Malignant lymphomas in Japan: epidemiological analysis on adult T-cell leukemia/lymphoma.

According to the Vital Statistics Japan Series in 1950-1981, the age-adjusted death rate for malignant lymphomas (ICDs, 200-202) in Japan has increased in recent years. A geographical clustering of malignant lymphomas in the Kyushu districts was observed both in the period 1969-1971 and more recently in 1979-1981. The excessive rate of malignant lymphomas in Kyushu was due to the high incidence of adult T-cell leukemia/lymphoma (ATLL). The distribution of healthy carriers of ATLV, a human retrovirus which is almost identical to HTLV, was closely related to that of patients with ATLL in Japan. Epidemiological features of the infectious mode of ATLV suggested two main routes of natural transmission, one from mother to child and the other from husband to wife. ATLV is considered to be a main causative agent of ATLL from virological and epidemiological evidence, but infection by this virus alone may not result in ATLL because the incidence of ATLL among ATLV carriers was apparently not very high even in endemic areas of ATLL. Thus, some risk factors other than ATLV, such as environmental and genetic factors, may contribute to the development of ATLL.