MICROSATELLITE INSTABILITY AND LOSS OF HETEROZYGOSITY IN GASTRIC LYMPHOMA

To evaluate the significance of microsatellite instability (MI) and lo ss of heterozygosity (LOH) in the development of gastric lymphoma, we examined 33 tissue-samples of 20 primary gastric B-cell lymphomas (6 l ow-grade lymphomas of mucosa-associated lymphoid tissue [MALT; 10 samp les] and 14 diffuse large B-cell lymphomas [23 samples]). MI and LOH w ere evaluated at 13 microsatellite loci. In MALT lymphoma, four of six cases showed MI at one to two microsatellite loci (average 1.0 per ca se, 0.8 per sample), whereas in diffuse B-cell lymphoma, all samples s howed MI at one to five microsatellite loci (average 2.4 per case, 2.7 per sample) (p < 0.05 and p = 0.0001). MI at the c-myc gene locus was most frequent in both types of gastric lymphomas (3 of 6 and 11 of 14 cases, respectively). Regional heterogeneity of the MI pattern was ob served in two of four cases of MALT lymphoma and in four of five cases of diffuse B-cell lymphoma. On the other hand, LOH was observed only in one MALT lymphoma and in three diffuse B-cell lymphomas. Genetic in stability may be an important mechanism for the development and progre ssion of gastric lymphoma. Frequent MI at the c-myc locus might reflec t an activated state and the importance of this gene in mucosal lympho cytes of chronic gastritis.