Peripheral T-cell lymphoma in Japan: recent progress.

T-lymphoma, including adult T-cell leukemia-lymphoma (ATL) accounted for 75% of non-Hodgkin's lymphoma in the Kyushu district of Japan and for 43% in the nation as a whole. Human T-cell leukemia/lymphoma virus type I (HTLV-I) is closely associated with ATL; however, 11 (7.5%) of 147 patients with ATL were HTLV-I negative. The cumulative percentage incidence of anti-HTLV-I seropositive ATL patients can be simply described by a Weibull model of the typical tear-off type, suggesting that ATL leukemogenesis may be the result of accumulation of approximately five critical events, most likely somatic mutations within HTLV-I-infected T-cells. ATL is still a difficult disease to treat successfully, while peripheral non-ATL T-lymphoma responded to standard chemotherapy in the same way as B-lymphoma. The disease entity of immunoblastic lymphadenopathy (IBL)-like T-lymphoma was also described. Morphological recognition of focal or sheetlike proliferation of atypical neoplastic pale cells and immunoblasts of T-cell nature were important findings for the diagnosis. Major prognostic factors differed greatly among ATL, peripheral non-ATL T-lymphoma and B-lymphoma. Pathology was not associated with treatment outcome and survival in T-cell diseases. These results indicate that the terms ATL, peripheral non-ATL T-lymphoma, and B-lymphoma should be used instead of the all-inclusive term non-Hodgkin's lymphoma, because of differences in cellular origin, clinical features, treatment outcome, prognosis, prognostic factors, chromosomal aberrations, and etiology.