Unusual lymphomas: Unusual sites

INTRODUCTION

Lymphomas, both Hodgkin’s and Non-Hodgkins, are malignant neoplasms of lymphocytes that usually involve lymph nodes, bone marrow, and extranodal sites.^[1] Non-Hodgkin’s lymphoma (NHL) is the most common hematological malignancy worldwide, and it refers to a group of heterogeneous B-cell and T-cell proliferation and natural killer (NK) cells.^[2]

Among these, follicular lymphoma (FL) and chronic lymphocytic leukemia (CLL) are more common NHLs in the Western population, whereas diffuse large B-cell lymphoma (DLBCL) is rapidly emerging as the most prevalent NHL in India.^[3] Outside the lineage specific lymphomas, gray zone lymphomas (GZLs) were first introduced in World Health Organization (WHO) classification as a distinct entity in 2008.^[4] The term GZLs are defined as lymphomas sharing features both that of classical Hodgkin’s lymphoma (CHL) and DLBCL. Despite advances in immunophenotyping, molecular diagnostics, and a precise morphological based discrimination, the diagnosis of GZL still remains complex.^[5] Initially, they were thought to arise primarily from mediastinum, but now further analyses indicate both mediastinal and systemic presentations. Regardless of the presentation of the patient, the GZLs have comparatively inferior survival rates to that of CHL or DLBCL.^[5]

Many lymphomas, however, still need to be treated aggressively and promptly, making the diagnosis quintessential.^[6] It is pertinent to note that the diagnostic algorithms are smoother in the case of nodal lymphomas and is challenging in cases presenting at unusual sites with unusual morphologies.^[7] Biopsy and immunohistochemistry remain the initial investigative modalities used to document the diagnosis.^[7] Thus, the histopathologist must be alert to the “not-so-common” lymphomas.^[8] In this article, we have tried to highlight and discuss some crucial categories of challenging lymphomas, wherein strictly guided by the “blue book,” we have arrived at a diagnosis; all these patients have responded to treatment.^[9]

CASE SERIES

Case 1

The first case was a 14-year-old male who underwent cervical lymph node dissection as a part of a diagnostic workup for generalized lymphadenopathy, fever, night sweats and malaise. The lymphadenopathy was present since 2 months and was unrelenting to therapy. What initially began as discrete nodes matted themselves into a large diffuse mass. On work up, computed tomography revealed that he had a mediastinal mass. However, due to ease of accessibility, he underwent a cervical nodal biopsy. The predominant morphological features were that of Hodgkin’s lymphoma. Focally, however, these cells were seen in a sheet-like arrangement. With immunohistochemistry, these cells were strongly positive for leukocyte common antigen (LCA), Cluster of differentiation (CD20), and CD30, along with a weak expression for Paired box 5 (PAX5). There were CD3 positive T cells rosetting around these large mononuclear Reed–Sternberg cells [Figure 1a-f]. A final diagnosis of B-cell lymphoma (BCL), unclassifiable with features intermediate between DLBCL and CHL, was rendered. This case was diagnosed neither as a Classical Hodgkin’s with CD20 positivity nor as a DLBCL with CD30 positivity in view of a strong reactivity for both these markers.

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Figure 1:

Histology and IHC of B-cell lymphoma unclassifiable, with features intermediate between diffuse large B-cell lymphoma and Classical Hodgkin’s Lymphoma. (a) Hematoxylin and eosin stained sections show diffuse effacement of architecture with prominence of Reed-Sternberg cells (10×). (b) Immunohistochemical stain for LCA is positive (10×). (c)Immunohistochemical stain for CD20 was positive (10×). (d) Immunohistochemical stain for CD3 was positive in surrounding T cells (10×). (e) Immunohistochemical stain for CD30 is positive (10×). (f) Immunohistochemical stain for PAX5 shows dim expression (10×). CD: Cluster of differentiation, LCA: Leucocyte common antigen, PAX 5: Paired box 5.

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Case 2

A 35-year-old male underwent axillary lymph node excision. On histology, there was diffuse effacement of architecture with prominence of small lymphoid cells in a vague nodular pattern. Interspersed among these cells were larger binucleate and multilobate cells reminiscent of popcorn-like cells of Hodgkin’s lymphoma (HL). These cells had small basophilic nucleoli and were intermixed with mature lymphocytes and plasma cells. On immunohistochemistry (IHC), the large cells were positive for LCA, CD20, BCL6, and PAX5. epithelial membrane antigen (EMA) positivity was noted. They were negative for epstein barr virus receptor (EBVR), CD15, and CD30. Further, an additional panel of IHC was performed using CD3, BCL2, and CD68. The tumor cells were positive for both BCL2 and CD68, and CD3 was positive in the lymphocytes surrounding the multilobate cells [Figure 2a-f]. Based on morphology and IHC, a diagnosis of nodular lymphocyte predominant HL (NLPHL) and T-cell/histiocyte-rich BCL was rendered.

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Figure 2:

Histology and IHC of NLPHL and T-cell/histiocyte-rich B-cell lymphoma. (a) Hematoxylin and eosin stained sections show diffuse effacement of architecture with prominence of small lymphoid cells in a vague nodular pattern. Interspersed among these cells were large binucleate and multilobate cells (10×). (b) Immunohistochemical stain for LCA is positive (4×). (c-e) Immunohistochemical stains for CD20 (10×), PAX5 (10×) and BCL2 (10×) were positive. (f) Immunohistochemical stain for CD30 was negative (10×). CD: Cluster of differentiation, LCA: Leukocyte common antigen, PAX 5: Paired box 5, BCL2: B-cell leukemia/lymphoma 2 protein.

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Case 3

A 22-year-old female underwent large bowel (ascending colon) resection due to subacute intestinal obstruction. Grossly, a tumor was seen centered in the submucosa, invading all the layers of the intestine with normal mucosal layer. The individual tumor cells were pleomorphic, often spindle-shaped, with irregular nuclear membrane and scant eosinophilic cytoplasm. The overlying mucosa was unremarkable. Based on morphology and initial IHC panel of Pan cytokeratin (CK), LCA, Synaptophysin, Chromogranin, EMA, and Vimentin yielded positivity for LCA, and a diagnosis of lymphoma was considered. A secondary panel of IHC including CD3, CD19, CD20, CD10, multiple myeloma oncogene-1 (MUM1), BCL2, BCL6, CD5, CD23, CD117, and CD138 was performed, of which the tumor cells showed uniform strong positivity for BCL2 and CD23 with a Kiel-67 (Ki67) index of 40% [Figure 3a-h]. Based on morphology and IHC, the possibility of follicular dendritic cell sarcoma was considered. This was an isolated lesion, and no associated nodal or extranodal disease was diagnosed.

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Figure 3:

Histology and IHC of follicular dendritic cell sarcoma (a) hematoxylin and eosin section shows tumor cells which appear pleomorphic, often spindle shaped with irregular nuclear membrane and scant eosinophilic cytoplasm. The overlying mucosa was unremarkable (4×). (b) Immunohistochemical stain for LCA is positive (10×). (c) Immunohistochemical stain for EMA is negative (20×). (d and e ) Immunohistochemical stain for CD20 (20×) and CD3 (20×) were both positive. (h) Ki67 labelling index was 40% (10×) Pan CK, Vimentin, CD117, and synaptophysin were all negative-not shown in the figure. CD: Cluster of differentiation, LCA: Leukocyte common antigen, Ki 67: Kiel-67, BCL2: B-cell leukemia/lymphoma 2 protein.

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Case 4

A 62-year-old female presented with a nasal cavity mass. On histopathology, fragments of soft tissue were seen infiltrated by the tumor cells in sheets. The tumor cells were small, with a hyperchromatic nucleus and scant cytoplasm. Extensive necrosis and karyorrhexis were noted throughout the tumor. A morphological diagnosis of nasopharyngeal carcinoma was made. The initial panel for IHC based on site and morphology was performed for LCA, CK, Vimentin, and Ki-67, revealing LCA positivity in large cells with a Ki67 index of more than 70%. Pan CK and Vimentin were negative. A secondary panel was done, including CD19, CD20, CD3, and CD5, all of which were negative [Figure 4a-h]. Based on morphology and IHC, a diagnosis of high-grade undifferentiated lymphoma was made. Tissue was too scant for any other IHC.

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Figure 4:

Histology and IHC of high-grade undifferentiated lymphoma. (a) hematoxylin and eosin stained section shows tumor cells with high degree of pleomorphism with prominent nucleoli (10×). (b) IHC for LCA is positive (10×). IHC for CD19 (10×), CD3 (40×), CD5 (40×), CD138 (40×) and CD30 all were negative (c-g from left to right). Ki 67 labelling index is > 70% (10×) (black arrows). CD: Cluster of differentiation, LCA: Leukocyte common antigen, Ki 67: Kiel-67.

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DISCUSSION

Lymphomas are broadly divided into two categories HL and NHL. HL is again further categorized into CHL and NLPHL. CHL is further subdivided into four subgroups: Nodular sclerosis HL, lymphocyte-rich HL, mixed cellularity HL, and lymphocyte depleted HL. With modern treatment protocols, the Hodgkin’s subtypes have lost most of their prognostic relevance.^[9] However, the WHO in its latest classification merits the continuity of describing these subtypes to supports the ongoing clinical trials and specific subtypes are associated with different clinical features and different biological pathways.^[9] Whereas CHL is characterized by the presence of large mononuclear, Hodgkin cell and multi-nucleated macronucleolar Reed–Sternberg cell which are usually surrounded by non-neoplastic T-cells in a background of inflammatory cells, the NLPHL lacks typical R-S cells. The reed sternberg (RS) cells show positive immunoexpression for CD30, CD15, and PAX-5 (attenuated) and are specifically LCA negative. On the other hand, positive IHC expression of LCA and CD20 is seen in neoplastic NLPHL cells. While NLPHL lacks the typical RS cells, it is characterized by a nodular or nodular and diffuse proliferation of small lymphocytes with singly scattered large neoplastic cells known as lymphocyte predominant (LP) or “Popcorn cells.” The LP cells or “Popcorn cells” are seen scattered singly amidst a nodular or diffuse proliferation of small lymphocytes in NLPHL. NLPHL has varied presentation occurring in cervical, axillary, or inguinal lymph nodes but can rarely arise in mesenteric lymph nodes unlike CHL which occurs more commonly in cervical lymph nodes. An important issue arises in NLPHL, in recognizing the different growth patterns [Table 1] overlapping with T-cell histiocyte rich large BCL (THRLBCL). These patterns occur across all age groups and patterns-C, D, and E have been associated with more aggressive behavior in clinical trials.^[10]

The morphology of NHLs is highly variable, and distinction into a specific lymphoma is based on the demonstration of IHC. The IHC panel used could be highly variable and might require the application of a gene profile whenever necessary.^[9]

The IHC panel discussion here is based on the categorization of NHLs into DLBCL and its variants: mature B-cell neoplasms other than DLBCL, T/NK cell neoplasms, and precursor lymphomas. Conventional IHC is used for DLBCL, and its variants include CD3, CD20, Ki-67, CD10, BCL-6, MUM-1, BCL-2, cellular MYC protooncogene, and Epstein Barr virus In-situ hybridisation (EBV ISH). The typical DLBCL-NOS is usually CD3 negative and CD20 positive, with a Ki67 index of more than 80%. The further categorization for the cell of origin is based on CD10, BCL6, and MUM-1. In the latest WHO classification, the names of some entities have been modified for reasons of consistency, from DLBCL to “large B-cell lymphoma,” acknowledging the fact that a diffuse growth pattern is either not apparent/present or cannot be assessed in some entities (e.g., fibrin-associated large BCL or fluid-overload associated large BCL). Furthermore, it is recommended to continue the categorization of the cell of origin into germinal center and non-germinal center (activated B-cell) types, even though the distinction between these is of little merit outside the clinical trials.^[11]

Among mature B-cell neoplasms outside DLBCL and its variants, here we discuss FL, CLL/small lymphocytic leukemia, marginal zone lymphoma (MZL), and Mantle cell lymphoma (MCL) [Table 2]. All these lymphomas express B-cell markers, namely, CD19, CD20, and CD79a. In the latest WHO classification, FL classification has undergone a revision from grading to grouping and is now grouped into Classical FL. FL with uncommon features due to the lack of consensus regarding the morphological spectrum of centroblasts and using conventional methods for counting has negatively impacted reproducibility.^[12-14] According to the latest WHO classification, MCL has been further categorized based on risk stratification into in situ mantle cell neoplasm, MCL, and non-nodal MCL.^[9] In the latest WHO classification, extranodal MZL (EMZL) and nodal MZL (NMZL) have been retained along with a separate entity designated as per cutaneous MZL (PCMZL).^[9] EMZL, NMZL, and PCMZL have overlapping histologic and immunophenotypic features: the neoplastic cells are mature small B cells typically negative for CD5 and CD10. Plasmocytic differentiation is common, and associated reactive lymphoid follicles are often present.

However, despite some shared features, they differ in etiopathogenesis, with further differences among EMZLs arising in different anatomic sites.^[15]

The T/NK cell neoplasms although are of many types; here, we discuss peripheral T-cell lymphoma, not otherwise specified (NOS), angioimmunoblastic T-cell lymphoma, anaplastic large cell lymphoma (ALCL), and extranodal NK/T-cell lymphoma (ENKTL) [Table 3]. These tumors are positive for pan T-cell markers except for ALCL which may demonstrate CD3 negativity, although ALCL demonstrates CD4 positivity as they are follicular T-cell lymphomas. A common family terminology of nodal T-follicular helper cell lymphomas (NTFHLs) is introduced in WHO-HAEM5, with previously recognized diseases now regarded as entities within this family. Accordingly, diseases previously referred to as “angioimmunoblastic T-cell lymphoma,” “follicular T-cell lymphoma,” and “peripheral T-cell lymphoma with TFH phenotype” are renamed NTFHL angioimmunoblastic-type, NTFHL follicular-type, and NTFHL-NOS, respectively.^[9] This is due to recognition of their significant clinical and immunophenotype overlapping as well as similar T follicular helper cell (TFH) gene expression signature and mutation profiles.^[16,17] ENKTL nasal-type has been renamed to ENKTL and the suffix “nasal type” has been dropped in WHO-HAEM5 as there is recognized presentation of this disease at various extranodal sites.^[9] Recently, a treatment against CD30 has been introduced and is often performed on various T-cell lymphomas.^[18]

T-lymphoblastic lymphoma/leukemia (T-LBL) and B-lymphoblastic lymphoma/leukemia (B-LBL) are morphologically indistinct on routine histology. In such cases, a terminal deoxynucleotidyl transferase and CD99 establish a precursor lesion and further differentiation into T- and B-cell can be established by CD3 and CD20. T-LBL expresses CD3 positivity while B-LBL is CD3 and CD20 negative. Possibility of a B-cell lineage can be demonstrated further by CD79a, PAX, or CD19. In the latest WHO classification, T-LBL and B-LBL have been renamed as T-LBL NOS and B-LBL not further classified (Whenever, genetic testing is not used to classify it otherwise).^[9] Outside the specific lineage lymphomas, tumors with expression of features of both CHL and DLBCL were termed as GZLs. Although the disease when first described was thought to be primarily mediastinal in presentation, now it is clear that it can be both mediastinal and disseminated presentation with or without mediastinal involvement. While the former is termed Mediastinal GZLs, characterized by younger age, early stage, the presence of a bulky tumor, and the latter termed as non-mediastinal GZLs tends to appear at an older age with bone marrow, and extranodal organ involvement.^[19] Recent literature reports suggest that the non-mediastinal B-cell lymphomas are more common than the mediastinal lymphomas.^[20] However, in the recent WHO classification, GZLs outside mediastinum are thought to have different genetic alterations and they are to be considered as DLBCL NOS.^[9]

CONCLUSION

Immunohistochemistry serves a major role in the diagnosis of lymphoma, especially in identifying the following characteristics: Cell lineage, maturation phase, cell proliferation, specific genetic alterations, and various therapeutic targets. However, recent WHO classification recognizes the significance of genetic and molecular data in the evaluation of a lymphoid neoplasm. Where it ascertains a neoplasm into a category, family/class, entity/type, and subtype, this has been formulated in such a manner that it is possible in settings globally; however, consideration is given to the fact that these resources are not universally available. In resource limited settings, a strict morphological and IHC-based categorization helps in reaching at an appropriate diagnosis.