[en] Cancers which are unlikely to appear among atomic bomb survirors in excess of natural incidence include skin cancer and bone cancer, as these appear to require for their initiation doses that are incompatible with life if administered on a whole body basis. Although chronic lymphocytic leukemia continues to provide an important exception, and for many sites of cancer there is not yet evidence that radiation has increased incidence above normal levels, the data on A-bomb survivors are otherwise consistent with the hypothesis that the carcinogenic effect of ionizing radiation is general, involving all tissues. Studies of cancer among A-bomb survivors are notably limited with respect to the influence of variables other than dose, age, sex, and time. It seems highly desirable that other risk factors be studied in conjunction with radiation dose and demographic variables in an effort to detect interactions that might provide clues as to the etiology of cancer and as to the mechanisms by which ionizing radiation produces cancer. Provisional estimates suggest that the absolute risk of cancer, in terms of excess cases per 10⁶ person-year rads (T65 dose) are about 1.6 for leukemia, 1.2 for thyroid, 2.1 for breast and 2.0 for lung, when estimation is based on age-ATB groups that have demonstrated these effects. (JPN)