Human T-cell leukemia virus type I Tax genotype analysis in Okinawa, the southernmost and remotest islands of Japan: Different distributions compared with mainland Japan and the potential value for the prognosis of aggressive adult T-cell leukemia/lymphoma

Abstract Okinawa, comprising remote islands off the mainland of Japan, is an endemic area of human T-cell leukemia virus type I (HTLV-1), the causative virus of adult T-cell leukemia-lymphoma (ATL) and HTLV-1-associated myelopathy (HAM). We investigated the tax genotype of HTLV-1 among 29 HTLV-1 carriers, 74 ATL patients, and 33 HAM patients in Okinawa. The genotype distribution—60 (44%) tax A cases and 76 (56%) tax B cases—differed from that of a previous report from Kagoshima Prefecture in mainland Japan ( tax A, 10%; tax B, 90%). A comparison of the clinical outcomes of 45 patients ( tax A, 14; tax B, 31) with aggressive ATL revealed that the overall response and 1-year overall survival rates for tax A (50% and 35%, respectively) were lower than those for tax B (71% and 49%, respectively). In a multivariate analysis of two prognostic indices for aggressive ATL, Japan Clinical Oncology Group-Prognostic Index and Prognostic Index for acute and lymphoma ATL, with respect to age, performance status, corrected calcium, soluble interleukin-2 receptor, and tax genotype, the estimated hazard ratio of tax A compared with tax B was 2.68 (95% confidence interval, 0.87–8.25; P  = 0.086). Our results suggest that the tax genotype has clinical value as a prognostic factor for aggressive ATL.