation, and a diagnosis of EBV- positive, human herpesvirus 8–negative PBL was established.

Staging procedures revealed prominent lymphadenopathy in the right neck with an extension into the supraclavicular fossa, the mediastinum, and axilla, as well as splenomegaly. Bilateral bone marrow examinations were negative by light microscopy and flow cytometry. There was no monoclonal gammopathy. The patient had no HIV risk factors, and an HIV test was negative by enzyme-linked immunosorbent assay. Following the primary diagnosis of PBL, additional physical examination revealed a previously unrecognized gumline lesion, extending from the area of the first molar to the midline on the right upper jaw. The mucosa was thickened, white, and fleshy in appearance with a small area of superficial ulceration. Involvement by lymphoma was suspected, although no biopsy was taken.

The patient received 6 cycles of CHOP (cyclophosphamide, doxorubicin, vincristine, and prednisone) therapy and had a partial response (>50% reduction of the neck mass) to the treatment. The upper gumline lesion resolved with the treatment, reinforcing the clinical suspicion of involvement by lymphoma. However, at 6 months a computed tomographic scan showed no change in the mediastinal and hilar lymphadenopathy, more evidence of retroperitoneal adenopathy, a small left pleural effusion, a subpleural nodule, a new peripheral renal lesion, and persistent splenomegaly.

Direct smears of fine-needle aspirate were stained with Papanicolaou and Diff-Quik stains. Additional aspirate was procured in an RPMI solution and submitted for flow cytometric analysis.

Immunohistochemical stains were performed on both cytologic smears and formalin-fixed, paraffin-embedded tissue sections using the avidin-biotin-peroxidase complex method in a Dako autostainer (Dako Corporation, Carpinteria, Calif), according to a standard immunohistochemical staining protocol. The following antibodies were used: CD2, CD5, CD10, CD3, CD20, CD15, CD30, CD43, CD79a, CD56, EMA, LCA, S100, AE1/3, ALK-1, CD68, Ki-67, lysozyme (all from Dako), CD38 (Lab Vision/Neomarkers, Fremont, Calif), and CD138 (Sero Tec, Raleigh, NC). Tissues known to be positive or negative for the antibodies were used as controls.

In situ hybridization was performed on formalin-fixed, paraffin-embedded tissue sections with peptide nucleic acid probes complementary to 2 nuclear (EBER) transcripts (Dako), according to a standard protocol provided by Dako and a previously described method.11 

A fine-needle aspirate from the right cervical lymph node submitted in RPMI was studied by 2-color flow cytometry. The panel of antibodies (Beckman-Coulter Company, Marseille, France) included CD45–phycoerythrin–cyanine 5 (PC5), CD43–fluorescein isothiocyanate (FITC), CD3–phycoerythrin–Texas-Red-X (ECD), CD4-phycoerythrin (PE), CD8-FITC, CD10-PE, CD19-ECD, CD20-FITC, κ-FITC, λ-PE, CD14-FITC, HLA-DR–FITC, EMA- FITC, and control immunoglobulins. The analysis was completed in a flow cytometer (EPICS XL-MCL, Coulter, Miami, Fla).

Southern blot analysis was performed on frozen nodal tissue as previously described.12 The isolated DNA was digested with restriction endonuclease EcoRI, BamHI, and HindIII, respectively. Four α-³²P labeled DNA probes (Dako) were used in this study. They included (a) J_H probe (immunoglobulin heavy-chain joining region), (b) J_K probe (κ-light-chain joining region), (c) T-cell receptor (TCR) β probe (specific for Cβ1 and Cβ2 gene segments within the TCRβ locus on chromosome 7q34-7q35), and (d) TCRβJ2 probe (specific for the Jβ2.7 gene segment and the region 3′ within the TCRβ locus on chromosome 7q34-7q35).

The aspirates were composed of highly atypical large tumor cells lying in loosely cohesive groups and singles. The tumor cells had dense basophilic cytoplasm, slightly eccentrically located nuclei, and 1 to 2 prominent nucleoli, and some had fine cytoplasmic vacuoles (Figure 1). A mixed background population of benign lymphoid cells and scattered eosinophils was present. Flow cytometry of the aspirated cells demonstrated the large cells to be positive for EMA but negative for LCA, pan B- and T-cell surface markers, and κ and λ light chains. The smaller lymphoid cells in the sample were a mixture of heterogeneous T cells and activated polytypic B cells.

Immunocytochemical stains performed on the destained direct smears demonstrated that the atypical cells on the smears were negative for LCA, pancytokeratin (AE1/3), and S100. Owing to the limited sample available, we were unable to test for additional markers and an incisional biopsy was recommended.

Representative sections from the incisional biopsy specimen demonstrated a diffuse proliferation of large malignant cells with a total effacement of the normal lymphoid architecture. The malignant cells had large nuclei with 1 to 2 prominent nucleoli, scanty to moderate amounts of cytoplasm, and relatively smooth nuclear contours. Some of the malignant cells showed slightly eccentrically located nuclei (Figure 2). Many mitoses were present.

A panel of immunohistochemical stains showed the neoplastic cells to be positive for CD138, CD30, EMA, and lysozyme; focally positive for CD38; and negative for all other tested markers, including CD2, CD15, CD20, CD79a, and ALK-1. Figures 3 through 5 demonstrate CD138, CD30, and lysozyme positivity, respectively. The lysozyme staining in tumor cells was weak as compared to the heavy staining in histiocytes. Focally weak positivity for κ light chain was noted. Immunohistochemical stain for MIB-1 demonstrated positive nuclear staining in 60% of the tumor cells. A CD68 stain demonstrated a diffuse and prominent admixture of benign histiocytes or macrophages, which were negative for CD21, CD35, and S100.

In situ hybridization for EBER revealed diffuse and strongly positive nuclear staining (Figure 6).

Southern blot analysis after restriction endonuclease digestion with EcoRI, BamHI, and HindIII revealed germline bands at 9.3, 11.8, and 5.1 kilobases (kb), respectively, which were present in both the control placenta tissue and the patient sample. The patient's sample also demonstrated non-germline bands at 12.5 and 6.7 kb, 10.5 and 8.3 kb, and 7.0 and 1.75 kb following restriction enzyme digestion with EcoRI, BamHI and HindIII, respectively. These results indicate κ-light-chain gene rearrangement (Figure 7). No evidence of gene rearrangement was noted using JH, TCRβC, and TCRβJ2 probes.

In contrast to the previous reported cases, the current case has several unique features. First, it occurred in an HIV-negative patient; second, it initially presented as a nodal lymphoma; and third, it demonstrated κ-light-chain gene rearrangement instead of immunoglobulin heavy- chain gene rearrangement, as found in most of the previously reported cases. Finally, it showed positive immunohistochemical stains for CD30, EMA, and lysozyme. Immunohistochemical stains for CD30 and histiocytic markers were either not included or negative in the previously reported cases.1,6,13,14 

The differential diagnosis of PBL as encountered in this case included (a) other hematopoietic neoplasms, such as anaplastic large cell lymphoma (null cell type), plasmablastic multiple myeloma, Hodgkin lymphoma, and myeloid sarcoma; (b) metastatic carcinoma; and (c) metastatic melanoma.

Owing to the nodal presentation, positive staining for CD30 and EMA, and negative staining for B-cell and T- cell markers, anaplastic large cell lymphoma (null cell type) was within the differential diagnosis. On review, some of the malignant cells on the fine-needle aspiration biopsy specimen had eccentric nuclei with a suggestion of plasmacytoid differentiation. Classic anaplastic large cell lymphoma frequently shows a spectrum of neoplastic cells, ranging from small or intermediate-sized to pleomorphic and bizarre tumor cells. Ring nuclei suggest the diagnosis if present.15 Plasmacytoid differentiation is not a common feature of anaplastic large cell lymphoma. CD30 and EMA positivity are the important diagnostic criteria for anaplastic large cell lymphoma, but also can be observed in Hodgkin lymphoma, some carcinomas, and germ cell tumors. Therefore, additional markers, including CD38, CD138, κ and λ light chains, and gene rearrangement for immunoglobulin light chains and heavy chains, are useful in discriminating PBL from anaplastic lymphoma (null cell type).

Anaplastic large cell lymphoma kinase 1 (ALK-1) and the t(2;5) chromosomal translocation are useful in diagnosing anaplastic large cell lymphoma when present, but have been detected in only 30% to 60% of cases, depending on the methods used.16 Moreover, 3 cases of ALK-positive plasmablastic B-cell lymphoma associated with the t(2;5)(p23;q35) chromosomal translocation were reported in 2 recently published articles.13,14 By contrast, an analysis of TCR gene rearrangement should provide some important information, because nearly all cases of anaplastic large cell lymphomas, including null cell type, demonstrate a TCR rearrangement.17 

Anaplastic plasmacytoma/multiple myeloma may resemble a PBL. However, the neoplastic cells tend to have more abundant cytoplasm, eccentrically located nuclei, and binucleation or multinucleation. The immunophenotype may be similar to that of PBL, although the cells characteristically demonstrate strong cytoplasmic κ or λ staining, a low MIB-1 proliferation index, and negativity for EBER. In addition, bone marrow involvement and serum monoclonal protein are common findings.

The clinical presentation of localized lymphadenopathy, the cytologic findings of large atypical cells in a background of mixed lymphoid cells and eosinophils, and the immunohistochemical findings of CD30 positivity and LCA negativity, raised a possibility of a classic Hodgkin lymphoma. Classic Reed-Sternberg (R-S) cells were not identified in this case. One should be aware that R-S–like cells could be seen in other diseases. Therefore, a characteristic background of polymorphic lymphoid cells, plasma cells, and eosinophils should be present. On the other hand, classic R-S cells may not be easily identified; instead, a variant of mononuclear R-S cells may be the only neoplastic cells observed on the cytologic smears. Other immunohistochemical markers, including CD15, CD38, and CD138, are useful in making a definitive diagnosis.

Myeloid sarcoma may present a diagnostic dilemma. The findings of neoplastic cells with a very high nuclear- cytoplasmic ratio, fine blastic chromatin, and limited numbers of lymphoglandular bodies in the background are similar to the findings of PBL in this case. Attention should be paid to identification of eosinophilic myeloblasts. Furthermore, negative staining for myeloperoxidase, chloracetate esterase, CD43, CD34, and CD117 excludes the possibility of myeloid sarcoma.

The presence of neoplastic cells with abundant eosinophilic cytoplasm, binucleation, and intranuclear cytoplasm invaginations may suggest a diagnosis of melanoma. If there is any doubt, immunostains for S100, HMB-45, and Melan A will usually solve the problems.

The findings of loosely cohesive, large neoplastic cells in a background of lymphoid cells, in conjunction with negativity of the atypical large cells for LCA, T-cell and B- cell markers, and positivity for EMA, may mistakenly lead to a diagnosis of metastatic undifferentiated carcinoma in a fine-needle aspiration biopsy specimen. To avoid this potential pitfall, a broad-spectrum cytokeratin marker, such as AE1/3, should be included in the test panel.

In summary, this case report serves to broaden the reported clinical spectrum of PBL, which is usually an extranodal disease occurring in immunosuppressed patients. A detailed immunophenotypic study of this tumor was needed to establish the diagnosis of PBL, and revealed the expression of CD30 and lysozyme markers not reported previously for PBL. Given the clinical, immunophenotypic, and molecular signature of this tumor, our case may represent a unique variant of PBL.