LOBULAR INVOLVEMENT IN HUMAN BREAST-CARCINOMA

One hundred twenty-nine cases of breast carcinoma were examined in order to clarify the occurrence of lobular involvement with regard to stromal invasion. Lobular involvement was clearly recognized in 56 cases (43%) having discernible portions of intraductal carcinoma components. The process of lobular involvement was first recognizable as an extension of a few carcinoma cells from intralobular ducts into the acinar lumina. Progressive accumulation of the carcinoma cells resulted in marked swelling and distortion of the involved lobules. During the process, perilobular myoepithelial cells (actin-positive cells) were stretched and disappeared. Subsequently, breaks in the basement membranes were also observed, resulting in stromal invasion of carcinoma cells. The lobular involvement was classified into common and round varieties, possibly reflecting different growth activities of the carcinoma cells. The stromal invasion was initiated by peripheral budding or focal necrosis of the involved lobules. The latter pattern was often observed in comedo carcinoma. It was thus revealed that in breast carcinomas the terminal ductal-lobular units are quite often involved and can become sites of extraductal invasion.