Chronic lymphocytic leukemia in Hiroshima and Nagasaki, Japan.

C HRONIC LYMPHOCYTIC LEUKEMIA is a rare disease in Japan. Since the Atomic Bomb Casualty Commission ( ABCC ) initiated its leukemia case-detection program in 1950 only a few patients with this disorder have been identified in the cities of Hiroshima and Nagasaki. In this report the incidence of chronic lymphocytic leukemia during a 20 year period in both Hiroshima and Nagasaki is compared with the incidence in Japan and the United States. Throughout most of Japan, chronic lymphocytic leukemia constitutes only 2 to 3 per cent of all leukemia’4 A recent review of 3,454 cases of leukemia that occurred between 1956 and 1961 showed that 2.6 per cent were chronic lymphocytic in type.5 The overall incidence of leukemia in Japan is about 30 per million per year.6 On the basis of these figures the chronic lymphocytic leukemia rate in Japan is about 0.8 per million per year. In the United States the leukemia incidence is about 60 per million per year, with chronic lymphocytic leukemia representing from 20 to 30 per cent of the total.79 Thus, the incidence of chronic lymphocytic leukemia in the United States is about 15 per million per year, about 20 times that of Japan. The virtual absence of this type of leukemia in Japan, however, does not entirely account for the great disparity in the leukemia rates of Japan and the United States.