From the ABCC-RERF Life Span Study extended sample, there were 4,499 cases in the Pathology Study sample of atomic bomb survivors who had come to autopsy in the period 1960-83. Among 370 subjects who were heavily exposed with an estimated dose (T65D) of 100 rad or more, 72 (about 20%) of them, whose urinary bladder epithelia had been preserved satisfactorily to suit the purpose of this study, were sampled as the index group. An equal number of control subjects were selected from the unexposed

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... oup individually, matched with the index cases by city, sex, age at death, and year of death. However, cases with marked epithelial autolysis and those pathologically diagnosed as urinary bladder cancer were previously excluded from both the index group and control subjects. These 72 pairs of autopsy cases were pathologically studied for the presence or absence of epithelial lesions of the urinary bladder, namely, hyperplasia, dysplasia and carcinoma-in-situ, and the frequencies of appearance of these lesions were compared statistically by x 2 test based on a case-control study design. Carcinoma-in-situ and severe dysplasia were detected in neither the index cases nor the control cases. The risk was relatively higher in the index group than in the control subjects for both hyperplasia and dysplasia (mild and moderate), in particular the relative risk of papillary hyperplasia being about 4.0, but as the total number of cases were small, this was not statistically significant.