Plasmacytic differentiation in follicular center cell (FCC) lymphomas

Histopathologic, immunophenotypic, and mutational landscape of follicular lymphomas with plasmacytic differentiation

Follicular lymphomas with plasmacytic differentiation (FL-PCD) include two major subtypes: one with predominantly interfollicular PCD that usually harbors a BCL2 rearrangement (BCL2-R), and a second that has predominantly intrafollicular PCD and the frequent absence of a BCL2-R. It is proposed that these latter cases share some features with marginal zone lymphomas (MZL). To further explore this hypothesis in an expanded cohort of FL-PCD, a clinicopathologic investigation of 25 such cases was undertaken including an analysis of their mutational landscape. The 10 interfollicular FL-PCDs exhibited typical intrafollicular centrocytes/centroblasts (90%), CD10 expression (90%), full PCD including expression of CD138 by the plasma cells (PC) (100%), and PCs with class-switched immunoglobulin heavy chains (70%). These cases were BCL2-R positive (100%), BCL6-R positive in 30%, lacked extra BCL2 copies, and only 22% had extra copies of BCL6. Similar to classic FLs, 80% of interfollicular FL-PCDs harbored mutations in epigenetic regulators KMT2D (70%), CREBBP (40%), and/or EZH2 (30%). In contrast, only 45% of 11 intrafollicular FL-PCDs demonstrated typical intrafollicular centrocytes/centroblasts, 55% were CD10(-), 80% contained IgM+ PCs, and only 27% harbored BCL2-Rs. BCL6-Rs were identified in 27% of intrafollicular FL-PCD, while 60% showed extra copies of BCL2 and 50% extra copies of BCL6, consistent with complete or partial trisomies of chromosomes 18 and 3, respectively. Only 54% of intrafollicular FL-PCDs showed mutations in epigenetic regulators. Both subtypes showed mutational differences compared to classic FL, but only the interfollicular subtype showed differences from what is reported for nodal MZL. Four additional cases showed mixed intra- and interfollicular PCD. These results suggest that FL-PCD has some distinctive features and supports the existence of two major subtypes. The interfollicular PCD subtype shares many features with classic FL. The intrafollicular FL-PCDs are more heterogeneous, have differences from classic FL, and have a greater morphologic, immunophenotypic, and genetic overlap with MZL.

Primary cutaneous follicle center lymphoma with extensive plasmacytic differentiation and t(14;18) in both the lymphoid and plasma cell components

Primary cutaneous follicle center lymphoma (PCFCL) is the most common cutaneous B-cell lymphoma. The typical immunophenotype includes expression of both CD20 and BCL6, with the majority of cases lacking expression of CD10, BCL2, and the characteristic t(14;18)/IGH-BCL2 rearrangement seen in systemic follicular lymphoma (FL). Plasmacytic differentiation (PD) is an uncommon finding in both systemic and cutaneous FLs and presents a diagnostic challenge when present, leading to the potential for misdiagnosis as marginal zone lymphoma (MZL). Limited reports have described light chain restriction in the plasma cell component of FLs with PD, and rare cases of PCFCL with PD have been described. While the IGH-BCL2 translocation has been identified in a subset of FLs with PD, the presence of the BCL2 translocation in monotypic plasma cells of PCFCL has not been previously described to our knowledge. Here, we report a case of PCFCL with extensive PD in a 77-year-old woman that was favored to represent primary cutaneous MZL on an initial punch biopsy. Excisional biopsy, however, revealed that the atypical lymphocytes expressed CD10, BCL6, and BCL2, while the plasma cell component demonstrated light-chain lambda restriction. FISH studies showed the presence of an IGH-BCL2 translocation in both the lymphocytic and plasmacytic components.

Cutaneous follicle center lymphomas with plasmacytic differentiation

Follicle center lymphomas, including primary cutaneous follicle center lymphoma (PCFCL), may rarely show plasmacytic differentiation. Such cases can pose a diagnostic challenge and can be mistaken for other lymphomas that more commonly include plasma cells. Here, we report four cases of PCFCL and one case of systemic follicular lymphoma involving the skin with associated monotypic plasma cells, including the clinical, morphologic and immunophenotypic features.

The broad landscape of follicular lymphoma: Part I

Follicular lymphoma is a neoplasm derived from follicle center B cells, typically both centrocytes and centroblasts, in variable proportions according to the lymphoma grading. The pattern of growth may be entirely follicular, follicular and diffuse, and rarely completely diffuse. It represents the second most common non-Hodgkin lymphoma, after diffuse large B-cell lymphoma and is the most common low-grade mature B-cell lymphoma in western countries. In the majority of cases, follicular lymphoma is a nodal tumor, occurring in adults and frequently associated with the translocation t(14;18)(q32;q21)/IGH-BCL2. However, in recent years the spectrum of follicular lymphoma has expanded and small subsets of follicular lymphoma, which differ from common follicular lymphoma, have been identified and included in the current 2017 WHO classification. The aim of our review is to describe the broad spectrum of follicular lymphoma, pointing out that the identification of distinct clinicopathological variants of follicular lymphoma is relevant for patient outcomes and choice of treatment.

Molecular characteristics of mantle cell lymphoma presenting with clonal plasma cell component

The normal counterparts of mantle cell lymphoma (MCL) are naive, quiescent B cells that have not been processed through the germinal center (GC). For this reason, although lymphomas arising from GC or post-GC B cells often exhibit plasmacytic differentiation, MCL rarely presents with plasmacytic features. Seven cases of MCL with a monotypic plasma cell (PC) population were collected from 6 centers and were studied by immunohistochemistry, fluorescence immunophenotyping and interphase cytogenetics as a tool for the investigation of neoplasms analysis, capillary gel electrophoresis, and restriction fragment length polymorphism of immunoglobulin heavy chain analysis of microdissections of each of the MCL and PC populations to assess their clonal relationship. The clinical presentation was rather unusual compared with typical MCL, with 2 cases arising from the extranodal soft tissues of the head. All MCL cases were morphologically and immunohistochemically typical, bearing the t(11;14)(q13;q32). In all cases, the PC population was clonal. In 5 of the 7 cases, the MCL and PC clones showed identical restriction fragments, indicating a common clonal origin of the neoplastic population. The 2 cases with clonal diversity denoted the coexistence of 2 different tumors in a composite lymphoma/PC neoplasm. Our findings suggest that MCL can present with a PC component that is often clonally related to the lymphoma, representing a rare but unique biological variant of this tumor.

Recent Advances in Follicular Lymphoma: Pediatric, Extranodal, and Follicular Lymphoma in Situ

Follicular lymphoma is a relatively common B-cell lymphoma composed of follicle center B lymphocytes. Follicular lymphomas occurring in the pediatric population and in some extranodal sites exhibit particular clinicopathologic features and clinical behavior that are often distinct from adult nodal follicular lymphoma. A type of "in-situ" follicular lymphoma presents as intrafollicular neoplastic cells in a background of architecturally normal lymphoid tissue and may be difficult to recognize in routine sections. Accurate recognition of the morphologic variants and clinicopathologic subtypes of follicular lymphoma is important to avoid confusing them with other lymphomas and reactive processes; in addition, some of these subtypes of follicular lymphoma display unusually indolent clinical behavior that warrant their separation from "conventional" follicular lymphoma.

Follicular lymphomas with plasmacytic differentiation include two subtypes

Follicular lymphomas with plasmacytic differentiation were described more than two decades ago. However, the possibility that some of these reported cases are marginal zone lymphomas or composite lymphomas must be considered. In addition, it is also uncertain whether follicular lymphomas with plasmacytic differentiation have any unique cytogenetic or other features. Therefore, fluorescence immunophenotypic and interphase cytogenetic analysis of 14 well-characterized follicular lymphomas with plasmacytic differentiation was performed using a CD138 antibody to identify the plasma cells and with BCL2, BCL6, IGH@ and MALT1 break-apart probes and a chromosome 12 centromeric probe. CD10 was expressed in 12/14 cases, BCL6 in 12/12 cases and BCL2 in 12/14 cases. At least one cytogenetic abnormality was identified in 12/14 cases. The same abnormality was present in both the plasmacytic (CD138+) and non-plasmacytic (CD138-) component in all 10 evaluable cases. BCL2 rearrangements were present in seven cases (5 IGH@ rearranged, 1 IGH@-not rearranged, 1 IGH@-not evaluable), BCL6 rearrangement in two (1 also with BCL2/IGH@ rearrangement), +12 in 1, +MALT1 without +18 in 1, IGH@ rearrangement without other abnormalities in 1 and IGH@ rearranged or partially deleted in 1 case. No cases showed +BCL6 (3q27) or a MALT1 rearrangement. All six cases with an isolated BCL2 rearrangement had predominantly interfollicular plasmacytic cells whereas, 6/7 cases without the translocation had concentrations of intrafollicular or perifollicular plasmacytic cells (P<0.005), as did the case with BCL2 and BCL6 translocations. These results support the existence of bona fide follicular lymphomas with plasmacytic differentiation and support the clonal relationship of the neoplastic lymphoid and plasma cells in at least most of these cases. The differential distribution of the plasma cells, specifically in relation to the presence or absence of an isolated BCL2 rearrangement suggests that the latter cases may be distinctive, sharing some features with marginal zone lymphomas.

Indolent lymphomas of mature B lymphocytes

The lymphomas of small B lymphocytes are a biologically diverse group of B cell derived neoplasms that includes B cell small lymphocytic lymphoma/chronic lymphocytic leukemia; mantle cell lymphoma; follicular lymphoma; nodal, splenic and extranodal marginal zone lymphomas; and lymphoplasmacytic lymphoma. They are distinguished from one another on clinical, morphological, phenotypic and genetic grounds. This article reviews the essential diagnostic and biologic features of these clinically indolent B cell malignancies.

Histological and immunophenotypic changes in 59 cases of B-cell non-Hodgkin's lymphoma after rituximab therapy

Rituximab is a chimeric monoclonal antibody that recognizes the CD20 antigen. It has been used to treat B-cell non-Hodgkin lymphoma (B-NHL), but recently rituximab resistance has been a cause for concern. We examined histological and immunohistochemical changes in 59 patients with B-NHL after rituximab therapy. The patients comprised 32 men and 27 women with a median age of 59 years. Pre-rituximab specimens comprised 34 follicular lymphomas (FL), 11 diffuse large B-cell lymphomas (DLBCL), 10 mantle cell lymphomas, two marginal zone B-cell lymphomas (MZBCL), and two chronic lymphocytic leukemias (CLL). CD20 expression in lymphoma cells was evaluated by immunohistochemistry or flow cytometry. Post-rituximab materials were taken a median of 6 months (4 days to 59 months) after rituximab therapy. Sixteen cases (27%) showed loss of CD20 expression with four histological patterns: pattern 1, no remarkable histological change (FL, 5; DLBCL, 3; and CLL, 2); pattern 2, proliferation of plasmacytoid cells (FL, 2; DLBCL, 1; and MZBCL, 1); pattern 3, transformation to classical Hodgkin's lymphoma (FL, 1); and pattern 4, transformation to anaplastic large cell lymphoma-like undifferentiated lymphoma (FL, 1). Loss of CD20 was unrelated to the interval of biopsies, treatment regimen, clinical response, and frequency of rituximab administration. Loss of CD20 within 1 month of rituximab therapy (3/14, 21%) and regain of CD20 (2/7, 29%) were not frequent. CD20-positive relapse with transformation occurred most frequently in cases of early relapse. In conclusion, B-NHL showed various histological and immunophenotypic changes after rituximab therapy, including not only CD20 loss but also proliferation of plasmacytoid cells or transformation to special subtypes of lymphoma.

Application of Immunohistochemistry in the Diagnosis of Non-Hodgkin and Hodgkin Lymphoma

Context.—Beginning with the immunologic classifications of Lukes and Collins and Kiel and culminating in the Revised European-American Lymphoma and World Health Organization classifications, the diagnosis of lymphoid tumors relies heavily on the determination of cell lineage, maturation, and function, based on antigen expression in addition to morphology and clinical features. Technologic advances in immunology, antibody production, genetic analysis, cloning, and the identification of new genes and proteins by microarray and proteomics have provided pathologists with many antibodies to use in routine diagnosis.

Objective.—To provide guidance to the practicing pathologist in the appropriate selection of an antibody panel for the diagnosis of lymphoma based on morphology and relevant clinical data and to avoid pitfalls in the interpretation of immunohistochemical data. Attention is given to some of the newer antibodies, particularly against transcription factors, that are diagnostically and prognostically useful.

Data Sources.—The information presented in this article is based on review of the literature using the OVID database (Ovid MEDLINE 1950 to present with daily update) and 20 years of experience in diagnostic hematopathology.

Conclusions.—Immunophenotyping is required for the diagnosis and classification of lymphoid malignancies. Many paraffin-reactive antibodies are available to the pathologist but most are not specific. To avoid diagnostic pitfalls, interpretation of marker studies must be based on a panel and knowledge of a particular antigen's expression in normal, reactive, and neoplastic conditions.

Mantle cell lymphoma with plasma cell differentiation

The differentiation of B lymphocytes into plasma cells (PCs) is an antigen-mediated process that largely depends on the interaction between B cells and regulatory factors in their microenvironment. Long-lived PCs are derived from activated B cells in the germinal center (GC), whereas PC differentiation from naive B cells occurs in the extrafollicular areas and the PCs are short-lived. Consequently, lymphomas arising from post-GC B cells often exhibit plasmacytic differentiation, whereas lymphomas arising from naive B cells less commonly show plasmacytic differentiation. Herein, we report 2 cases of mantle cell lymphoma (MCL) with clonal PC differentiation. Both cases presented with the typical cytologic features of MCL and were characterized by a nodular and mantle-zone growth pattern. Clusters of clonal PCs with monotypic kappa light chain expression were identified in the centers of the tumor nodules and within reactive GCs. FICTION (Fluorescence immunophenotyping and Interphase Cytogenetics as a Tool for the Investigation Of Neoplasms) analysis demonstrated the characteristic t(11;14)(q13;q32) in both the MCL cells and clonal PCs, indicating that both cell types were derived from the same B-cell clone. These findings indicate that the clonal PC differentiation may occur within GCs in some cases of MCL.

Centrocytoid Plasma Cells of the Germinal Center

Germinal centers within the lymph node follicles are T-cell-dependent, antigen-driven B-cell proliferations that develop from the rapid clonal expansion of a few founder cells. The end results of this B-cell expansion are memory B cells or plasma cells. Two morphologic forms of plasma cell can be recognized in the germinal center: classic plasma cells, characterized morphologically by peripherally clumped arrangement of nuclear chromatin, and cells with a nuclear morphology more resembling that of the centrocytes, which the authors have termed "centrocytoid plasma cells." In this study the authors examined the distribution and immunohistochemical characteristics of these two populations of germinal center plasma cells. The centrocytoid plasma cells were arranged in a band stretching from the junction of the dark and light zone to the periphery of the germinal centers, while the classic plasma cells were mainly present at the germinal center periphery. Both marked with CD38, CD138, and VS38c, recognized markers for plasma cells; however, EMA and CD31 were present only in the classic form of plasma cell. The proliferation marker Ki67 was present in less than 1% of the cells labeling with CD138. Others have demonstrated Ki67 in 50% of the cells labeled with Blimp-1, which is consistent with Blimp-1 appearing earlier than CD138 in ontogeny. CD10 is co-expressed with CD138 in about 10% of cells and CD45 with CD138 in about 5% of cells. Their topographic features, together with the progressive acquisition of plasma cell markers, suggest that the centrocytoid plasma cells may be the precursors of the classic plasma cells. Of note, both the forms of plasma cell were absent in follicles of follicular lymphoma, which supports the concept that in this disease, lymphocytes fail to differentiate and mature beyond the centrocyte stage.

Despite apparent morphologic and immunophenotypic heterogeneity, Waldenstrom's macroglobulinemia is consistently composed of cells along a morphologic continuum of small lymphocytes, plasmacytoid lymphocytes, and plasma cells

We studied the clinical, morphologic, and immunophenotypic features of 26 Waldenstrom's macroglobulinemia (WM) cases, each with an IgM spike of >or=3.0 g/dL. The neoplastic cells were consistently composed of a spectrum of small lymphocytes, plasmacytoid lymphocytes, and plasma cells. Bone marrow (BM) involvement ranged from 10% to 90%, showed four histologic patterns (nodular [75%], interstitial [75%], paratrabecular [42%], and diffuse [4%]), two histologic subtypes (lymphoplasmacytic [87%] and lymphoplasmacytoid [13%]), and several cytologic variants (monocytoid [n = 2], signet-ring cell [n = 2], and hairy cell leukemia-like [n = 1]). By flow cytometry (FC), all cases expressed monoclonal surface immunoglobulin, CD19, and CD20. Most cases (58%) lacked expression of CD5, CD10, and CD23. However, variants such as CD5(+)CD10(-)CD23(-) (n = 3), CD5(+)CD10(-)CD23(+) (n = 1), and CD5(-)CD10(+)CD23(+/-) (n = 2) were seen. At last follow-up, 18 of 26 patients were alive (median survival, 94 months). Causes of death included WM (n = 1), large cell lymphoma (n = 1), acute myeloid leukemia (likely therapy-related [n =2]), and nonhematologic/unknown. When individual WM cases are compared, apparent morphologic diversity is suggested. However, every WM case is comprised of cells along a morphologic continuum from small lymphocytes to plasma cells, delineating a uniform, consistent pathology. As WM shows immunophenotypic heterogeneity, morphology must be the cornerstone of the diagnosis.

Utility of flow cytometry in subtyping composite and sequential lymphoma

Composite lymphoma (CL) is defined as more than one distinct lymphoma variant occurring in the same anatomic site, and sequential lymphoma (SL) is defined as different lymphoma variants occurring at different sites or at different times in the same patient. The utility of flow cytometry immunophenotyping in evaluating CL and SL has only been investigated in a few single-case studies. To further define the utility of flow cytometry in evaluating these tumors, records were searched at two institutions. Cases representing high-grade progression of low-grade lymphoma were excluded. For each CL/SL, clinical data was obtained and morphology was evaluated in routinely processed H&E-stained tissue sections. Tumor components were subtyped using revised European-American classification (REAL) criteria. Follicle center components were graded using modified Rappaport criteria. Immunophenotype was determined using two-color flow cytometry and paraffin-section immunostains. Four cases were identified. Case 1, nodal follicle center, follicular, grade III plus marginal zone CL, showed two discrete populations of monoclonal B-cells that differed in their expression of CD10. Case 2, cutaneous lymphoplasmacytoid lymphoma followed by mesenteric non-Hodgkin's lymphoma (lymphoplasmacytoid plus follicle center, follicular, grade III) plus Hodgkin's disease CL, showed CD5-/CD10-/CD19+/kappa+ cells by flow cytometry in both tissue samples. The Hodgkin's disease component showed CD3-/CD15-/CD20-/CD30+ Reed-Sternberg cell variants in paraffin-section immunostains. Case 3 represented nodal follicle center lymphoma, follicular, grade I (CD3-/CD5-/CD10-/CD19+/kappa+) followed by cutaneous anaplastic large T-cell lymphoma (CD2+/CD4+/CD5+/CD19- cells with partial expression of CD3 and CD7). Case 4 represented cutaneous follicle center lymphoma, follicular, grade I (CD5-/CD10+/CD19+/CD23+/lambda+) followed by bone marrow B-cell small lymphocytic lymphoma (CD5+/CD10-/CD19+/CD23+/kappa+). Results show that flow cytometry is a potentially useful adjunct in characterizing CL and SL.

Marginal zone B-cell lymphomas: an appraisal

Although the Revised European-American Lymphoma Classification does not utilize the term monocytoid B-cell Lymphoma, there are numerous reasons to support its use in classifying lymphomas of so-called marginal zone B-cell type that contain a distinct population of malignant monocytoid B-cells. In addition, there are other B-cell lymphomas which have very distinctive morphological features, because they show multiple and very well demarcated histologies characterized by presence of cells that appear to be (1) malignant monocytoid B-cells and malignant follicular center cells, or (2) malignant monocytoid B-cells, malignant follicular center cells and malignant plasma cells, or (3) malignant monocytoid B-cells and malignant mantle cells. The neoplastic cells in each of the above three examples show identical light chain restriction and thus they are part of the same neoplastic clone. We believe that there are different types of precursor B-cells (memory or otherwise) for the above cells, and an arrest in differentiation of these precursor B-cells may readily explain the presence of these different morphological combinations. Recognition of these morphological types may lead to further awareness of the possibilities of the existence of multiple, linked pathways of differentiation for lymphoid cells including the possibility of different types of precursor B-cells. Furthermore, an understanding of the uniqueness of monocytoid B-cells would allow pathologists to use terminology that is less redundant and more precise.

Spontaneous follicular center cell lymphomas of B cell origin in cataract mice

Spontaneous lymphomas from a strain of hereditary cataract (CAC-nct/+) mice were examined by light and electron microscopy and by immunohistochemical reaction for the mouse heavy and light immunoglobulin chains. Lymphomas occurred in 28 out of 45 male cataract mice and in 34 out of 52 females at 25 to 65 weeks of age. All of the lymphoma-bearing mice showed an enlargement of the spleen and mesenteric lymph nodes, and some mice also had hepatomegaly. Morphologically, all tumors were composed of a mixed population of small and large cells. Neoplastic cells had features of follicular center cell lymphomas, such as scant to moderate amounts of cytoplasm and cleaved and/or round nuclei with a large nuclear-to-cytoplasmic ratio. Large cells were often admixed with small cells, and had vesicular nuclei with prominent nucleoli juxtaposed to the nuclear membrane. Intracytoplasmic eosinophilic inclusions were observed in occasional cells, but Golgi apparatus was poorly developed and rough-surfaced endoplasmic reticulum was scant, unlike those in plasma cells. C-particles were seen in all lymphoma-bearing mice by electron microscopy. Intracisternal A-particles were detected in some mice. Immunohistochemically, neoplastic lymphoid cells were positive for the kappa light chain and the surface/cytoplasmic immunoglobulin M. These results indicate that lymphoid cell neoplasms found in hereditary cataract mice originate from follicular center B cells.

Primary biphasic lymphoplasmacytic lymphoma of the lung. A mucosa-associated lymphoid tissue lymphoma with compartmentalization of plasma cells in the lung and lymph nodes

A primary mucosa-associated lymphoid tissue lymphoma of the lung in a 27-year-old man was found. The tumor was composed mainly of centrocyte-like cells and plasma cells. These two components were demarcated sharply from each other, resulting in a zoning or biphasic pattern. This characteristic pattern also was present in the involved regional lymph nodes. Monoclonality of tumor cells was shown immunohistochemically and by in situ hybridization techniques. This article also highlights the use of in situ hybridization in detecting light chain mRNA in paraffin sections.

Immunophenotypes of malignant lymphoma centroblastic-centrocytic and malignant lymphoma centrocytic: an immunohistologic study indicating a derivation from different stages of B cell differentiation

Five cases of intermediate lymphocytic lymphoma (ILL), 13 cases of malignant lymphoma centrocytic (MLCC), and 27 cases of malignant lymphoma centroblastic centrocytic (MLCBCC) were studied morphologically and with the aid of a panel of monoclonal antibodies. The immunophenotypes of ILL and MLCC (IgM+/IgD+, MT1+, CALLA-) indicate a mantle zone or very early follicle center derivation. The immunophenotypes of MLCBCC (IgM+ or IgG/IgA+, MT1-, CALLA+) indicate a "true" follicle center derivation. The morphologic diversity of MLCBCC could not be related to specific immunophenotypes.

Histological progression of follicular centre cell lymphomas to immunoglobulin-producing tumours in two pigs

Follicular centre cell lymphomas in two crossbred sows were examined histologically, immunologically and ultrastructurally. In one case, most of the involved tissues showed a diffuse growth pattern and follicular structures were present in some lymph nodes. In some areas, immunoblastoid cells were scattered or focal (immunoblastic transformation) and contained only cytoplasmic IgM (CIgM) or both CIgM and cytoplasmic IgG. In the other case, the neoplastic cells grew diffusely and an incompletely affected lymph node showed separate neoplastic follicles as well as direct transition into a diffuse growth pattern, without the stage of accumulated follicles. Scattered immunoblastoid or plasmacytoid cells with CIgM were present in some sections (plasmacytic differentiation). The origin and histological progression of these neoplasms are discussed and it is suggested that the presence of two immunoglobulins in single neoplastic cells could be the result of heavy chain class switch. As these swine lymphomas resembled human lymphomas they may offer useful models for the study of the latter.

Lymphoplasmacytoid lymphoma: an immunohistological study

Eighteen cases of lymphoplasmacytoid lymphoma (LPL) have been immunophenotypically characterized with a panel of 26 monoclonal antibodies. All cases expressed leucocyte common antigen, class II MHC and stained with B cell markers (CD19, CD20, CD22) although a variable proportion of tumour cells were noticed to have lost some B cell marker expression. There was some phenotypic heterogeneity with variable immunostaining with KB61, CD21, and CD5. A variable proportion of cells in all cases contained cytoplasmic immunoglobulin. Surface immunoglobulin light chain restriction was demonstrated in 11 cases and heavy chain predominance in 16 cases. Few tumour cells were proliferating as indicated by Ki67 immunostaining. A wide variation in number of macrophages and T lymphocytes were present in association with the tumours. A significant association between the expression of CD5 and the presence of peripheral blood lymphocytosis was noticed (p less than 0.003) but there was no association between CD5 and co-expression of IgM and IgD. This data supports an origin from non-germinal centre cells for LPL and suggests that CD5 expression by B cells may be related to lymphocyte migration. LPL shows some immunological heterogeneity and can present diagnostic difficulties, but its poor prognosis makes it an important category of lymphoma to recognise.

Neoplastic plasma cells in follicular lymphomas. Clinical and pathologic findings in six cases

Six cases of follicular lymphoma contained an abundant plasma cell component. With immunoperoxidase techniques, this was found to demonstrate monotypic cytoplasmic marking for either K or L Ig light chain in five cases, and for IgA heavy chain only in one case. A histogenetic relationship between follicular center cells and plasma cells was suggested by cell forms morphologically intermediate between these two types and by monotypic plasma cells in the neoplastic follicles. The progressive differentiation of follicular center cells into Ig-secreting cells in these cases is likely to be the result of an alteration of the immunoregulatory mechanisms that usually block the differentiation of follicular lymphomas. Four of our patients presented with disseminated disease, three had extranodal presentation and four manifested serum paraproteins. Their median survival was 40 months; two of them died of disease. The published data and our own suggest that follicular lymphoma with plasmacytic differentiation is a malignancy of intermediate grade, with survival and clinical features closer to lymphoplasmacytic/lymphoplasmacytoid lymphoma (LP immunocytoma) than to follicular lymphoma.