Primary Gastric Lymphoma

Primary gastrointestinal tract lymphoma: diagnosis and management of common neoplasms

Primary gastrointestinal lymphoma represents the most common location of extranodal lymphoma. With the bulk of disease manifesting within the gastrointestinal tract and contiguous lymph nodes, many of the lymphomas occurring in the peripheral lymph nodes can also present with primary gastrointestinal tract involvement. Molecular biology has recently enabled significant progress in the diagnosis and management of primary gastrointestinal lymphoma. Herein, we will discuss the major lymphomas affecting the bowel and highlight their key morphological, immunophenotypical and molecular diagnostic attributes. Similarly, in keeping with recent therapeutic advances, we will briefly discuss some important treatment considerations. Thus, this review is intended to offer clinicians and pathologists an overview of primary gastrointestinal lymphomas.

Microsatellite instability in gastric MALT lymphoma

The role of microsatellite instability and defects in DNA mismatch repair mechanism in the pathogenesis of gastric lymphoma of mucosa-associated lymphoid tissue (MALT) type is still controversial, as both negative and positive findings have been reported. This may be explained mainly by arbitrary selection of the tested loci, the use of various techniques of microsatellite instability analysis and by different definitions of replication error positive phenotype. The aim of our study was to evaluate the instability at selected microsatellite markers using the GeneScan Analysis Software. DNA from paraffin-embedded tissue blocks of 13 previously untreated patients with localized gastric MALT lymphoma was extracted. Five microsatellite markers, which are located in hMSH2, hMLH1, P16, APC and MLL loci, were selected from the genetic database. We found genetic instability in tumors of 9/13 patients with gastric MALT lymphoma (69%). Seven of them had replication-error-positive phenotype (54%). Microsatellite instability was found in 39% of the samples in the MLL locus, 39% in the APC, 46% in the P16, 23% in the hMLH1 and none in the hMSH2. This study demonstrates that microsatellite instability has more prominent role in pathogenesis of gastric MALT lymphoma than reported to date. We suggest that microsatellite instability should be analyzed with markers adjacent to chromosomal loci that are involved in lymphomas. Our findings support the 'Real Common Target genes' theory of high rate of microsatellite instability in specific genes, which are associated with related tumors.