Pathology of lymphoma progression

Progression of follicular lymphoma and related entities: Report from the 2021 SH/EAHP Workshop

OBJECTIVES

The 2021 Society for Hematopathology and European Association for Haematopathology Workshop addressed the molecular and cytogenetic underpinnings of transformation and transdifferentiation in lymphoid neoplasms.

METHODS

Session 4, "Transformations of Follicular Lymphoma," and session 5, "Transformations of Other B-Cell Lymphomas," included 45 cases. Gene alteration analysis and expression profiling were performed on cases with submitted formalin-fixed, paraffin embedded tissue.

RESULTS

The findings from session 4 suggest that "diffuse large B-cell lymphoma/high-grade B-cell lymphoma with rearrangements of MYC and BCL2" is a distinct category arising from the constraints of a preexisting BCL2 translocation. TdT expression in aggressive B-cell lymphomas is associated with MYC rearrangements, immunophenotypic immaturity, and a dismal prognosis but must be differentiated from lymphoblastic -lymphoma. Cases in session 5 illustrated unusual morphologic and immunophenotypic patterns of transformation. Additionally, the findings support the role of cytogenetic abnormalities-specifically, MYC and NOTCH1 rearrangements-as well as single gene alterations, including TP53, in transformation.

CONCLUSIONS

Together, these unique cases and their accompanying molecular and cytogenetic data suggest potential mechanisms for and unusual patterns of transformation in B-cell lymphomas and indicate numerous opportunities for further study.

Overall and event-free survival of childhood lymphoma in Greece: analysis of harmonized clinical data over a 24-year active registration period

We assessed event-free (EFS) and overall (OS) survival in 676 incident cases of childhood Hodgkin (HL) and non-Hodgkin (NHL) lymphoma actively registered in Greece (1996-2019). HL-OS_5-year was 96% and NHL-OS_5-year 85%, whereas HL-EFS_5-year was 86% and NHL-EFS_5-year was 81%, notably similar to the respective OS rates (HL: 95%, NHL: 85%) in developed countries. For HL, older age at diagnosis, high maternal education and close proximity to treatment centers were linked to remarkably favorable outcomes. By contrast, stage IV patients showed worse OS and EFS. HL patients with low levels of hemoglobin were associated with worse EFS (hazard ratio: 2.81, 95% confidence intervals: 1.09-7.22). OS (76%) and EFS (73%) were poor among high-risk NHL patients and those with increased LDH (71%). The identified predictors of poor disease outcome point to the need for intensification of individualized treatments. Ongoing clinical cancer registration entailing clinical components could contribute to use of state-of-the-art treatments.

Multimodality imaging of indolent B cell lymphoma from diagnosis to transformation: what every radiologist should know

Indolent B cell lymphomas are a group of lymphoid malignancies characterized by their potential to undergo histologic transformation to aggressive lymphomas. While different subtypes of indolent B cell lymphomas demonstrate specific clinical and imaging features, histologic transformation can be suspected on cross-sectional imaging when disproportionate lymph node enlargement or new focal lesions in extranodal organs are seen. On PET/CT, transformed indolent lymphoma may show new or increased nodal FDG avidity or new FDG-avid lesions in different organs. In this article, we will (1) review the imaging features of different subtypes of indolent B cell lymphomas, (2) discuss the imaging features of histologic transformation, and (3) propose a diagnostic algorithm for transformed indolent lymphoma. The purpose of this review is to familiarize radiologists with the spectrum of clinical and imaging features of indolent B cell lymphomas and to define the role of imaging in raising concern for transformation and in guiding biopsy for confirmation.

A Rare Case of Composite Dural Extranodal Marginal Zone Lymphoma and Chronic Lymphocytic Leukemia/Small Lymphocytic Lymphoma

Background

Primary extranodal marginal zone lymphoma (MZL) of the dura is a rare neoplastic entity in the central nervous system (CNS).

Methods

We used literature searches to identify previously reported cases of primary dural MZL. We also reviewed clinical, pathologic, and radiographic data of an adult patient with concurrent dural MZL and chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL).

Results

We identified 104 cases of dural MZL in the literature. None of them presented concurrently with another type of non-Hodgkin lymphoma. This is the first report of composite lymphoma consisting of dural MZL and CLL/SLL in the bone marrow and lymph nodes.

Conclusion

Primary dural MZL is a rare, indolent low-grade CNS lymphoma, with a relatively good prognosis. Its treatment is multidisciplinary and often requires surgical intervention due to brain compression, along with low to moderate doses of radiotherapy and/or systemic chemotherapy.

Follicular lymphoma grade 3: review and updates

Follicular lymphoma (FL), Grade 3, is recognized as a distinct entity in the World Health Organization classification of lymphoma. It is further classified into Grade 3a and Grade 3b depending on the Bernard cell counting system and percentage of centroblasts. Grade 3 has molecular and genetic characteristics that distinguish it from other grades of FL. There is confusion and misunderstanding about the natural history and clinical course of Grade 3a and 3b because some studies indicate them as having indolent behavior and others describe more aggressive biology. The purpose of this article is to understand the concept of Grade 3 FL, especially the fundamental differences between Grade 3a and Grade 3b FL. Grade 3 FL is still an evolving subclass in FL and the practicing physician should understand the aggressive nature of Grade 3b, which typically requires timely attention, compared with Grade 3a. Grade 3a FL has more indolent characteristics but can possibly progress to Grade 3b and/or transform to diffuse large B-cell lymphoma at a future time. Nevertheless, large prospective studies are missing for an optimal evidence-based management approach for patients with Grade 3 FL at this time.

[Grey zone lymphomas: limitations of the classification of aggressive B-cell lymphomas]

Grey zone lymphomas are lymphatic tumors that cannot be assigned to a defined lymphoma entity due to morphological, clinical or genetic reasons. As a defining criterion they present with features of two overlapping entities or features that are intermediate. Such lymphomas may represent a grey zone in the differentiation between indolent and aggressive lymphomas. Often they may show morphological features of one entity but be more related to another entity with respect to the immunophenotype and/or genetic constitution, such as lymphomas in the grey zone between primary mediastinal large B-cell lymphoma and primary nodal diffuse large B-cell lymphoma. The B-cell lymphoma, unclassified, with features intermediate between diffuse large B-cell lymphoma and Burkitt lymphoma has recently been recognized as a provisional category in the updated WHO 2008 classification of malignant lymphomas. This corresponds to a practical lymphoma category that obviously contains several entities with a Burkitt-like appearance and aggressive clinical behavior. Genetically, tumors in this category are frequently characterized by an atypical MYC translocation and complex karyotypic alterations. As yet, no adequate therapy concept exists.

EZH2 and CD79B mutational status over time in B-cell non-Hodgkin lymphomas detected by high-throughput sequencing using minimal samples

BACKGROUND: Numerous genomic abnormalities in B-cell non-Hodgkin lymphomas (NHLs) have been revealed by novel high-throughput technologies, including recurrent mutations in EZH2 (enhancer of zeste homolog 2) and CD79B (B cell antigen receptor complex-associated protein beta chain) genes. This study sought to determine the evolution of the mutational status of EZH2 and CD79B over time in different samples from the same patient in a cohort of B-cell NHLs, through use of a customized multiplex mutation assay.

METHODS: DNA that was extracted from cytological material stored on FTA cards as well as from additional specimens, including archived frozen and formalin-fixed histological specimens, archived stained smears, and cytospin preparations, were submitted to a multiplex mutation assay specifically designed for the detection of point mutations involving EZH2 and CD79B, using MassARRAY spectrometry followed by Sanger sequencing.

RESULTS: All 121 samples from 80 B-cell NHL cases were successfully analyzed. Mutations in EZH2 (Y646) and CD79B (Y196) were detected in 13.2% and 8% of the samples, respectively, almost exclusively in follicular lymphomas and diffuse large B-cell lymphomas. In one-third of the positive cases, a wild type was detected in a different sample from the same patient during follow-up.

CONCLUSIONS: Testing multiple minimal tissue samples using a high-throughput multiplex platform exponentially increases tissue availability for molecular analysis and might facilitate future studies of tumor progression and the related molecular events. Mutational status of EZH2 and CD79B may vary in B-cell NHL samples over time and support the concept that individualized therapy should be based on molecular findings at the time of treatment, rather than on results obtained from previous specimens. Cancer (Cancer Cytopathol) 2013;121:377–386. © 2013 American Cancer Society.

Mantle cell lymphoma as a component of composite lymphoma: clinicopathologic parameters and biologic implications

Composite lymphoma is a rare circumstance in which 2 or more distinct types of lymphoma occur in a single anatomical location. Although composite lymphoma has been increasingly identified with the advent of molecular genetic techniques, this topic has only rarely been a specific focus of the medical scientific literature. In this review, we focus on mantle cell lymphoma occurring as a major pathologic component of composite lymphoma and emphasize the clinicopathologic features of these tumors and associated biologic implications. To date, 26 cases of composite lymphoma including a component of mantle cell lymphoma have been previously published. Issues of clonal relatedness between the individual lymphoma components and emerging biologic implications as well as potential diagnostic pitfalls are evaluated.

Parallel gene expression profiling of mantle cell lymphoma - how do we transform 'omics data into clinical practice

DNA microarray technology has been a valuable tool to provide a global view of the changes in gene expression that characterize different types of B cell lymphomas, both in relation to clinical parameters but also in comparison with the non-malignant counterparts. The number of transcripts that can be analyzed on an array has dramatically increased, and now most commercially available arrays cover the whole genome, enabling overall analysis of the transcriptome.The backside of collecting this massive amount of information is that even after strict data filtering, it is impossible to do follow-up studies on all findings. Down-stream analysis is time-consuming and when performing confirmatory experiments on the protein level, the experiments are in most cases restricted to proteins recognized by commercially available reagents. Furthermore, since gene expression data is a comparative method not only are the experimental set-up but also the characteristics of both the sample and reference crucial for our ability to answer the questions posed. Thus, initial care must be taken in the design of the experiment and the preparation of the samples.The aim of this review is to discuss the progress in mantle cell lymphoma research enabled by gene expression analysis and to pinpoint the difficulties in making efficient use of the generated data to provide a fast and accurate clinical diagnosis, efficient stratification of patients into disease sub-groups and improved therapy.

Transformation of follicular lymphoma

Histological transformation of follicular lymphoma (FL) to a more aggressive non-Hodgkin's lymphomas is a pivotal event in the natural history of FL and is associated with poor outcome. While commonly observed in clinical practice and despite multiple studies designed to address its pathogenesis, the biology of this process represents an enigma. In this chapter we present a state of the art review summarizing the definition of histologic transformation, its incidence, pathogenesis, clinical manifestations, treatment and outcome. Furthermore, we specifically emphasize gaps in our knowledge that should be addressed in future studies.

Usefulness of multiparametric flow cytometry in detecting composite lymphoma: study of 17 cases in a 12-year period

Composite lymphoma (CL) is a rare occurrence of 2 or more morphologically and immunophenotypically distinct lymphoma clones in a single anatomic site. A retrospective analysis of 1,722 solid tissue samples clinically suggestive of lymphoma was carried out in our institute during a 12-year period to evaluate the efficacy of flow cytometry (FC) in identifying CL. We report 17 CL cases. A strong correlation between morphologic findings and FC was observed in 13 cases (76%). In the 4 cases diagnosed as non-Hodgkin lymphoma plus Hodgkin lymphoma, although FC did not detect Reed-Sternberg cells, it accurately identified the neoplastic B- or T-cell component. In 3 cases, FC indicated the need to evaluate an additional neoplastic component that was not morphologically evident. Our data demonstrate that FC immunophenotyping of tissues may enhance the performance of the diagnostic morphologic evaluation of CL. To the best of our knowledge, this is the first report in the literature of a wide series of CL studied also by FC.

Prognostic Factors in Follicular Lymphoma

Follicular lymphoma (FL) is one of the most common types of non-Hodgkin's lymphoma. It is usually diagnosed at an advanced stage, for which many treatment options exist, however, no curative standard therapy has been identified. The outcome is highly variable with a median survival of approximately 10 years. The life expectancy of patients with FL has been extended with the use of rituximab, a monoclonal antibody targeting the CD20 antigen on FL cells, but there remains a group of patients who fail to respond to chemoimmunotherapy and die early of their disease. Transformation of FL to an aggressive histology is an important event with high morbidity and mortality. The Follicular Lymphoma International Prognostic Index has become the clinically useful prognostic tool, but gives only a rough estimate of expected outcome. There is a need for useful biomarkers for prediction of the disease course of single patients to individualize therapy, especially in the new era of chemoimmunotherapy.

PRL-2 increases Epo and IL-3 responses in hematopoietic cells

Dual specificity protein tyrosine phosphatase PRL-2 is overexpressed in pediatric acute myeloid leukemia (AML) and is located at human chromosome 1p35, a region often rearranged or amplified in malignant lymphoma and B-cell chronic lymphocytic leukemia (B-CLL). Little is known of the significance of PRL-2 expression in hematopoietic malignancies. Herein we demonstrated that ectopic expression of PRL-2 in murine pre-B-cell line Baf3ER and mouse bone marrow cells induced key features associated with malignant progression and metastasis. PRL-2-transfected Baf3ER cells had augmented growth responses to hematopoietic growth factors Epo or IL-3 with shortened cell cycle, reduced requirement (5x) for Epo in cell survival, increased cell migration (3x), reduced cell adhesion (5x), and conversion to an immature cell morphology in association with increased expression (3x) of stem cell marker Bmi-1. When transduced into mouse bone marrow cells, PRL-2 increased Epo-induced colony formation (4x) and gave rise to larger colonies. These observations provide evidences implicating PRL-2 as a pathogenic molecule in hematopoietic malignancies and suggest its potential as a novel therapeutic target.

Composite marginal zone B-cell lymphoma and classical Hodgkin's lymphoma: a clinicopathological study of 12 cases

AIMS

Classical Hodgkin's lymphoma (cHL) rarely coexists as composite lymphoma with B-cell non-Hodgkin's lymphoma (B-NHL). We characterized 12 cases of composite marginal zone B-cell lymphoma (MZBL) and cHL by immunohistochemistry and molecular biology.

METHODS AND RESULTS

Eight patients had gastric MZBL of mucosa-associated lymphoid tissue (MALT)-type, in five cases with a diffuse large B-cell lymphoma component. Concurrent cHL was observed either in the stomach wall, regional, or distant lymph nodes. One patient each had composite pulmonary/thyroid MZBL of MALT-type and cHL. In two cases, nodal composite MZBL and cHL was observed. cHL displayed features of mixed cellularity type in 10 cases, while in two cases only scattered Hodgkin- and Reed-Sternberg (H/RS) cells were noted. H/RS cells expressed CD30, multiple myeloma oncogene 1 protein (MUM1P), p53 (100%), CD15 (58%), CD20 (58%) and Epstein-Barr virus-associated LMP1 (50%). No t(11;18)(q21;q21) was detected in composite MZBL of MALT-type and cHL.

CONCLUSIONS

MZBL and cHL may occur as composite lymphoma, possibly reflecting clonal lymphoma progression. Derivation from extranodal MZBL of MALT-type should be excluded in cases in which a diagnosis of primary extranodal cHL is considered.

Richter syndrome: biology, incidence, and therapeutic strategies

Richter's transformation denotes the development of high-grade non-Hodgkin lymphoma, prolymphocytic leukemia, Hodgkin disease, or acute leukemia in patients with chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma. A search of published articles in Medline (PubMed) and abstracts from professional meetings was performed. An electronic database search of patients with CLL at The University of Texas M. D. Anderson Cancer Center (Houston, TX) determined the incidence of Richter syndrome (RS) in patients with CLL between 1992 and 2002. RS occurs in approximately 5% of patients with CLL. The large cells of RS may arise through transformation of the original CLL clone or represent a new neoplasm. RS may be triggered by viral infections, such as Epstein-Barr virus. Trisomy 12 and chromosome 11 abnormalities are more frequent in patients with RS than in the overall population of patients with CLL. Multiple genetic defects, such as mutations of the p53 tumor suppressor gene, p16INK4A, and p21, loss of p27 expression, deletion of retinoblastoma, increased copy number of C-MYC, and decreased expression of the A-MYB gene, have been described. These abnormalities may cause CLL cells to proliferate and-by facilitating the acquisition of new genetic abnormalities-to transform into RS cells. Therapeutic strategies include intensive chemotherapy, monoclonal antibodies, and stem cell transplantation. The response rates range from 5% to 43% (complete response, 5-38%), and the median survival duration ranges from 5 months to 8 months. In conclusion, RS may be triggered by viral infections or by genetic defects. Current treatments are aggressive, but prognosis is poor. Novel curative treatment strategies are needed.

Highly efficient delivery of p16 antitumor peptide into aggressive leukemia/lymphoma cells using a novel transporter system

Molecular targeting of hematopoietic malignancies has been generally hindered by technological obstacles to gene delivery in the neoplastic cells. The development of peptide delivery systems based on protein transduction domains has recently gained attention as a means of potentially overcoming these impediments. Here, we present a novel peptide transporter system that increases the efficiency of peptide delivery more than 10 times compared with the previous methods. The transporter, Wr-T, has an enlarged hydrophobic pocket consisting of triple tryptophan-rich domains fused with nine d-enantiomer polyarginines (r9) via Gly-Pro-Gly spacer, which serves to augment delivery of a cargo peptide. Wr-T–mediated transport of p16INK4a functional peptide dramatically inhibits growth of highly aggressive leukemia/lymphomas by up to 80% through restoration of p16 function. The Wr-T system thus represents a highly effective approach to cargo peptide delivery with the potential for substantially developing p16 peptide–based therapy for hematopoietic malignancies.

Relationship between the mutational status of VH genes and pathogenesis of diffuse large B-cell lymphoma in Richter's syndrome

Patients with chronic lymphocytic leukemia (CLL) may develop diffuse large B-cell lymphoma (DLBL), also known as Richter's syndrome. Mutational status of immunoglobulin (Ig) heavy-chain variable region (VH) genes have prognostic impact in CLL. Patients with mutated VH genes have a stable disease, whereas patients with unmutated VH gene have more aggressive disease. The mutational status of CLLs that transform to DLBL is unknown. To reveal whether Richter's syndrome occurs in CLLs with mutated or unmutated VH genes, we have performed mutational analysis on serial specimens from eight patients. CLL and DLBL tumorclones were identical in five cases and they were different in three cases. Six CLLs expressed unmutated and two cases expressed mutated VH genes. In five of the six unmutated CLLs, the DLBL clones evolved from CLL tumorclones and the VH genes expressed by DLBLs were also unmutated. In one unmutated and two mutated CLLs, the DLBLs expressed mutated VH genes, but in these three cases the DLBL tumorclones developed as independent secondary neoplasm. These results suggest that Richter's syndrome may develop in both mutated or unmutated CLLs, but clonal transformation of CLL to DLBL occur only in the unmutated subgroup of CLL.

Lymph node reticulum cell neoplasm with progression into cytokeratin-positive interstitial reticulum cell (CIRC) sarcoma: a case study

AIMS

To detail on sequential biopsies the morphological and immunohistochemical features of a case of primary lymph nodal fibroblastic reticulum cell (FBRC) tumour which progressed into a clinically aggressive cytokeratin-positive interstitial reticulum cell (CIRC) sarcoma.

METHODS AND RESULTS

A 70-year-old female underwent surgical excision of an enlarged submandibular lymph node. The nodal architecture was effaced by a neoplastic proliferation of medium to large cells, round to oval to spindle in shape, growing in a storiform pattern. The tumour stained for vimentin, CD68, factor XIIIa, alpha1-antitrypsin, fascin and actin. Dendritic and endothelial cell markers were negative. A diagnosis of FBRC tumour was made by combining pathological and clinical data. The patient received no therapy but 5 months later the tumour relapsed, exhibiting a deceptively pleomorphic cytology, phenotypic changes (strong cytokeratin positivity), intense p53 expression and aggressive clinical course with fatal outcome. In-situ hybridization for Epstein-Barr virus was negative.

CONCLUSIONS

We speculate that the morphological changes and p53 expression of the relapsing neoplasm might reflect tumour cell dedifferentiation, in keeping with the aggressive clinical course. The intense p53 expression suggests that this oncoprotein might also play a role in reticulum cell tumorigenesis.

Comparative studies of somatic and ongoing mutations in immunoglobulin heavy-chain variable region genes in diffuse large B-cell lymphomas of the stomach and the small intestine

CONTEXT

Many diffuse large B-cell lymphomas (DLBCLs) of the stomach are believed to represent high-grade transformation of low-grade marginal zone B-cell lymphoma of mucosa-associated lymphoid tissue type, which is of memory B-cell origin, displaying evidence for positive antigen selection and a low level of ongoing somatic mutation of the rearranged immunoglobulin heavy-chain variable region (V(H)) genes. The pattern of somatic mutation has been studied little in intestinal DLBCLs.

OBJECTIVE

To assess evidence for antigen selection and the levels of ongoing mutation, we analyzed the ratio of replacement to silent mutations, as well as the frequency of intraclonal sequence variation in gastric and small intestinal DLBCLs that showed no concomitant low-grade component.

DESIGN

Genomic DNA was extracted from formalin-fixed paraffin blocks of gastric (n = 6) and small intestinal (n = 6) DLBCLs. The complementarity-determining region 2 and framework region 3 sequences (<200 base pairs) of the rearranged immunoglobulin V(H) gene were obtained from polymerase chain reaction-amplified product, and the ratio of replacement-to-silent mutations and the frequency of intraclonal sequence variation were determined.

RESULTS

Clustering of replacement mutations in complementarity-determining region 2 with a high (>2.9) ratio of replacement-to-silent mutations was observed in 5 gastric DLBCLs, whereas it was recognized in only 1 intestinal DLBCL. Intraclonal sequence variation was observed in 6 intestinal and 5 gastric DLBCLs. The frequency of ongoing mutation was much higher in the intestinal (median, 0.33%) than in the gastric DLBCLs (median, 0.13%), but the difference was not statistically significant (P =.09).

CONCLUSIONS

The mutation pattern was consistent with positive antigen selection in gastric DLBCLs, but not in the intestinal tumors. Ongoing mutation was much more frequent in the intestinal than in the gastric DLBCLs. These findings suggest that positive antigen selection plays a major role in a significant proportion of gastric tumors, whereas germinal center reaction with aberrant mutation is important in small intestinal DLBCLs.

Immunohistochemical analysis of B-cell lymphoma using tissue microarrays identifies particular phenotypic profiles of B-cell lymphomas

AIMS

To validate the applicability of tissue microarray (TM) in immunohistochemical profiling of B-cell lymphoma and to identify particular phenotypic profiles of B-cell neoplasms.

METHODS AND RESULTS

Eighty-two diffuse large B-cell lymphomas (DLBL), 54 follicular lymphomas (FL) and 74 mantle cell lymphomas (MCL) were arrayed. Immunohistochemical stains of TM were compared with immunostains of conventional, formalin-fixed and frozen material sections. Concordant staining results were obtained in more than 88% of cases for CD20, CD3, CD5, CD10, CD23, Bcl-2, IgD, secretory differentiation, p53 and p21 expression. Prognostically relevant hot-spot expression of Ki67 yielded concordant results in 71%. Applying TM for characterization of p27KIP1 expression, both typical and blastoid MCL only rarely showed p27KIP1 expression (9% and 15%), whereas 32% of nodal DLBL were p27KIP1-positive, irrespective of high proliferative activity. Among 22 B-cell lymphomas investigated genetically, a p53 + p21- immunophenotype in >20% of tumour cells correlated with p53 locus deletion.

CONCLUSIONS

Lymphoma TM allows for immunohistochemical profiling of human B-cell lymphoma with a comparable accuracy to immunohistochemical studies performed on conventional tissue sections. Nodal DLBLs showed significantly more frequent expression of IgD and p27KIP1 than extranodal DLBL. MCL and DLBL frequently showed aberrant p27KIP1 expression. A p53 + p21- immunophenotype in >20% of tumour cells in B-cell non-Hodgkin's lymphoma correlates with p53 gene deletion.

Critical evaluation of Bcl-6 protein expression in diffuse large B-cell lymphoma of the stomach and small intestine

Diffuse large B-cell lymphoma (DLBCL) of the gastrointestinal tract is heterogeneous, including mucosa-associated lymphoid tissue (MALT) origin and non-MALT, and they are indistinguishable. MALT lymphoma is a tumor of a post-germinal center (GC) memory B-cell origin, which is negative for Bcl-6 protein expression in low-grade but may become positive in high-grade tumors. Because Bcl-6 expression patterns in lymphoma of GC and non-GC B-cell origins have recently been characterized and CD10 is generally regarded as a specific marker for GC B cells, we critically evaluated gastric and small intestinal DLBCLs to see whether it is possible to identify tumor of GC B-cell origin by immunostaining in archival specimens. High-grade MALT lymphoma (H-ML) of the stomach (n = 20) was defined by the presence of a concomitant lymphoepithelial lesion and/or follicular colonization; and DLBCLs de novo, both gastric (n = 31) and intestinal (n = 21), were defined by the absence of the above features. Immunostaining for Bcl-6 and CD10 was done using formalin-fixed, paraffin-embedded sections and was examined independently by three pathologists. Staining for Bcl-6 was positive (>10% of tumor cells) in 55 of 72 cases. However, two distinct patterns were recognized among those positive: diffusely dense (>75%) and sporadic (<75%). The former was further characterized by a consistency of Bcl-6+ tumor cell density at any given area, resembling the staining pattern of the GC or follicular lymphoma (FL) (GC/FL pattern), whereas the latter was, besides less dense population, by variable density from area to area. The GC/FL pattern was observed in 36% and 38% of gastric and intestinal DLBCLs de novo, respectively, but in none of the gastric H-ML. CD10 was positive in 12 of 71 cases (17%), all coexpressing Bcl-6. CD10+ tumors were more frequent in the intestinal (33%) than in gastric DLBCLs ( approximately 15%). Significantly, CD10 expression was observed in three gastric H-MLs, including one that displayed a distinct lymphoepithelial lesion.

IN CONCLUSION

1). tumors showing a diffusely dense pattern of Bcl-6 expression should be distinguished from those showing a sporadic pattern; for the former most likely represents the tumor of GC B-cell derivation, and the latter non-GC, including MALT lymphoma; 2). tumor of GC B-cell origin thus defined accounted for about one third of gastric as well as intestinal DLBCLs de novo but none of the gastric H-ML; and 3). CD10 expression can be seen in MALT lymphomas and should not be used as the marker for GC B cells.

Follicular lymphoma with marginal zone differentiation: cytogenetic findings in support of a high-risk variant of follicular lymphoma

AIMS

The pathogenesis and clinical significance of marginal zone differentiation in follicular lymphoma remains to be determined, although genetic alterations are likely to be important determinants of both. We therefore report the cytogenetic findings in three cases of follicular lymphoma with marginal zone differentiation studied by routine karyotyping and in-situ hybridization.

METHODS AND RESULTS

The morphology and immunophenotype of each case was typical of follicular lymphoma displaying marginal zone differentiation. Karyotyping, performed on GTL-banded preparations of cell cultures derived from fresh lymph node tissue, revealed a complex karyotype in all three cases, including t(14;18)(q32;q21) and abnormalities associated with progression and/or transformation of follicular lymphoma. In addition, trisomy 3 was found in one case and translocations between the q27-29 region of chromosome 3 and chromosome 2 in the other two cases; the latter was identified only in subclones derived from less complex stem lines possessing t(14;18). In-situ hybridization, performed on sections cut from routinely processed paraffin-embedded tissue blocks, localized cells possessing these abnormalities of chromosome 3 to both the follicular and marginal zone components of two lymphomas studied in this way.

CONCLUSIONS

Trisomy 3 and alterations involving the q27-29 region of chromosome 3 are implicated in the pathogenesis of de novo marginal zone lymphoma. Their presence in the current cases indicates that they may also be responsible for marginal zone differentiation in follicular lymphoma when cells harbouring these genetic alterations are exposed to the appropriate microenvironment. Our findings are consistent with follicular lymphoma with marginal zone differentiation as a high-risk variant of follicular lymphoma.

Microsatellite instability and hMLH1 promoter hypermethylation in Richter's transformation of chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is an indolent B cell non-Hodgkin lymphoma (NHL) that may transform into diffuse large B cell lymphoma (DLBL). This transformation is referred to as Richter's syndrome or transformation. To analyze whether microsatellite instability (MSI) and DNA mismatch repair defects are associated with Richter's transformation, we have performed microsatellite analysis, mutational analysis of hMLH1 and hMSH2 genes and methylation status analysis of CpG island of the hMLH1 promoter on serial biopsy specimens from 19 patients with CLL. Ten cases of CLL showed no histologic alteration in the second biopsy, and nine cases of CLL underwent morphologic transformation to DLBL in the second biopsy. Using eight microsatellite loci, high level of MSI was associated with Richter's transformation in four cases of CLL, but none of the CLLs displayed this level of MSI without transformation. Mutations of the hMLH1 or hMSH2 genes were not detected in any of the lymphoma samples. In five cases of Richter's transformation the hMLH1 promoter was hypermethylated in both CLL and DLBL samples. Hypermethylation of the hMLH1 promoter associated with high-level of MSI in four cases, and low-level of MSI in one case. These results suggest that in certain cases of Richter's transformation the DNA mismatch-repair defect-initiated genetic instability may play a role in tumor progression.

Genetic analysis of de novo CD5+ diffuse large B-cell lymphomas suggests an origin from a somatically mutated CD5+ progenitor B cell

CD5(+) diffuse large B-cell lymphomas (DLBLs) have recently been described as a particular subgroup of DLBLs. Classical banding and interphase cytogenetic analyses targeting ATM, TP53, and P16(INK4a) genes and the D13S25 locus from 13 CD5(+) DLBLs were compared with 55 CD5(-) DLBLs. Additionally, analysis of somatic mutations of the immunoglobulin heavy chain variable region (IgVH) genes were performed in CD5(+) DLBLs. CD5(+) DLBLs were somatically mutated (7 of 8 cases) and were negative for t(11;14)(q13;q32) and t(14;18)(q32;q21), whereas t(3;14)(q27;q32) was found in only one tumor. Trisomy 3 and gains on chromosomes 16/16p and 18/18q were significantly overrepresented in CD5(+) DLBLs. No ATM deletions were detected. The prevalence of deletions at the D13S25 locus was significantly higher in CD5(+) DLBLs (4 of 12 [33%]) compared with CD5(-) DLBLs (4 of 42 [10%]), as were p16(INK4a) deletions (33% versus 8%). On the basis of these findings, CD5(+) DLBLs are likely to arise from the same progenitor cell as the mutated variant of CD5(+) lymphocytic lymphoma/B-cell chronic lymphocytic leukemia (B-CLL).

Reliability of lymphoma classification in bone marrow trephines

The aim of this study was to test and establish the accuracy and reliability of lymphoma classification in bone marrow trephines according to the new World Health Organization (WHO) classification by considering predominantly the morphology and immunophenotype. Therefore, we retrospectively compared lymphoma diagnoses, rendered exclusively on bone marrow trephines without knowledge of lymph node diagnosis in 124 patients, with the results of the reference centres that had reviewed lymph node (n = 90) or extranodal biopsies (n = 34). The overall concordance rate was higher than 85% and 91%, respectively, when patients with discordant malignancy grades were excluded. The concordance rate for low-grade B-cell lymphomas was 93% and for high-grade B-cell lymphomas 84%. The main reasons for discordant diagnoses were divergent immunophenotypes among low-grade B-cell lymphomas (6 out of 81, i.e. 7.4%) and discrepant malignancy grades within high-grade B-cell lymphomas (6 out of 31, i.e. 19.4%). No relationship between discordant diagnoses and chemotherapy given during the course of the disease with the site of biopsy (i.e. lymph nodes, extranodal sites) was noted. We conclude from our results that bone marrow trephines are a reliable tool, not only for establishing bone marrow infiltration, but also for the subtyping of lymphomas.