Description:
<jats:title>Abstract</jats:title><jats:p>Histologic slides from representative series of breast cancer patients in Boston, where the incidence rate of breast cancer is high, and in Tokyo, where the incidence rate is low, were reviewed by pathologists who did not know the city of origin of the material. Intraductal, medullary and colloid histologic types were relatively more frequent in Tokyo. Also more frequent in Tokyo were tumors with circumscribed margins and a high degree of cellular reaction. Tumors of small‐cell or invasive ductal histologic type and tumors with a high degree of fibrosis were more frequent in Boston than in Tokyo.</jats:p>