Marginal zone B-cell lymphomas: an appraisal

Classification of canine malignant lymphomas according to the World Health Organization criteria

A study was carried out to test the accuracy and consistency of veterinary pathologists, not specialists in hematopathology, in applying the World Health Organization (WHO) system of classification of canine lymphomas. This study represents an initiative of the ACVP Oncology Committee, and the classification has been endorsed by the World Small Animal Veterinary Association (WASVA). Tissue biopsies from cases of canine lymphoma were received from veterinary oncologists, and a study by pathologists given only signalment was carried out on 300 cases. Twenty pathologists reviewed these 300 cases with each required to choose a diagnosis from a list of 43 B and T cell lymphomas. Three of the 20 were hematopathologists who determined the consensus diagnosis for each case. The 17 who formed the test group were experienced but not specialists in hematopathology, and most were diplomates of the American or European Colleges of Veterinary Pathology. The overall accuracy of the 17 pathologists on the 300 cases was 83%. When the analysis was limited to the 6 most common diagnoses, containing 80% of all cases, accuracy rose to 87%. In a test of reproducibility enabled by reintroducing 5% of cases entered under a different identity, the overall agreement between the first and second diagnosis ranged from 40 to 87%. The statistical review included 43,000 data points for each of the 20 pathologists.

Malignant and benign lymphoid lesions of the lung

Lymphoid lesions of the lung produce a complex of problems for the practicing pathologist. Although these lesions are eventually referred to hematopathologists, it is still the general surgical pathologist who first encounters them and confronts the problem of formulating an initial diagnosis. Over the last 20 years there has been a revolution in our knowledge of the classification and natural history of the pulmonary lesions, a plethora of information which warrants a thorough review. The purpose of this discussion is to report the clinical features and courses, pathologic features and, when known, etiologies or pathogenesis of the major "primary" pulmonary lymphoid lesions and present a brief approach to differential diagnosis. I will divide the lesions into malignant and benign, discussing each in turn.

Is lymphoplasmacytic lymphoma/immunocytoma a distinct entity? A clinicopathologic study of 20 cases

Lymphoplasmacytic lymphoma/immunocytoma (LLI) was defined initially as a small B-cell lymphoma with plasmacytoid or plasmacytic features. Because other types of small B-cell lymphoma, particularly marginal zone B-cell lymphoma may exhibit plasmacytic differentiation, the revised European-American lymphoma classification and World Health Organization has defined LLI more narrowly to exclude other small B-cell lymphomas. The goal of this study was to reevaluate LLI as a clinicopathologic entity. Twenty cases were selected from 43 previously diagnosed as "small lymphocytic lymphoma, plasmacytoid" or "immunocytoma" from 1985 to 1998. Cases fulfilling the criteria for B-cell small lymphocytic lymphoma, follicular lymphoma, marginal zone B-cell lymphoma, or other types of B-cell lymphoma were excluded. The histopathology and immunoreactivity for CD20, CD79a, CD3, CD43, CD23, CD5, kappa, lambda, and immunoglobulins (Ig's) M, G, and A were reviewed, in addition to available clinical findings. There were 13 men and seven women, with a mean age of 69 years. Five patients had documented Waldenström's macroglobulinemia (WM). Three architectural patterns were observed. Pattern A (seven of 20) showed open sinuses, small follicles, and hemosiderosis; pattern B (four of 20) showed hyperplastic follicles; and pattern C (nine of 20) showed diffuse effacement. Epithelioid histiocytes were prominent in patterns B and C but absent in A. Cytologically, six of 20 were polymorphous with 10% to 40% transformed cells; 14 of 20 were lymphoplasmacytic. Five cases showed minor foci of monocytoid B cells. One case showed a composite histology of LLI and small lymphocytic lymphoma. Amyloid was present in two cases. All cases were CD20 and/or CD79a immunoreactive, with two of 20 positive for CD43. Twelve cases were kappa monoclonal and eight cases were lambda monoclonal. Twelve of 17 cases that could be evaluated were positive for IgM and five were positive for IgG. All cases were negative for CD5 and CD23 with the exception of the one case with a composite histology. Eleven of 20 patients with available follow-up died of disease (median, 48 months), and eight of 20 are alive with disease at a follow-up of 6 months to 2 years. LLI does appear to represent a distinct clinicopathologic entity even though it shows morphologic heterogeneity and overlapping features with marginal zone B-cell lymphoma and small lymphocytic lymphoma. Recognition of LLI is important because the overall prognosis may be worse than for other types of small B-cell lymphomas.

Comparison of lymphoid neoplasm classification. A blinded study between a community and an academic setting

The revised European-American classification of lymphoid neoplasms has been reported as reproducible among expert pathologists and feasible in a community setting. We evaluated the reproducibility of lymphoid neoplasm diagnoses between a community and an academic center. We subtyped 188 lymphoid neoplasms using revised European-American classification criteria. Clinical findings, histologic or cytologic preparations, paraffin-section immunostains, and flow cytometry data were reviewed as appropriate. Diagnoses were compared only after completion of the study. Lymphoma subtype was concordant for 167 (88.8%) of 188 cases. Discordant cases included 15 B-cell, 2 T-cell, and 4 Hodgkin lymphomas. For B-cell neoplasms, discordance was most often due to classifying diffuse large cell lymphoma as another aggressive subtype of lymphoma (n = 6), marginal zone lymphoma as another subtype (n = 4), or follicle center lymphoma grade II as grade III (n = 3). For Hodgkin disease, discordance was most often due to classifying nodular sclerosis as mixed cellularity type (n = 3). Comparison of community and academic center diagnoses demonstrated high concordance for most revised European-American classification subtypes. Some sources of discordance have been addressed in the new World Health Organization classification of neoplastic diseases of the hematopoietic and lymphoid tissues.

Lymphomas with follicular and monocytoid B-cell components. Evidence for a common clonal origin from follicle center cells

We investigated the clonal relationship between follicular center cell and monocytoid B-cell components of non-Hodgkin lymphoma by isolating the components and comparing the nucleotide sequences of the complementarity-determining region (CDR)3 of the rearranged immunoglobulin heavy chain (IgH) gene. Paraffin blocks from 4 cases with amplifiable DNA using the polymerase chain reaction (PCR) were identified. Multiple representative cell clusters of the 2 components were obtained by microdissection, and the IgH CDR3 was amplified using a seminested PCR. Most of the PCR products obtained from both tumor components in each case had identical lengths when analyzed with polyacrylamide gel electrophoresis (PAGE) and identical migratory patterns on denaturing gradient gel electrophoresis (DGGE). These findings indicate sequence identity of the IgH CDR3 of both tumor components. Sequence analysis showed that point mutations were responsible for bands from the same case that had nonidentical migratory patterns by DGGE. The components in each of the 4 cases studied have the same clonal origin. Intraclonal sequence variations in the IgH gene were observed in 2 cases, consistent with the presence of continued somatic hypermutation after establishment of the clone. The expression of CD10 and bcl-2, as well as the detection of bcl-2 rearrangements in 2 cases, indicate that these lymphomas are of follicular center cell origin.

Follicular lymphoma with monocytoid B-cell proliferation: molecular assessment of the clonal relationship between the follicular and monocytoid B-cell components

Although a number of studies have recognized that follicular lymphomas may be accompanied by a prominent proliferation of monocytoid B-cells, the clonal relationship between these components has not been adequately assessed. Using laser capture microdissection, we isolated the follicular and monocytoid B-cell components from four well-characterized cases of follicular lymphoma with prominent monocytoid B-cells. DNA from each component was analyzed using polymerase chain reaction (PCR)-based methods to assess for clonal rearrangements of the immunoglobulin heavy chain gene (IgH) and for the presence of the bcl-2 gene major breakpoint region/joining region (MBR/JH) DNA fusion products by conventional PCR and fluorescence melting curve analysis. Evidence of clonal identity was established in the follicular and monocytoid B-cell components of three cases by demonstration of IgH gene rearrangements of identical size using IgH PCR, by comparison of complementarity determining region III (CDRIII) DNA sequences, or by detection of bcl-2 MBR/JH fusion products of identical size and/or melting temperature. Molecular analysis of the fourth case revealed a monoclonal and MBR/JH-positive follicular component accompanied by a polyclonal and MBR/JH-negative monocytoid B-cell proliferation. We conclude that the follicular and monocytoid B-cell components of this variant of follicular lymphoma are clonally identical in the majority of cases. However, in a minority of these cases, the monocytoid B-cell component is reactive. Larger studies that assess the prognostic significance of follicular lymphoma with monocytoid B-cells will benefit from molecular studies that assess the clonal relationship of both components.

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.

Fine-needle aspiration biopsy findings in marginal zone B cell lymphoma

Marginal zone B cell lymphomas (MZBCLs) represent a category of non-Hodgkin's lymphoma which may arise in a wide variety of extranodal organs where they are termed low grade B cell lymphomas of mucosa-associated lymphoid tissue (MALT). MZBCLs may involve primarily lymph nodes and or spleen where they are designated monocytoid B cell lymphoma or splenic marginal zone lymphoma, respectively. Recognition of this category of lymphoma, in particular, extranodal MALT lymphoma, is clinically significant in determining optimal therapy. Although there have been recent case reports describing the cytologic findings in low grade MALT lymphoma in various extranodal organs, this category of lymphoma has not been widely recognized or discussed in the cytology literature. The cytologic findings in seven fine-needle aspirations and two bronchial washings of histologically confirmed marginal zone lymphoma (five extranodal MALT lymphomas and four nodal marginal zone lymphomas) are described. In all of the cases, the cytologic specimens showed a polymorphous proliferation comprising a predominant population of intermediate sized lymphoid cells with centrocyte-like or monocytoid features, transformed cells, and variable numbers of plasma cells. These findings, while highly suggestive of MALT lymphoma in extranodal proliferations, may be more difficult to distinguish from reactive conditions in lymph nodes.

A Clinical Evaluation of the International Lymphoma Study Group Classification of Non-Hodgkin's Lymphoma

The recognition of several new types of non-Hodgkin's lymphoma (NHL) in recent years has led to proposals for changing lymphoma classifications, including a new proposal put forth by the International Lymphoma Study Group (ILSG). However, the clinical significance of the new entities and the practical utility of this new proposal have not been studied. Therefore, we performed a clinical evaluation of the ILSG classification. A cohort of 1,403 cases of NHL was organized at nine study sites around the world and consisted of consecutive patients seen between 1988 and 1990 who were previously untreated. A detailed protocol for histologic and clinical analysis was followed at each site, and immunologic characterization as to T- or B-cell phenotype was required. Five expert hematopathologists visited the sites and each classified each case using the ILSG classification. A consensus diagnosis was also reached in each case, and each expert rereviewed a 20% random sample of the cases. Clinical correlations and survival analyses were then performed. A diagnosis of NHL was confirmed in 1,378 (98.2%) of the cases. The most common lymphoma types were diffuse large B-cell lymphoma (31%) and follicular lymphoma (22%), whereas the new entities comprised 21% of the cases. Diagnostic accuracy was at least 85% for most of the major lymphoma types, and reproducibility of the diagnosis was 85%. Immunophenotyping improved the diagnostic accuracy by 10% to 45% for a number of the major types. The clinical features of the new entities were distinctive. Both the histologic types and the patient characteristics as defined by the International Prognostic Index predicted for patient survival. In conclusion we found that the ILSG classification can be readily applied and identifies clinically distinctive types of NHL. However, for clinical application, prognostic factors as defined by the International Prognostic Index must be combined with the histologic diagnosis for appropriate clinical decisions.