Background: Gastric T-cell lymphomas are rare, and their incidence and viral status have not yet been fully clarified.

Methods: Sixty-seven cases of surgically resected gastric lymphomas from city hospitals in Tokyo were evaluated. The surface phenotype was determined by immunohistochemistry, gene rearrangement by Southern blot hybridization, association with Epstein-Barr virus (EBV) by EBV-encoded small RNAs in situ hybridization, and the presence of human T-cell lymphotropic virus type 1 (HTLV-1) by serology, Southern blot hybridization, and polymerase chain reaction analysis.

Results: Five of the 67 cases were T-cell lymphoma (7%): 3 cases were HTLV-1 negative (-) and 2 were HTLV-1 positive (+). Systemic eosinophilia was observed in the three HTLV-1(-) gastric lymphomas. Neoplastic cells were morphologically similar in both groups, but a granulomatous reaction with marked eosinophilia was observed only in the two cases of HTLV-1(-) lymphoma. They also had characteristics of natural killer (NK) cell-like T-cell lymphoma, expressing NK markers and TCRgamma gene rearrangement. Positivity with HML-1 (specific for intestinal epithelial T-cells lymphoma was observed in one HTLV-1(+) lymphoma. The EBV gene was detected in only one case of B-cell lymphoma but not in any case of T-cell lymphoma.

Conclusions: Gastric T-cell lymphoma occurs in 7% of gastric lymphomas in Japan and is comprised of HTLV-1-related lymphomas and lymphomas unrelated to HTLV-1, including NK cell-like lymphomas with eosinophilia.