Cytogenetic study of two cases with lymphoma of mucosa-associated lymphoid tissue

Recent Advances in the Genetic of MALT Lymphomas

Simple Summary

Mucosa-associated lymphoid tissue (MALT) lymphoma is the most common subtype of marginal zone lymphomas. These B-cell neoplasms may arise from many organs and usually have an indolent behavior. Recurrent chromosomal translocations and cytogenetic alterations are well characterized, some of them being associated to specific sites. Through next-generation sequencing technologies, the mutational landscape of MALT lymphomas has been explored and available data to date show that there are considerable variations in the incidence and spectrum of mutations among MALT lymphoma of different sites. Interestingly, most of these mutations affect several common pathways and some of them are potentially targetable. Gene expression profile and epigenetic studies have also added new information, potentially useful for diagnosis and treatment. This article provides a comprehensive review of the genetic landscape in MALT lymphomas.

Abstract

Mucosa-associated lymphoid tissue (MALT) lymphomas are a diverse group of lymphoid neoplasms with B-cell origin, occurring in adult patients and usually having an indolent clinical behavior. These lymphomas may arise in different anatomic locations, sharing many clinicopathological characteristics, but also having substantial variances in the aetiology and genetic alterations. Chromosomal translocations are recurrent in MALT lymphomas with different prevalence among different sites, being the 4 most common: t(11;18)(q21;q21), t(1;14)(p22;q32), t(14;18)(q32;q21), and t(3;14)(p14.1;q32). Several chromosomal numerical abnormalities have also been described, but probably represent secondary genetic events. The mutational landscape of MALT lymphomas is wide, and the most frequent mutations are: TNFAIP3, CREBBP, KMT2C, TET2, SPEN, KMT2D, LRP1B, PRDM1, EP300, TNFRSF14, NOTCH1/NOTCH2, and B2M, but many other genes may be involved. Similar to chromosomal translocations, certain mutations are enriched in specific lymphoma types. In the same line, variation in immunoglobulin gene usage is recognized among MALT lymphoma of different anatomic locations. In the last decade, several studies have analyzed the role of microRNA, transcriptomics and epigenetic alterations, further improving our knowledge about the pathogenic mechanisms in MALT lymphoma development. All these advances open the possibility of targeted directed treatment and push forward the concept of precision medicine in MALT lymphomas.

A20 deletion is associated with copy number gain at the TNFA/B/C locus and occurs preferentially in translocation-negative MALT lymphoma of the ocular adnexa and salivary glands

The genetic basis of MALT lymphoma is largely unknown. Characteristic chromosomal translocations are frequently associated with gastric and pulmonary cases, but are rare at other sites. We compared the genetic profiles of 33 ocular adnexal and 25 pulmonary MALT lymphomas by 1 Mb array-comparative genomic hybridization (CGH) and revealed recurrent 6q23 losses and 6p21.2-6p22.1 gains exclusive to ocular cases. High-resolution chromosome 6 tile-path array-CGH identified NF-kappaB inhibitor A20 as the target of 6q23.3 deletion and TNFA/B/C locus as a putative target of 6p21.2-22.1 gain. Interphase fluorescence in situ hybridization showed that A20 deletion occurred in MALT lymphoma of the ocular adnexa (8/42=19%), salivary gland (2/24=8%), thyroid (1/9=11%) and liver (1/2), but not in the lung (26), stomach (45) and skin (13). Homozygous deletion was observed in three cases. A20 deletion and TNFA/B/C gain were significantly associated (p<0.001) and exclusively found in cases without characteristic translocation. In ocular cases, A20 deletion was associated with concurrent involvement of different adnexal tissues or extraocular sites at diagnosis (p=0.007), a higher proportion of relapse (67% versus 37%) and a shorter relapse-free survival (p=0.033). A20 deletion and gain at TNFA/B/C locus may thus play an important role in the development of translocation-negative MALT lymphoma.

Typical genomic imbalances in primary MALT lymphoma of the orbit

Primary orbital non-Hodgkin lymphoma is a mucosa-associated lymphoid tissue (MALT)-type extranodal marginal zone lymphoma. Little information is available on its genome as conventional cytogenetics is limited by scarce biopsy material, while fluorescence in situ hybridization (FISH) explores only selected regions. Comparative genomic hybridization (CGH) performs full genomic analysis and is applicable to different sources of DNA, such as fresh and frozen cells, as well as paraffin-embedded tissues. In this study, CGH was used to analyse primary MALT lymphoma of the orbit. Aneuploidy was identified in six of the ten cases studied. Gains (19) were more frequent than losses (5). The most frequent duplications involved chromosome 3 (common region at 3q24-qter), as expected in marginal zone lymphoma, and chromosome 6 (common region at 6p21.1-21.3), which is typical of an orbital location. Other chromosome gains were found at 1p, 7, 8q, 9q, 12, 13, 17, 18, 19, 22, and X. Losses were located at 1q, 6q, 9q, 11q, and 13q. Two cases showed isolated duplications of chromosome 6p or 9q. Isolated imbalances were found only in tumours affecting the conjunctiva. Complex aneuploidies were observed in lymphoma of the retro-orbital tissue. In summary, CGH in orbital MALT lymphoma provided new insights into typical genomic imbalances and underlying pathogenetic mechanisms.

Gastric marginal zone B-cell lymphomas of MALT type develop along 2 distinct pathogenetic pathways

Low-grade marginal zone B-cell lymphoma of mucosa-associated lymphoid tissue (MALT) type can transform into high-grade diffuse large B-cell lymphoma (DLBCL). Up to 60% of the MALT lymphomas contain the recently described t(11;18). However, this translocation has not been detected in any DLBCL so far. To elucidate the pathogenesis of these tumors, microsatellite screening of 24 gastric MALT lymphomas was performed and the results were compared with aberrations detected in a previous study on gastric DLBCL. The most frequent aberration, found in 21% of the MALT lymphomas that were exclusively t(11;18)-negative cases, was amplification of the 3q26.2-27 region (harboring the locus of the BCL6 gene). Allelic imbalances in regions 3q26.2-27, 6q23.3-25, 7q31, 11q23-24, and 18q21 were shared by both MALT lymphoma and DLBCL. Loss of heterozygosity in regions 5q21 (APC gene locus), 9p21 (INK4A/ARF), 13q14 (RB), and 17p13 (p53) and allelic imbalances in 2p16, 6p23, and 12p12-13 occurred exclusively in DLBCL. Only one of 10 t(11;18)-positive MALT lymphomas showed an additional clonal abnormality. These tumors thus display features of a clonal proliferation characterized by the presence of the t(11;18). However, they only rarely display secondary aberrations and do not seem to transform into DLBCL. In contrast, t(11;18)-negative MALT lymphomas show numerous allelic imbalances--some of them identical with aberrations seen in DLBCL--suggesting that this group is the source of tumors eventually transforming into high-grade DLBCL.

Molecular aspects of B-cell lymphomas of the gastrointestinal tract

The B-cell lymphomas of the gastrointestinal (GI) tract have represented a field of extensive research ever since a close association was shown with such chronic inflammatory processes as Helicobacter pylori infection. Evidence suggested that the mucosa-associated lymphoid tissue induced by inflammation and autoimmune processes is the environment that gives rise to the small-cell lymphomas of the GI tract (eg, extranodal marginal zone B-cell lymphoma according to Revised European-American Classification of Lymphoid Neoplasms and the World Health Organization Classification of Neoplastic Diseases of the Hematopoietic and Lymphoid Tissue). The small B-cell lymphoma may then progress to highly malignant variants. The B-cell lymphomas of the GI tract may present a stepwise model for lymphomagenesis and progression. This review covers molecular biology and molecular cytogenetic aspects that lead to new insights into the biology of GI lymphomas and potential prognostic factors.

Malignant tumors of the stomach. Gastric mucosa-associated lymphoid tissue lymphoma and Helicobacter pylori

With the help of many clinical studies, the diagnosis and therapy of gastric MALT lymphoma have evolved. Major progress has been seen in this area, including improvement of biopsy diagnosis, better histologic classification, new information concerning pathogenesis, and, especially, the start of a revolution in the treatment of low-grade gastric MALT lymphomas by eradicating H. pylori. About 12 clinical studies with almost 400 patients and case reports have shown that cure of H. pylori infection is associated with complete remission in approximately 80% of patients with low-grade MALT lymphoma in an early clinical stage. To establish H. pylori eradication as the primary choice in low-grade gastric MALT lymphoma further, it is necessary to select patients before therapy who are most likely to benefit from this single treatment modality. An excellent histologic workup of obtained biopsy specimens and comprehensive clinical staging are necessary. Because of the supposition that H. pylori-related growth support may play a role only in the early stages of low-grade gastric MALT lymphoma, the importance of determining the depth of lymphoma infiltration in the gastric wall is evident. Examinations by endosonographic ultrasonography have been shown to be the most reliable method to differentiate the layers of the gastric wall and to determine the infiltration depth of lymphomas. Eradication of H. pylori has to be considered as a first-line and single treatment modality in patients with low-grade gastric MALT lymphoma in clinical stage EI1. As a therapy with fewer side effects than radiation, surgery, or chemotherapy and as a stomach-conserving treatment, eradication of H. pylori in patients with low-grade gastric MALT lymphoma should be the treatment of the choice within clinical trials because there are no long-term results available thus far. Besides pretreatment patient selection, careful follow-up with endoscopy, biopsies, and clinical staging including endoscopic ultrasonography is necessary. A 5- to 10-year follow-up is necessary before the definitive value of H. pylori eradication can be established, but long-term results are excellent thus far. There are many questions to be addressed: What are the exact mechanisms that lead to the malignant transformation of a reactive infiltrate? Why do approximately 20% of low-grade MALT lymphomas not regress after H. pylori eradication? Is there a molecular-genetic or immunologic point of no return? What is the biologic significance of the immunoglobulin rearrangement detected with PCR? What will be the 5- and 10-year relapse-free survival rates of patients suffering from low-grade MALT lymphoma treated with H. pylori eradication alone as first and only treatment? The wave of new data each year about the role of H. pylori in gastric MALT lymphoma may help many of these questions to be answered.

Gastric MALT lymphoma and its relationship to Helicobacter pylori infection: management and pathogenesis of the disease

Chronic Helicobacter pylori infection is strongly associated with the development of primary gastric B cell lymphoma of MALT-type. Therapeutic decisions in primary gastric MALT lymphomas, e.g., the choice for gastric surgery or stomach-conserving treatments in the form of radio-, chemo-, or eradication therapy, should be based on an accurate histopathological diagnosis, grading and clinical staging. Primary gastric low-grade MALT-NHLs in an early clinical stage associated with H. pylori infection were shown to respond with complete remission in approximately 77% of cases upon successful cure of the infection as only treatment modality. The effect of curing H. pylori infection on the course of a high-grade gastric MALT lymphoma is largely uncertain but preliminary results indicate a possible benefit for patients with high-grade MALT lymphoma upon eradication therapy. Concerning the pathogenetic mechanisms of lymphomagenesis, there are many questions to be addressed in the near future. In general, it is still unclear what the exact mechanisms are which lead to the malignant transformation of a reactive infiltrate. Is there a molecular-genetic or immunological point of no return? What is the biological significance of the immunoglobulin rearrangement detected with PCR? The wave of new data each year about the role of H. pylori in gastric MALT lymphoma might help that many of these questions addressed above might be answered within the next years.

Genetic abnormalities in marginal zone B-cell lymphoma

Marginal zone B-cell lymphoma (MZBCL) including extranodal mucosa-associated lymphoid tissue (MALT)-type lymphoma, nodal, and splenic MZBCL represents a distinct subtype of B-non-Hodgkin's lymphoma. Recently, important progress in the elucidation of the genetic mechanisms underlying the pathogenesis and disease progression of these lymphomas has been made. The API2 gene, an inhibitor of apoptosis, and the novel MLT gene have been found to be altered by the t(11;18)(q21;21), which represents the most frequent structural chromosomal abnormality in extranodal low-grade MALT lymphoma. Another gene involved in the regulation of apoptosis, the BCL10 gene, has been cloned from a MALT lymphoma cytogenetically characterized by the t(1;14)(p22;q32). Along the same lines, inactivating mutations of the proapoptotic FAS gene have been detected in a relatively high proportion of extranodal MZBCLs. Considering these data and the fact that at least some MALT lymphomas show low levels of apoptosis and seem to escape from FAS-mediated apoptosis one may speculate that abrogation of apoptosis constitutes a central pathogenetic mechanism in the development of these lymphomas. The pathogenetic role of trisomy 3, the most frequent numerical chromosomal change of MZBCL, is not known. The minimal overrepresented region has been delineated to 3q21-23 and 3q25-29 using comparative genomic hybridization. The BCL6 proto-oncogene, located on 3q27, which is rearranged in some MZBCL and a high proportion of large cell B-cell lymphomas with extranodal localization, represents one of the candidate genes residing in these critical regions.

Genetic imbalances in primary gastric diffuse large B-cell lymphomas: comparison of comparative genomic hybridization, microsatellite, and cytogenetic analysis

Extranodal malignant non-Hodgkin's lymphomas account for about 40% of lymphoid neoplasms, but few data are available concerning the genetic background of primary gastric diffuse large B-cell lymphoma (DLBCL). A study was performed of 27 primary gastric DLBCLs and 5 gastric DLBCLs with a concomitant low grade component of mucosa-associated lymphoid tissue-type lymphoma using comparative genomic hybridization (CGH), microsatellite studies, classic cytogenetics, and fluorescence in situ hybridization (FISH) to search for specific genetic aberrations. The most frequent aberrations were losses of material on chromosome 6q and gains of parts of chromosome 3. In three cases, a total of six high level DNA amplifications were detected, with five of them involving chromosomal regions not having been reported before in gastric DLBCL. A high overall concordance of 91.4% between microsatellite analysis and CGH was observed using DNA extracted from the same tissue block. The concordance achieved using DNA from different tissue blocks of the same patient was 85%. Microsatellite studies, CGH, FISH, and classic cytogenetics represent complementary techniques that facilitate a comprehensive view of genetic alterations in malignancies such as primary gastric DLBCL.

Sjögren's syndrome and MALT lymphomas of salivary glands: a DNA-cytometric and interphase-cytogenetic study

Few and conflicting cytogenetic data are available concerning the chromosomal constitution of (mainly gastric) extranodal marginal zone B-cell non-Hodgkin's lymphoma arising from mucosa-associated lymphoid tissue (MALT)-type lymphoma. The majority of salivary gland MALT lymphomas are thought to develop from longstanding Sjögren's syndrome/benign lymphoepithelial lesion (BLEL). We tried to achieve a better comprehension of related cytogenetic alterations by comparing DNA-ploidy and numerical chromosomal (#) aberrations, assessed by different techniques of DNA cytometry (image cytometry) and interphase cytogenetics using nonradiographic in situ hybridization (centromere specific probes for #3, 7, 12, 18) on 12 cases of BLEL, 13 low-grade MALT lymphomas (LG-MALT-L) and 4 high-grade MALT lymphomas (HG-MALT-L) of salivary gland. Both techniques were applied on tissue sections preferentially, enabling a reliable measurement of histomorphologically identified areas. No case of BLEL showed cytogenetic abnormalities. Three of 4 HG- and 2 of 13 LG-MALT-L exhibited complex chromosomal gains in nonisotopic in situ hybridization, which were reflected by DNA nondiploidy in image cytometry. In 6 of 13 LG- and lof 4 HG-MALT-L, one or two numerical chromosomal aberrations were demonstrated by nonisotopic in situ hybridization, which could not be resolved by image cytometry. In the 11 DNA-diploid LG-MALT-L, trisomies 18, 3, and 12 were found in 36, 12, and 9%, respectively. In conclusion, comparing BLEL, which showed no chromosomal aberrations, with LG- and HG-MALT-L, an increase in frequency and number of numerical aberrations and DNA nondiploidy was seen. Peritetraploid DNA nondiploidy might be characteristic for HG-MALT-L of salivary gland as it is a rare finding in MALT lymphomas of other sites. It is unclear whether the documented chromosomal aberrations in LG-MALT-L, especially increased rate of trisomy 18, indicate a pathogenic impact or merely reflect genetic instability.

Expression of cdc2 and cyclin B1 in Helicobacter pylori-associated gastric MALT and MALT lymphoma : relationship to cell death, proliferation, and transformation

Mucosa-associated lymphoid tissue (MALT) may accumulate within gastric mucosa as a result of long standing Helicobacter pylori infection, and this acquired MALT may eventually develop into low-grade B-cell MALT lymphoma. To determine the possible association of cell cycle regulatory proteins and apoptotic cell death in the transformation of H. pylori gastritis to MALT lymphoma, the extent of cell proliferation, cell viability, expression of Cdc2/Cdk1 and cyclin B in gastric mucosal from patients with H. pylori-positive chronic gastritis (n = 7), MALT (n = 12), or MALT lymphoma (n = 12) were undertaken. Control tissue was obtained from H. pylori- negative patients (n = 5). Proliferating cell nuclear antigen (PCNA), Cdc2, and cyclin B1 were examined in paraffin embedded tissue by immunohistochemistry, while the apoptotic index (AI) was determined using the TUNEL assay. H&E staining for histology and modified Giemsa staining for the detection of H. pylori was conducted simultaneously. When compared to chronic gastritis tissue, those with MALT or MALT lymphoma had an increase in PCNA labeling index of 3.3- and 2.7-fold, while that for Cdc2/Cdk1 increased 2.3- and 3.1-fold, respectively. cyclin B1 labeling was 1.9 and 3.0 fold, while the AI was 3.4- and 1.4-fold higher in MALT and MALT lymphoma tissue, respectively, in the same comparison. On the other hand, the AI index of MALT lymphoma was 2. 5-fold lower than that for MALT tissues. The labeling scores for Cdc2/Cdk1 and cyclin B1 were significantly higher in the germinal center when compared to the mantle and marginal zones of MALT tissues. Using chi(2) and Pearson/Spearman's rho correlation coefficient with regression analyses, there was an inverse correlation between the AI and Cdc2/Cdk1 or cyclin B1 in MALT and MALT lymphoma tissues. There was no correlation between AI and PCNA labeling in any of the tissues. These results suggest that Cdc2/Cdk1 and cyclin B1 expression may be actively associated in the modulation of cellular death by apoptosis, as well as cellular proliferation and transformation during the evolution of H. pylori-associated gastritis to MALT lymphoma. Subclassification of high labeling score (>/=40) for Cdc2/Cdk1 and cyclin B1 and low labeling index (<0.6) for apoptotic cells in H. pylori-associated MALT may help in identifying a population of patients with an increased risk of developing MALT lymphoma.

Chromosomal aberrations in lymphomas of the gastrointestinal tract

B-cell lymphomas of the gastrointestinal (GI) tract have represented a field of extensive research ever since a close association was shown with chronic inflammatory processes such as Helicobacter pylori infection. Much evidence has accumulated to suggest that the mucosa-associated lymphoid tissue (MALT) induced by inflammation and autoimmune processes is the environment which gives rise to the small cell lymphomas of the GI tract (e.g. extranodal marginal B-cell lymphoma according to REAL). The small B-cell lymphoma may then progress to the large cell variants. Hence, B-cell lymphomas of the GI tract may present a model for lymphomagenesis and progression. In this review, recent cytogenetic data are discussed which yield new insights into the biology of gastrointestinal lymphomas.

Microsatellite instability in gastric MALT lymphomas and other associated neoplasms

BACKGROUND

Microsatellite instability (MSI), caused by a reduced efficacy of the DNA mismatch repair (MMR) machinery, represents a type of genomic instability frequently detected in HNPCC spectrum cancers and in a subset of sporadic carcinomas. The involvement of MSI in the pathogenesis of gastric lymphoma of mucosa-associated lymphoid tissue (MALT) has never been conclusively investigated. In this study, we tested the presence of MSI in tumor samples of patients harboring both MALT lymphomas and other types of malignancies.

MATERIALS AND METHODS

We examined 10 microsatellite loci (D3S11, D3S1261, D3S1265, D6S262, D6S193, BAT-26, BAT-25, D17S250, APC, D2S123) out of a total of 34 primary tumors from 14 patients with MALT lymphomas and one or more additional neoplasms. The patients' MSI results were also tested for an association with a positive family history of cancer.

RESULTS

MSI, defined by the presence of microsatellite alterations in more than 40% of the examined loci, was scored negative in all tumors studied, and pedigree analysis failed to identify any condition of familial cancer among the patients examined.

CONCLUSIONS

The present study suggests that defects in DNA mismatch repair do not contribute significantly to the molecular pathogenesis of MALT lymphomas and associated neoplasms.

The Apoptosis Inhibitor Gene API2 and a Novel 18q Gene,MLT, Are Recurrently Rearranged in the t(11;18)(q21;q21) Associated With Mucosa-Associated Lymphoid Tissue Lymphomas

Marginal zone cell lymphomas of the mucosa-associated lymphoid tissue (MALT) are the most common subtype of lymphoma arising at extranodal sites. The t(11;18)(q21;q21) appears to be the key genetic lesion and is found in approximately 50% of cytogenetically abnormal low-grade MALT lymphomas. We show that the API2 gene, encoding an inhibitor of apoptosis also known as c-IAP2, HIAP1, andMIHC, and a novel gene on 18q21 characterized by several Ig-like C2-type domains, named MLT, are recurrently rearranged in the t(11;18). In both MALT lymphomas analyzed, the breakpoint inAPI2 occurred in the intron separating the exons coding respectively for the baculovirus IAP repeat domains and the caspase recruitment domain. The breakpoints within MLT differed but the open reading frame was conserved in both cases. In one case, the translocation was accompanied by a cryptic deletion involving the 3′ part of API2. As a result, the reciprocal transcript was not present, strongly suggesting that the API2-MLT fusion is involved in the oncogenesis of MALT lymphoma.

Trisomy 3 in gastric lymphomas of extranodal marginal zone B-cell (mucosa-associated lymphoid tissue) origin demonstrated by FISH in intact paraffin tissue sections

Some reports have indicated that trisomy 3 represents a characteristic chromosomal abnormality found in lymphomas arising in mucosa-associated lymphoid tissues (MALT)/extranodal marginal zone B-cells (MZBC). Traditional cytogenetic analysis of metaphase preparations is cumbersome and not always possible, especially in those situations in which the diagnosis in not suspected before a biopsy. Our aim is to use a relatively simple method to evaluate trisomy 3 in paraffin-embedded, formalin-fixed tissue, using fluorescence in situ hybridization (FISH) on intact tissue sections. Formalin-fixed, paraffin-embedded archival tissues from 30 cases (27 lymphoma and 3 chronic gastritis cases) were hybridized with a chromosome 3 specific alpha-satellite probe (ONCOR, Gaithersburg, MD). Three of four cases of gastric MZBC/MALT lymphoma revealed trisomy 3. Ten cases of lymphoma of possible or probable MZBC origin were examined, and four revealed trisomy 3. Five of 13 non-MZBC lymphomas revealed trisomy 3. None of the chronic gastritis cases nor normal tonsil cases revealed trisomy 3. Our results, using a different methodological approach, confirm the findings of others that trisomy 3 is an abnormality found in a significant proportion of lymphomas of MZBC origin. Our approach also makes possible interphase cytogenetic analysis (by FISH) of routinely processed formalin-fixed, paraffin-embedded tissues, without the need to disaggregate cells. It thus may facilitate genetic analysis on specimens previously deemed unsuitable for such analysis, particularly when tissue quantity is limited.

The Apoptosis Inhibitor Gene API2 and a Novel 18q Gene,MLT, Are Recurrently Rearranged in the t(11;18)(q21;q21) Associated With Mucosa-Associated Lymphoid Tissue Lymphomas

Marginal zone cell lymphomas of the mucosa-associated lymphoid tissue (MALT) are the most common subtype of lymphoma arising at extranodal sites. The t(11;18)(q21;q21) appears to be the key genetic lesion and is found in approximately 50% of cytogenetically abnormal low-grade MALT lymphomas. We show that the API2 gene, encoding an inhibitor of apoptosis also known as c-IAP2, HIAP1, andMIHC, and a novel gene on 18q21 characterized by several Ig-like C2-type domains, named MLT, are recurrently rearranged in the t(11;18). In both MALT lymphomas analyzed, the breakpoint inAPI2 occurred in the intron separating the exons coding respectively for the baculovirus IAP repeat domains and the caspase recruitment domain. The breakpoints within MLT differed but the open reading frame was conserved in both cases. In one case, the translocation was accompanied by a cryptic deletion involving the 3′ part of API2. As a result, the reciprocal transcript was not present, strongly suggesting that the API2-MLT fusion is involved in the oncogenesis of MALT lymphoma.

Cytogenetic changes in the progression of lymphoma

The study of chromosomal changes related to tumor progression in NHL is complicated by the various histologic classification systems and the lack of large serial studies comparing abnormalities at different disease stages. The T-cell lymphomas frequently involve rearrangements of the T-cell receptors and tumor progression is marked by a change from single cell aberrations and polyclonality in low grade disease to monoclonal formation, complex clones, polyploidy, and abnormalities of 1p, 6q, 7, and 13 in high grade T-NHL. In B-cell NHL, specific translocations and oncogene rearrangements are associated with specific NHL subtypes de novo; many of these translocations involve immunoglobulin genes, such as t(14;18) in follicular lymphoma, t(11;14) in MCL, t(3;14) in DLLC, and t(8;14) in Burkitt's lymphoma. Tumor progression is associated with secondary abnormalities which are generally not confined to a particular NHL subtype. Some abnormalities, such as those involving chromosomes 1, 6, and 17, >4-6 clonal markers/cell, and rearrangements of c-MYC and TP53, have prognostic significance while others, such as trisomies 7, 12, 18, and X, are associated with tumor progression but their influence on overall survival is uncertain.

Trisomy 3 is not a common feature in malignant lymphomas of mucosa-associated lymphoid tissue type

The genetic background of extranodal marginal zone B-cell non-Hodgkin's lymphoma (NHL) of mucosa-associated lymphoid tissue (MALT) type is poorly understood. In contrast to most entities of primary nodal lymphomas, few cytogenetic data are available, and gene rearrangements frequently encountered in and highly characteristic of certain entities of systemic NHL are absent in this type of lymphoma. Recently, it was suggested that MALT-type NHLs are associated with certain numerical chromosome aberrations and especially with trisomy 3. We performed an extensive study using a sensitive double (bicolor) fluorescence in situ hybridization technique for the analysis of trisomies for chromosomes 3, 7, 12, and 18 in 60 samples of low-grade and 45 high-grade MALT-type tumors. In the low-grade cases, trisomy 3 was found in a frequency of only 20%. High-grade lymphomas of MALT type were associated with trisomies 3, 7, 12, and 18 in 36, 20, 18, and 13% of the cases, respectively. Whereas no difference was encountered for trisomy 3 in primary and secondary/simultaneous high-grade lymphomas, +7 and +12 were associated with primary lymphomas, and a +18 was predominantly found in secondary/simultaneous high-grade NHL. These results challenge earlier reports describing a high frequency of +3 in low-grade MALT-type NHL and indicate a possibly different genetic evolution pattern of primary and secondary/simultaneous high-grade lymphomas of primary mucosal origin.

Gastric low-grade mucosa-associated lymphoid tissue lymphomas: their histogenesis and high-grade transformation

Gastric low-grade mucosa-associated lymphoid tissue (MALT) lymphoma is a unique disease. A vast majority of lymphoma cells are centrocyte-like cells or resemble monocytoid B cells, and occasionally show plasmacytic differentiation. Immunophenotypical and immunogenotypical examinations have indicated that they are in the differentiation stage of memory B cells, whose normal counterparts are marginal zone lymphocytes or monocytoid B cells in the lymphoid tissues. It arises from chronic gastritis closely associated with Helicobacter pylori (H. pylori) infection. Mucosa-associated lymphoid tissue lymphomas of other organs are also based on acquired MALT associated with chronic inflammation or autoimmune diseases. Interestingly, the majority of gastric low-grade MALT lymphomas regress by the eradication of H. pylori. The lymphoma cells, however, are not derived from B cells reacting with H. pylori itself but from autoreactive B cells. Although the mechanism of their oncogenesis has not been clarified, previous data suggest that autoreactive B cells proliferate in response to H. pylori-specific T cells, presumably with some cytokines. The genetic instability of such B cells then induces chromosomal abnormalities including trisomy 3 and/or other genetic changes. These B cells have the ability of autonomic proliferation and, even so, they might be sensitive to T cell stimuli. Low-grade gastric lymphomas occasionally progress to high-grade malignancy. The high-grade component of MALT lymphomas are composed of large-sized lymphoma cells that are morphologically indistinguishable from nodal large B cell lymphomas. This high-grade transformation is associated with p53 abnormalities or Bcl-6 overexpression. Gastric MALT lymphoma may provide a useful model in understanding multistep lymphomagenesis.

Multiple polypoid lesions of primary mucosa-associated lymphoid-tissue lymphoma of colon

AIMS

This study was focused on unusual cases of mucosa-associated lymphoid tissue (MALT) lymphoma presenting with multiple polypoid lesions of the colon and rectum with a special reference to the differential diagnosis of mantle cell lymphoma.

METHODS AND RESULTS

The lesions of these five cases grossly showed a segmental distribution of nodular protrusions in three patients and of innumerable small polyps in two. These patterns of involvement simulated those of multiple lymphomatous polyposis, known as the gastrointestinal presentation of mantle cell lymphoma (MCL), and caused a differential diagnostic problem between MALT lymphoma and MCL, which have different prognostic and therapeutic implications. Their histological features are almost indistinguishable from each other, especially in the small biopsy specimens via endoscope. The most important procedure for their differentiation is cyclin D1 immunohistochemistry and its negative reaction provides strong indication of MALT lymphoma. Of interest, one case showed a rare karyotypic abnormality of t(11;18)(q21;q21), which has been reported specifically in MALT lymphoma.

CONCLUSIONS

This study has indicated that the multiple polypoid lesions of the colon occur not only in MCL, but also in MALT lymphoma, making differential diagnosis between the two entities necessary, and cyclin D1 immunohistochemistry is indispensable for distinguishing between them.

Marginal zone B-cell lymphomas including mucosa-associated lymphoid tissue type lymphoma (MALT), monocytoid B-cell lymphoma and splenic marginal zone cell lymphoma and their relation to the reactive marginal zone

The marginal zone of the B follicle represents a well-defined compartment of the B area. Its cellular composition is distinct from that of the follicle centre, from which it also differs in its functional role in the immune response. Several newly identified lymphoma entities, e.g. extranodal MALT type lymphoma, nodal monocytoid B-cell lymphoma and splenic marginal zone B-cell lymphoma, display in common a very peculiar organoid growth pattern reminiscent of the marginal zone. Moreover, their neoplastic components share morphologic and phenotypic similarities to the cellular components of the marginal zone. The clinical characteristics of these various marginal zone cell lymphomas may differ depending of the organ which is involved. Nevertheless, they all share common cytogenetic abnormalities suggesting a common pathogenesis.