No evidence of replication error phenotype in primary gastric lymphoma of mucosa-associated lymphoid tissue

Instability of clonality in gastric lymphoid infiltrates: a study with emphasis on serial biopsies

The evolution of low-grade B-cell mucosa-associated lymphoid-tissue (MALT) lymphoma of the stomach is a multistage process, reflected in the histologic continuum from Helicobacter pylori-chronic gastritis, to low-grade and high-grade lymphoma. Interestingly, in daily gastric biopsy sign-out, the authors observed that some biopsies showed monoclonality on polymerase chain reaction (PCR) even though there were no definite histologic features of malignancy and vice versa. To address the question, the authors studied the endoscopic gastric biopsies at first presentation of 46 patients to examine any clonality differences among various histologic patterns within the spectrum of MALT lymphoma evolution. The gastric biopsies were reviewed histologically and graded according to the Wotherspoon-Isaacson histologic scoring system from grade 0 (normal) to grade 5 (MALT lymphoma). The clonality of cases in each grade was determined by performing nested PCR for immunoglobulin heavy chain (IgH) gene rearrangement using FR2/JH and FR3/JH primer sets. The monoclonality rates among different grades were as follows: grade 2, 6.3% (1 of 16); grade 3, 27.3% (3 of 11); grade 4, 83.3% (5 of 6); grade 5, 69.2% (9 of 13). Statistically significant difference of monoclonality rate is demonstrated in histologic grade 4 versus grades 2 and 3, and grade 5 versus grade 2 (P < 0.05, Fisher exact test). The authors went on to examine the progress of disease by following up the clinical status, histologic changes, and clonality fluctuation of these cases. Four of the 8 patients with monoclonality on PCR, but no definite lymphoma at first presentation later progressed to frank MALT lymphoma. Our study shows that, during the progression to MALT lymphoma, there is an instability of clonality. Clonality can fluctuate between polyclonality, oligoclonality, and monoclonality, none of which defines an irreversible stage for progression to MALT lymphoma. Monoclonality is a risk factor for development of MALT lymphoma. Those cases with dense gastric mucosal lymphoid infiltrate (without definite MALT lymphoma) and monoclonality on PCR need to be closely monitored and Helicobacter infection promptly treated if present. In combination with clinicohistologic examination, PCR can serve as a complementary tool in arriving at a definite diagnosis of MALT lymphoma in cases with borderline histologic features.

p53 expression, K-ras gene mutation and microsatellite instability in gastric B-cell lymphomas

BACKGROUND AND AIMS

Genetic mechanisms involved in the development of gastric B-cell lymphomas remain unclear. The aim of the present study was to clarify the roles of mutations of the p53 and K-ras genes, and microsatellite instability (MSI) in the development of gastric B-cell lymphomas.

METHODS

We investigated p53 immunoreactivity, mutations of the K-ras gene, and MSI in 27 gastric marginal zone B-cell lymphomas of mucosa-associated lymphoid tissue type (MZBCL) and 24 diffuse large B-cell lymphomas (DLBCL). p53 immunoreactivity was examined using a monoclonal antibody, DO-7. Mutation of the K-ras gene was detected by polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) analysis. MSI was examined at five microsatellite loci with a microsatellite assay. Cases were classified as having high-frequency MSI (MSI-H) (>/= 2 loci showing instability), low-frequency MSI (MSI-L) (only one locus showing instability), or as microsatellite stable.

RESULTS

p53 immunoreactivity was detected in 1 of 16 (6%) MZBCL and 8 of 19 (42%) DLBCL. Frequency of p53 immunoreactivity in DLBCL was significantly higher than that in MZBCL (P = 0.018). MSI-H was detected only in 1 of 20 (5%) DLBCL. None of the cases examined showed mutation of the K-ras gene.

CONCLUSIONS

These data suggest that mutations of the p53 gene may play an important role in the development of gastric DLBCL, and that mutations of the K-ras gene and MSI may be involved in little part of the development of gastric B-cell lymphomas.

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.

BCL10 somatic mutations rarely occur in gastric lymphoma: detection of high frequency of polymorphisms in BCL10 coding region

The BCL10 gene, recently isolated due to its involvement in the t(1;14)(p22;q32) of mucosa-associated lymphoid tissue B cell non-Hodgkin lymphoma (MALToma), was shown to have frequent somatic mutations and short deletions within the coding region in MALToma and a variety of other lymphomas and solid tumors. These observations have been recently questioned. In this study, we examined BCL10 gene mutations by direct sequencing of the entire coding region of the BCL10 gene, amplified from paired normal and tumor genomic DNAs, as well as tumor cDNAs, in 23 cases of primary gastric B cell non-Hodgkin lymphomas, comprising of 6 cases of MALToma and 17 cases of diffuse large cell (DLC) lymphoma. Heterozygosity due to three types of known polymorphisms in codon 5 (17.3%), codon 8 (21.7%), and codon 213 (8.6%) were observed in both normal germline DNA and tumor DNAs and tumor cDNAs in individual cases. In one case (4.3%) G/C heterozygosity in codon 8 in normal germline DNA was reduced to homozygosity (LOH) in tumor DNA and cDNA. Mutations inactivating BCL10 gene product function were not found in any of these cases. Moreover, post-transcriptional alterations were not indicated by abnormalities in BCL10 mRNA sequence in tumor cDNAs in these gastric lymphoma cases. Our results show that somatic mutations in the BCL10 gene rarely occur in gastric lymphoma and indicate that this gene is unlikely to be of pathogenetic significance in the majority of gastric lymphomas.

PCR artifacts in LOH and MSI analysis of microdissected tumor cells

Polymerase chain reaction (PCR) analysis to study loss of heterozygosity (LOH) and microsatellite instability (MSI) in tumors is widely used. Microdissection techniques are applied to obtain tumor-specific tissue cells. By microdissection, however, the amount of template DNA extracted may vary considerably and interfere with optimal PCR amplification. To circumvent LOH and MSI misinterpretations due to low DNA input, we have assessed the critical level of DNA input for reliable PCR analysis. PCR analysis was performed by using 18 polymorphic markers (mono-, di-, tri-, and tetranucleotide) on DNA derived from both paraffin-embedded, formalin-fixed, and fresh frozen tumor specimens at template input levels ranging from 0.05 to 25.0 ng. We show a highly significant relation between DNA input and the occurrence of LOH and MSI artifacts. Furthermore, for DNA extracted from paraffin-embedded material, the percentage of LOH artifacts is significantly higher compared with DNA extracted from frozen tissue. For reliable PCR analyses using a mono-, di-, tri-, or tetranucleotide marker, a minimum of 10.0 ng DNA is required when DNA is isolated from formalin-fixed, paraffin-embedded tissue and 5.0 ng when isolated from fresh frozen tissue. HUM PATHOL 31:1414-1419.

The role of microsatellite instability in gastric low- and high-grade lymphoma development

DNA mismatch repair genes and their dysfunction as evidenced by microsatellite instability (MSI) play an important role in the pathogenesis of a variety of tumors, most prominently hereditary nonpolyposis colorectal cancer (HNPCC). However, their role in development of extranodal lymphomas has not been established yet. We therefore evaluated for MSI 25 gastric low-grade marginal-zone B-cell lymphomas of mucosa-associated lymphoid tissue type and 31 gastric high-grade diffuse large B-cell lymphomas (DLBCLs) with 29 and 118 microsatellites, respectively. Compared with HNPCC, the overall level of MSI was much lower with a mean of 2.6% MSI-positive repeats in the DLBCLs; the frequency of MSI showed a tendency to increase with age (P = 0.01), as did MSI variability (P = 0.02). Low-grade mucosa-associated lymphoid tissue lymphomas displayed even less MSI (sevenfold) than DLBCLs (P = 0.009). MSI frequency thus increases with the transition from low- to high-grade disease and with age; it does not seem to initiate lymphomagenesis. Other microsatellites than those typically mutated in HNPCC frequently revealed MSI in these lymphomas, especially dinucleotide repeats on chromosomes 3, 5, and 18. To facilitate rapid screening of lymphomas for MSI and to establish a tool for future MSI frequency comparisons, we recommend to use repeats D3S1261, D3S1530, D5S346, D17S250, D18S474, and DCC.

Mucosa-associated lymphoid tissue lymphomas

Mucosa-associated lymphoid tissue (MALT) lymphoma has attracted attention because its concept has amalgamated the study of etiology and pathogenesis in an intriguing group of lymphomas. MALT lymphomas are a B-cell malignancy with characteristic lymphoepithelial lesions; cells are CD20-positive and CD5- and CD10-negative. The molecular changes observed include trisomy 3, t(11;18), and t(1;14) translocations. They commonly occur in the stomach, orbit, salivary glands, and thyroid. Localized disease is present in 60% to 70% of patients. Involvement of multiple extranodal sites has been observed at presentation or during the course of disease. Lymphocyte homing has been implicated in gastrointestinal MALT and may be involved in other MALT lymphomas. Local therapy, either through surgery or radiotherapy, is curative in a high proportion of patients. MALT lymphomas respond to chemotherapy, but there is no evidence that cure can be achieved, although prolonged survival is common. Long-term follow-up is essential for study of the outcomes in this disease.

Microsatellite instability and k-ras, p53 mutations in thyroid lymphoma

Patho-epidemiological studies showed that thyroid lymphoma (TL) arises in inflammatory lesions of chronic lymphocytic thyroiditis (CLTH). Replication error (RER) is found in inflammatory lesions and associated cancer, suggesting that chronic inflammation could be a risk factor for neoplastic development through causing RER. To clarify whether RER is involved in the pathogenesis of TL, we examined the microsatellite instability (MSI) in 9 cases with CLTH and 19 with TL, including 10 diffuse large B-cell lymphoma (DLBL), 4 follicle center cell lymphoma, 3 marginal zone B-cell lymphoma of extranodal (MALT) type, and 2 lymphoplasmacytic type. Sixteen distinct microsatellite repeats were analyzed. Mutations of p53 and k-ras genes were also examined. When alterations at 2 or more microsatellite loci were judged as positive, only 5 DLBL cases exhibited MSI. The frequency of MSI in DLBL was significantly higher than that in other types of TL and CLTH (P < 0.05). Four of 19 cases (21.1%) showed point mutation of the k-ras gene. The k-ras mutations occurred in the cases with DLBL with RER, and four of five cases with RER had a k-ras mutation, indicating a close association between RER and k-ras mutation. p53 mutations were not found in the CLTH. Two of 19 TL cases showed mutations of p53 gene. There was no significant association between RER and p53 mutation. These findings indicate that genomic instability contributes to the progression of TL from low grade to high grade, but not to the development of low grade lymphoma in CLTH lesions.

Molecular genetics of extranodal marginal zone (MALT-type) B-cell lymphoma

Mucosa-associated lymphoid tissue lymphoma is now classified as extranodal marginal zone B-cell lymphoma. We reviewed the current literature on the biological and genetic mechanisms that lead to the development and progression of this unusual lymphoma. Particular attention was given to the clinical and biological significance of the immunoglobulin genes rearrangement, that has been proposed and widely used both diagnostically and as a tool to monitor the response to antibiotic treatment.

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.

Gastric MALT lymphoma: from concept to cure

Gastric MALT lymphomas are clinically and histologically quite distinct from comparable low-grade B-cell lymphomas of lymph nodes. Their histology suggests that immunological mechanisms might be operative in their growth. Given that there is normally no lymphoid tissue in gastric mucosa and that Helicobacter pylori (H. pylori), the only common bacterial antigen in the stomach, results in the accumulation of gastric MALT, the possibility that this organism is implicated in the pathogenesis of gastric lymphoma has been extensively investigated. It appears that most, but not necessarily all, gastric MALT lymphomas arise in MALT acquired in response to H. pylori infection and develop by stepwise accumulation of genetic abnormalities. Early molecular events in the evolution of gastric MALT lymphoma from 'acquired' MALT include trisomy 3, t(11;18)(q21;q21), genetic damage leading to genetic instability, as indicated by the so-called replication error repair (RER) phenotype, and both p53 and c-myc mutations. At this stage in their development, the growth of the lymphomas is driven by contact between the neoplastic B cells and H. pylori specific intra-tumoral T cells. Eradication of H. pylori causes the tumour to enter a latent phase resulting in clinical regression. Later events, such as t(1;14)(p22;q32), appear to be linked to a capacity for autonomous growth, loss of sensitivity to H. pylori and dissemination of the lymphoma beyond the stomach and gastric lymph nodes. Cloning of the breakpoint in t(1;14) has allowed the identification of a new tumour suppresser gene, bc110. High grade transformation of MALT lymphoma has been associated with p53 inactivation, deletions of p16 and t(8;14).