[en] Three hundred and sixty cases of breast cancer were collected from among the 63,000 female members of the RERF extended Life Span Study sample which includes atomic bomb exposed women and controls of Hiroshima and Nagasaki. The relationship of these breast cancer cases to A-bomb radiation was sought, and in studying 5-year survival, the following conclusions were obtained concerning its relationship to histopathological findings: 1) The prognosis of the 50⁺ rad high dose group is the best, followed by the nonexposed group and the low dose group; 2) The apparently better survival may be due, at least in part, to the fact that this group is heavily weighted in favor of those who were younger at the time of the bomb; 3) There is no specificity of the histologic type of breast cancer in the survivors by dose; 4) Nor, is any significant difference observed in the distribution of tumor size and histological grade; 5) Cellular reaction is significantly marked at the stroma of carcinoma tissue in the high dose group; 6) Immune reaction is considered to be strong at the affected site of breast cancer in the high dose group and this can be regarded as a finding suggestive of good prognosis; 7) Further extended studies are therefore warranted. (author)