Incidence of adult T-cell leukemia/lymphoma among human T-lymphotropic virus type I carriers in Saga, Japan

Using a population-based cancer registry, we tabulated 69 definite adult T-cell leukemia/lymphoma cases (36 males and 33 females) and 2.20 expected cases (0.95 for males and 1.25 for females) diagnosed from 1981 to 1983 in Saga, Japan. The number of human T-lymphotropic virus type I carriers was computed by applying sex- and age-specific anti-human T-lymphotropic virus type I antibody positive rates among blood donors at the blood center in 1986 to the whole population of Saga Prefecture in 1982. The age-specific incidence rates among male human T-lymphotropic virus type I carriers from 40 to 79 yr of age per 100,000 were significantly higher than those of female carriers (P less than 0.05), and the rates from 60 to 69 yr of age were the highest in both sexes. The annual crude incidence rates among carriers were 115.9 for males and 66.4 for females. The summary incidence rates with 95% confidence intervals were 115.9 (58.4 to 193.0) for males and 65.9 (30.0 to 115.9) for females. The cumulative risks were 4.5% (0.8 to 11.0) for males and 2.6% (0.3 to 7.0) for females. These morbidity figures were assumed to be underestimated partly due to the newly proposed clinical entity of adult T-cell leukemia/lymphoma.