Background: During a population-based local cancer registry, a peculiar type of T-cell lymphoma restricted to the gastrointestinal tract was found in patients living in southwestern Japan.

Methods: Five cases of gastrointestinal (GI) tract T-cell lymphoma were analyzed with immunohistologic examination, ultrastructural analysis, in situ hybridization (ISH), and polymerase chain reaction (PCR).

Results: All cases satisfied the criteria of primary GI tract lymphoma at presentation or operation. Four showed a close relationship to human T-cell lymphotropic virus type I (HTLV-I). Those four had positive results for anti-HTLV-I antibody and positive surface markers for CD4, positive hybridization signals by ISH, and HTLV-I gene products by PCR, but they had no lymphoma cells in peripheral blood or bone marrow. The fifth case showed negative signals by ISH and PCR.

Conclusions: These findings suggest that some of the putative adult T-cell leukemia/lymphoma (ATLL) types can be further classified as GI-tract-type lymphoma. The prognosis for the GI tract type is as poor as it is for conventional ATLL.