Leucemia linfocítica b em cão jovem: relato de caso / B - lymphocytic leukemia in young dog: case report / Leucemia linfocítica b en perro joven: relato de caso

O presente relato teve como objetivo descrever um caso de leucemia linfocítica B em um cão da raça maltês, fêmea, com três anos de idade, demonstrando a metodologia de diagnóstico e a variação da patologia clínica após o tratamento exclusivamente por esplenectomia. A linfocitose acentuada observada no hemograma e presença proliferativa de linfócitos na medula óssea determinou a suspeita da leucemia linfocítica. A leucemia linfocítica B foi diagnosticada por meio da citologia aspirativa da medula óssea, imunocitoquímica e citometria de fluxo. O tratamento foi exclusivamente por esplenectomia e dois anos após a cirurgia o animal não apresentou recidiva da afecção.

This report aimed to describe a case of B lymphocytic leukemia in maltese female dog, three years old, demonstrating the methodology of diagnostic and variation of clinical pathology after treatment exclusively by splenectomy. The accentuate lymphocytes observed in blood counts and presence of proliferative lymphocytes in the bone marrow were determined to diagnostic of lymphocytic leukemia. The B lymphocytic leukemia was diagnosed by bone marrow aspiration cytology, immunocytochemistry and flow cytometry. The treatment was exclusively by splenectomy and two years after the surgery the animal showed no recurrence of the disease.

El objetivo de ese relato ha sido describir un caso de leucemia linfocítica B en un perro, raza maltés, hembra, de tres años, demostrando la metodología de diagnóstico y la variación de la patología clínica, después del tratamiento exclusivamente por esplenectomía. La linfocitosis aguda, observada en el hemograma, y la presencia de proliferación de linfocitos en la médula ósea, determinó la sospecha de leucemia linfocítica. La leucemia linfocítica B fue diagnosticada mediante la citología por aspiración de médula ósea, inmunocitoquímica y citometría de flujo. El tratamiento fue exclusivamente por esplenectomía y dos años después de la cirugía el animal no mostró recurrencia de la enfermedad.

Differential expression of CD200 in B-cell neoplasms by flow cytometry can assist in diagnosis, subclassification, and bone marrow staging.

OBJECTIVES: To analyze CD200 expression by flow cytometry in a large series of B-cell neoplasms in a variety of tissue types in comparison with benign B-lineage cells. METHODS: We measured CD200 expression levels in 505 peripheral blood (PB), bone marrow (BM), and lymphoid tissue biopsy specimens, including 364 cases positive for B-cell leukemias and lymphomas. RESULTS: CD200 expression in chronic lymphocytic leukemia cases was as bright as or brighter than normal PB B cells in nearly all cases, while mantle cell lymphoma (MCL) cases were usually dim or negative. However, rare MCL cases (about 5%) were moderately bright for CD200. Marginal zone lymphomas varied by subtype, with nodal cases brighter, splenic cases dimmer, and extranodal cases heterogeneous for CD200 expression. Follicular lymphoma (FL) cells were brighter for CD200 in BM specimens than in lymph nodes. In some BM specimens, dim CD200 could distinguish FL cells from background hematogones. Large B-cell lymphomas of the non-germinal center type tended to be brighter for CD200 than those of the germinal center type, while Burkitt lymphomas were negative. CONCLUSIONS: CD200 staining by flow cytometry can be useful in the differential diagnosis of B-cell neoplasms and in their detection in the BM.

Mature B-cell lymphoma and leukemia in children and adolescents-review of standard chemotherapy regimen and perspectives.

Mature B-cell non-Hodgkin lymphoma (B-NHL) comprises more than 50% of all non-Hodgkin lymphoma (NHL) in children and adolescents. Many B-NHL subtypes frequently observed in adults are rarely diagnosed in children and adolescents. In this age group, Burkitt lymphoma (BL), Burkitt leukemia or FAB L3 leukemia (B-AL), diffuse large B-cell lymphoma (DLBCL), primary mediastinal large B-cell lymphoma (PMLBL), follicular lymphoma (FL), and aggressive mature B-NHL not further classifiable (B-NHL nfc) are the most common subtypes. Diverse clinical trials demonstrated similar results of current combination chemotherapy regimens succeeding in overall survival rates of more than 80%. However, treatment-related toxicity and the poor prognosis of relapse are serious concerns. Furthermore, specific histological B-NHL subtypes are rare in children and optimal treatment is not established. New treatment modalities are urgently needed for these patient groups. Rituximab, a monoclonal antibody that is already established in the treatment of adults with mature B-NHL, demonstrated promising results in pediatric patients. The definitive role of rituximab in the treatment of children and adolescents with B-NHL needs to be evaluated in prospective controlled clinical trials. This review provides a comprehensive overview of chemotherapy regimens and the perspectives for children and adolescents with mature B-cell lymphoma and leukemia.

Mixed-phenotype acute leukemia: historical overview and a new definition.

Acute leukemia with a mixed phenotype is a rare disease and comprises 2-5% of all acute leukemias. These disorders have been known historically by a variety of names, such as mixed lineage leukemia, bilineal leukemia and biphenotypic leukemia, and the criteria for diagnosis have often been arbitrary. The scoring criteria proposed by the European Group for the Immunological Characterization of Leukemias represented a major attempt to define this disorder. However, the relative weight given to some markers and the lack of lineage specificity of most markers have raised questions regarding the significance of this approach. In 2008, the World Health Organization classification of hematopoietic and lymphoid tumors proposed a simpler diagnostic algorithm, which relies on fewer and more lineage-specific markers to define mixed-phenotype acute leukemia (MPAL). MPAL with t(9;22) and MLL rearrangement have been separated. Several studies have suggested that patients with acute leukemia of mixed phenotype have a worse clinical outcome when compared with matched controls with acute myeloid leukemia or acute lymphoblastic leukemia. Further studies are needed to confirm the significance of MPAL as currently defined, to determine a standardized treatment approach and to better understand the biological and clinical aspects of this disease.

A comprehensive genetic and histopathologic analysis identifies two subgroups of B-cell malignancies carrying a t(14;19)(q32;q13) or variant BCL3-translocation.

The biologic and pathologic features of B-cell malignancies bearing a translocation t(14;19)(q32;q13) leading to a fusion of IGH and BCL3 are still poorly described. Herein we report the results of a comprehensive cytogenetic, fluorescence in situ hybridization (FISH), molecular and histopathological survey of a large series of B-cell malignancies with t(14;19) or variant translocations. A total of 56 B-cell malignancies with a FISH-proven BCL3 involvement were identified with the translocation partners being IGH (n=51), IGL (n=2), IGK (n=2) and a non-IG locus (n=1). Hierarchical clustering of chromosomal changes associated with the t(14;19) indicated the presence of two different groups of IG/BCL3-positive lymphatic neoplasias. The first group included 26 B-cell malignancies of various histologic subtypes containing a relatively high number of chromosomal changes and mostly mutated IgVH genes. This cluster displayed three cytogenetic branches, one with rearrangements in 7q, another with deletions in 17p and a third one with rearrangements in 1q and deletions in 6q and 13q. The second group included 19 cases, mostly diagnosed as B-cell chronic lymphocytic leukemia (B-CLL), and characterized by few additional chromosomal changes (e.g. trisomy 12) and unmutated IgVH genes. In conclusion, our study indicates that BCL3 translocations are not restricted to B-CLL but present in a heterogeneous group of B-cell malignancies.

The t(14;19)(q32;q13)-positive small B-cell leukaemia: a clinicopathologic and cytogenetic study of seven cases.

The t(14;19)(q32;q13), involving the BCL3 locus at chromosome 19q13 and the immunoglobulin heavy chain gene at 14q32, is a rare recurrent cytogenetic abnormality identified in B-cell neoplasms, most of which have been classified as chronic lymphocytic leukaemia (CLL) in the literature. We describe the clinicopathological, immunophenotypic and cytogenetic findings in seven patients with B-cell neoplasms associated with t(14;19)(q32;q13). There were five men and two women, with a median age of 48 years (range 33-68). All had absolute lymphocytosis, six had lymphadenopathy, and one had splenomegaly. Lymphocytes in blood and bone marrow aspirate smears were predominantly small and cytologically atypical. Flow cytometric immunophenotyping showed an atypical immunophenotype with low CLL scores. The growth pattern in bone marrow biopsy specimens was interstitial to diffuse; immunohistochemical stains were positive for bcl3 and negative for cyclin D1. Lymph node biopsy specimens of two patients revealed total architectural effacement by neoplasm with proliferation centres. In addition to t(14;19), cytogenetic studies demonstrated trisomy 12 in five patients. These results suggest that B-cell neoplasms with the t(14;19)(q32;q13) present frequently as leukaemia composed of small B-lymphocytes and share many features with CLL. However, these neoplasms also differ from CLL cytologically and in their immunophenotype.

Screening microarrays of novel monoclonal antibodies for binding to T-, B- and myeloid leukaemia cells.

We have developed a microarray (DotScan) that enables rapid immunophenotyping and classification of leukaemias and lymphomas by measuring the capture of cells by immobilized dots of 82 CD antibodies [Belov, L., de la Vega, O., dos Remedios, C.G., Mulligan, S.P., 2001. Immunophenotyping of leukemia using a cluster of differentiation antibody microarray. Cancer Res. 61, 4483; Belov, L., Huang, P., Barber, N., Mulligan, S.P., Christopherson, R.I., 2003. Identification of repertoires of surface antigens on leukemias using an antibody microarray. Proteomics 3, 2147]. The DotScan technology has been used to investigate the properties of 498 new antibodies submitted to the HLDA8 Workshop. These antibodies have been applied as 10 nl dots to a film of nitrocellulose on a microscope slide to make an HLDA8 microarray. After blocking the remaining nitrocellulose surface, individual arrays were incubated with each of 7 cell types from a human leukaemia cell panel consisting of three cell lines, CCRF-CEM (a T-cell acute lymphocytic leukaemia), MEC-1 (derived from B-cell chronic lymphocytic leukaemia) and HL-60 (a promyelocytic leukaemia), and four leukaemias from patients: a T-cell prolymphocytic leukaemia, a B-cell chronic lymphocytic leukaemia, and two acute myeloid leukaemias. Leukaemia cells were captured by those immobilized antibodies for which they expressed the corresponding surface molecule. Unbound cells were gently washed off, bound cells were fixed to the arrays and dot patterns were recorded using a DotScan array reader and quantified using DotScan data analysis software. The data obtained show the unique expression profiles of the 7 cell types in the leukaemia cell panel obtained with the DotScan microarray, and the differential capture patterns for these 7 cell types screened against the 498 antibodies in the HLDA8 microarray constructed for this study.

Aberrant promoter methylation of multiple genes throughout the clinico-pathologic spectrum of B-cell neoplasia.

BACKGROUND AND OBJECTIVES: Aberrant promoter methylation targets CpG islands causing gene silencing. We explored aberrant promoter methylation of genes potentially involved in B-cell malignancies and encoding proteins implicated in DNA repair (O6-methylguanine-DNA methyltransferase, MGMT), detoxification of environmental xenobiotics (glutathione S-transferase P1, GSTP1), apoptosis regulation (death associated protein kinase, DAP-k and caspase 8, CASP8) and cell cycle control (p73). DESIGN AND METHODS: Three hundred and seventeen B-cell malignancies were investigated by methylation-specific polymerase chain reaction (MSP) of MGMT, GSTP1, DAP-k, CASP8 and p73 genes. In selected cases, MSP results were matched to protein expression studies by immunohistochemistry or Western blotting. RESULTS: DAP-k promoter methylation occurred at highest frequency in follicular lymphoma (85.0%) and MALT-lymphoma (72.2%). MGMT methylation targeted both precursor B-cell neoplasia (23.8%) and mature B-cell tumors (27.6%). GSTP1 methylation was commonest in hairy cell leukemia (75.0%), follicular lymphoma (55.5%), Burkitt s lymphoma (52.0%), and MALT lymphoma (50.0%). Methylation of p73 and CASP8 was rare or absent. DAP-k and MGMT methylation caused absent protein expression. INTERPRETATION AND CONCLUSIONS: Methylation of MGMT, DAP-k and GSTP1 represents a major pathogenetic event in several B-cell malignancies. In follicular lymphoma and MALT lymphoma, frequent inactivation of the apoptosis extrinsic pathway through DAP-k methylation may reinforce the survival advantage already conferred by deregulation of the intrinsic apoptotic pathway. Inactivation of GSTP1 in gastric MALT lymphoma represents an additional mechanism favoring accumulation of reactive oxygen species and lymphomagenesis. Finally, the frequency of GSTP1 aberrant methylation in diffuse large B-cell lymphoma prompts studies aimed at verifying the prognostic impact of this epigenetic lesion in these lymphomas.

Alemtuzumab.

Alemtuzumab is an unconjugated, humanised, monoclonal antibody directed against the cell surface antigen CD52 on lymphocytes and monocytes. In noncomparative phase I/II studies in patients with B-cell chronic lymphocytic leukaemia (B-CLL) relapsed after or refractory to alkylating agents and fludarabine, intravenous (IV) administration of alemtuzumab 30 mg/day three times weekly for up to 12 weeks was associated with overall objective response (OR) rates of 21-59%. Combining alemtuzumab with fludarabine resulted in ORs >80%. In noncomparative studies in patients with previously untreated B-CLL, subcutaneous (SC) administration of alemtuzumab alone, or IV in combination with fludarabine, was highly effective, achieving OR rates of around 90%. IV alemtuzumab was active in patients with chemotherapy-resistant/relapsed T-cell prolymphocytic leukaemia, with reported OR rates of 24-76%. Alemtuzumab has been incorporated in novel conditioning regimens designed to facilitate stem cell transplantation in haematological malignancies. Adverse events with alemtuzumab are predictable and manageable. 'First-dose' flulike symptoms, frequently seen after IV infusion, can be managed by (pre)medication and minimised by dose escalation (or SC injection). Anti-infective prophylaxis is mandatory. Cytopenias are transient, although red blood cell and platelet support may be required.

CD5-negative, CD10-negative small B-cell leukemia: variant of chronic lymphocytic leukemia or a distinct entity?

CD5- and CD10-negative chronic lymphocytic leukemias are quite uncommon as compared to the CD5-positive CLL. We reviewed 250 sequential cases of peripheral blood lymphocytosis to characterize cases of small B-cell lymphoproliferative disorders, submitted with a clinical diagnosis of chronic lymphocytic leukemia exhibiting a non-classic immunophenotypic profile. Six cases of CD5-, CD10-negative chronic lymphocytic leukemias and no tissue involvement were identified that revealed high-density surface-membrane immunoglobulin and CD20 expression, with variable expression of CD11c, CD23, and CD25. Most had a profound leukocytosis (mean WBC 180 x 10(9)/L) with proliferation of mature-appearing lymphocytes. Subsequent bone marrow biopsies showed diffuse infiltration by neoplastic cells in all evaluated patients. The clinical course appeared indolent, with follow-up revealing three patients alive (survival time 38-68 months), while two died of unrelated causes and one was lost to follow-up soon after diagnosis. These cases may represent somewhat unusual chronic lymphoproliferative disorders, with morphologic features and immunophenotypic profile not readily classifiable, but which are certainly atypical for classic chronic lymphocytic leukemia. Some of these features are reminiscent of those seen in marginal-zone lymphoma. However, it is most unusual for this known to be tissue-based disease to present primarily as leukemia rather than lymphoma.

Identification of cyclin D1 mRNA overexpression in B-cell neoplasias by real-time reverse transcription-PCR of microdissected paraffin sections.

PURPOSE: Overexpression of cyclin D1 mRNA and protein as a result of the chromosomal translocation t(11;14)(q13;q32) is a highly specific molecular marker of mantle cell lymphoma, but cyclin D1 dysregulation can also be found in other B-cell neoplasias. The aim of the study was to develop a precise and reliable tool for quantitation of cyclin D1 mRNA suitable for archival clinical specimens. EXPERIMENTAL DESIGN: A real-time reverse transcription-PCR (RT-PCR) assay was used to quantitate cyclin D1 mRNA copy numbers. Using 2000 microdissected cells as template, 104 formalin-fixed, paraffin-embedded lymph node, spleen, and decalcified bone marrow biopsies from a panel of 95 cases of B-cell non-Hodgkin's lymphomas (B-NHLs) were analyzed. In addition, cyclin D1 protein expression was assessed by immunohistochemistry. RESULTS: Strong cyclin D1 mRNA overexpression was detected in mantle cell lymphomas (23 of 23), hairy cell leukemias (5 of 19), and multiple myelomas (7 of 23) with particularly high levels in 2 of the latter cases. Intermediate transcript levels were found in 5 of 23 multiple myelomas and 7 of 19 hairy cell leukemias. B-cell chronic lymphocytic leukemias (10 of 10), follicular lymphomas (9 of 9), mucosa-associated lymphoid tissue lymphomas (5 of 5) and reactive lymphoid tissues with the exception of normal spleen had no or very low cyclin D1 expression. In comparison with real-time RT-PCR, immunohistochemistry showed a lower level of sensitivity, more variability, and did not allow accurate quantitation. CONCLUSIONS: Real-time RT-PCR for cyclin D1 mRNA is an excellent tool for the differential diagnosis of B-NHLs and, in combination with microdissection, a powerful approach for retrospective trials using archival clinical specimens as tissue source. Furthermore, real-time RT-PCR may help to identify subgroups of B-NHLs according to cyclin D1 mRNA copy numbers and to investigate the possible influence of different chromosomal breakpoints on cyclin D1 expression.

Recurrent B-cell neoplasms after Rituximab therapy: an immunophenotypic and genotypic study.

Rituximab has been widely used to treat relapsing or advanced stage B-cell neoplasms with an efficacy of about 50%. However, approximately 40-50% of Rituximab treated patients will recur. It is not clear whether these recurrent diseases have the same immunophenotype as that of the original tumors. At the City of Hope, we treated 91 cases of CD20-positive B-cell neoplasms with Rituximab in combination with chemotherapy and hematopoietic stem cell transplantation between August 1999 and December 2000. Thirty-five of 91 patients (38%) experienced recurrence during the time period within one year from treatment. Tumor cells from all of the recurrent patients expressed one or more B cell antigens (CD19, CD20, CD22, CD45RA, or CD79a). However, thirteen of 35 recurrent cases showed aberrant loss of CD20 expression (37%) by immunohistochemical or flow cytometric studies. Pre- and post-Rituximab treated tumor cell DNA was successfully extracted from archival paraffin sections, hematoxylin and eosin (H and E) stained slides, smears, or frozen cells in 10 of 13 CD20 negative recurrent cases. PCR studies for immunoglobulin (Ig) heavy chain gene rearrangements were performed in all these cases. Five cases showed identical Ig heavy chain gene rearrangements in the paired specimens. PCR assay for Ig kappa (kappa) gene rearrangement was performed in the five paired specimens lacking detectable Ig heavy chain gene rearrangements; 2 of them showed identical Igkappa gene rearrangements. Three pairs showed unmatched Ig heavy chain and Igkappa gene rearrangements, probably due to poor quality of recovered DNA. Aberrant loss of CD20 antigens may be a mechanism of treatment resistance and should be considered in the immunophenotyping of recurrent Rituximab-treated B-cell neoplasms; therefore, a panel of B cell markers is recommended for the immunologic diagnosis of recurrent B cell malignancies after Rituximab therapy. Seven of ten pairs of recurrent CD20-negative cases showed identical Ig heavy chain and Igkappa gene rearrangements by PCR assay, strongly suggesting that the pre- and post-Rituxan treated B cell neoplasms are clonally-related.

The classification of lymphomas and leukemias.

Classifications of lymphomas and leukemias have developed from two distinct clinical needs - to understand the natural history of these diseases in order to predict outcome and to make treatment decisions in a rational fashion. The utility of classifications for research on etiology of these diseases has not guided their development in the past. The classification of leukemias and lymphomas has undergone dramatic changes with increasing understanding of the development of the normal immune cells. Historically, the first entity to be recognised was Hodgkin disease. Other malignancies of the lymphatic system were then called 'Non-Hodgkin Lymphomas' (NHL), a distinction that remains valid even today. Cancers that tend not to form distinct masses but usually present with a raised white blood cell count were called leukemias. As knowledge has improved, however, the early juxtaposition of leukemias versus lymphomas has lost relevance, since often the same entity can present in either way. With better understanding the terms 'lymphosarcoma' and 'reticulosarcoma', which were earlier widely applied have been replaced by more precise terminology. Different classifications have been put forward over the years. The 'Revised European and American Classification of Lymphoid Neoplasms' and the derived WHO classification are structured to mirror normal B/T-cell differentiation. In these modern classifications, distinct disease entities are defined based on the combination of morphology, immunological and molecular techniques and clinical features. The proposed major groups of lymphoid neoplasms are B-cell lymphomas/leukemias, T/Natural Killer-cell lymphomas/leukemias and Hodgkin disease. About 20 entities are recognised. This provides for the first time a truly international view of lymphomas and leukemias. It has emerged that such a classification can be used successfully by expert hematopathologists and yields highly reproducible results. It is also clear that no single marker, be it morphology, genetic analysis or immunophenotyping can be used as the 'gold standard' for diagnosis but that a combination of techniques is needed.

[Small cell B-cell lymphomas: guidelines for differential diagnosis]. / Kleinzellige B-Zell-Lymphome: Differentialdiagnostische Leitlinien.

Similar to the R.E.A.L-System, the small cell B-cell lymphomas of the new WHO classification consist of chronic lymphocytic leukaemia of B cell type, mantle cell lymphoma, follicular lymphoma, lymphoplasmocytic lymphoma/immunocytoma, hairy cell leukaemia, as well as plasmacytoma. The only major difference between the WHO- and the REAL-classification is the consideration of prolymphocytic leukaemia as a single disease entity in the former system. All the above-mentioned lymphomas arise from B cells of varying stages of differentiation and, therefore, often demonstrate architectural, cytological and immunophenotypic characteristics of their normal physiological counterparts. Consideration of tumour cell growth pattern, -cytology, -immunophenotype and -growth fraction, together with the presence and consistency of the reactive cell infiltrate, usually leads to categorisation of a lymphoma in the majority of cases. The molecular biological characteristics of follicular lymphoma and mantle cell lymphoma are the best defined of the small cell B-cell lymphomas. Chromosomal translocations involving the immunoglobulin heavy chain genes and the bcl-2 gene or Cyclin D1 gene, respectively, probably belong to the initial changes in a cell, which, together with several subsequent unidentified genetic alterations, lead to the development of these tumours. Although nodal small cell B-cell lymphomas are usually diagnosed at an advanced stage of the disease, the progression of the disease--with the exception of mantle cell lymphomas--is often indolent. As a result, the small cell B-cell lymphomas were previously considered as "low-grade" Non-Hodgkin lymphomas in the Kiel classification. However, since the progress of a lymphoma subtype can be heterogeneous and since mantle cell lymphomas cannot really be considered as "low-grade" tumours, "umbrella grading" of lymphomas has been discarded in the WHO classification, with emphasis being placed on grading within a lymphoma disease entity. In the following pages, the characteristics important for the diagnosis and categorisation of the small cell B-cell lymphomas will be summarised. Further, we present information regarding the molecular biological and clinical characteristics of these lymphomas.

Mature B-cell lymphoma/leukemia in children and adolescents: intergroup pathologist consensus with the revised European-American Lymphoma Classification.

BACKGROUND: The Revised European-American Lymphoma (R.E.A.L.) Classification criteria were evaluated in the international protocol FAB LMB 96 Treatment of Mature B-cell Lymphoma/Leukemia: A SFOP LMB 96/CCG-5961/UKCCSG NHL 9600 Cooperative Study. This includes B-lineage lymphomas: Burkitt's lymphoma (including ALL-L3); high-grade B-cell lymphoma, Burkitt-like; diffuse large B-cell lymphoma (excluding anaplastic large cell Ki-1 lymphoma). PATIENTS AND METHODS: Cases were independently reviewed by eight hematopathologists from the three cooperative national groups (two SFOP, two CCG, four UKCCSG), without prior discussion of classification criteria or guidelines for case rejection. Consensus diagnosis was determined by each national cooperative group, and final consensus diagnosis established when at least two national consensus diagnoses were in agreement, or following group agreement at a multiheaded microscope. RESULTS: Two hundred eight cases were reviewed, with final consensus diagnosis established in two hundred three. The percent agreement of each group's national consensus diagnosis with final consensus diagnosis was 86%, 86% and 71%. The percent agreement of the group's national consensus diagnosis with final consensus diagnosis for Burkitt's and diffuse large B-cell lymphoma were 88% and 80%, respectively, but only 42% for Burkitt-like lymphoma. CONCLUSIONS: International panel review of mature B-cell lymphoma/leukemia in children and adolescents highlighted difficulties in subclassification, particularly with Burkitt-like, which is a 'provisional entity' in the R.E.A.L. Classification. The absence of previous discussion of classification and guidelines for case rejection may in part explain the discrepancy between pathologists. These results underline that morphology may need to be complemented by other studies, such as molecular genetic and cytogenetics, to discriminate between the mature B-cell lymphomas.