RESUMEN
AB isoantigens are widely distributed in human tissues and loss of AB isoantigen expression has been shown to be an early marker for carcinomatous transformation in some tissues. We therefore applied the Specific Red Cell Adherence Reaction (SRCA) for detection and localization of AB isoantigens in tissue to the study of benign and malignant proliferative lesions of the breast. Twenty-nine lesions in 19 patients were studied. AB isoantigen expression in normal breast tissue was found to be largely confined to the mammary duct system. Loss of AB isoantigen expression was a consistent feature of intraductal carcinoma (3 of 3 cases). Proliferative lesions associated with fibrocystic disease also demonstrated varying degrees of isoantigen loss (simple cystic disease, 3 of 8 cases; intraductal hyperplasia, 6 of 7 cases; sclerosing adenosis, 4 of 4 cases; and intraductal papillomatosis, 7 of 7 cases negative for isoantigen). In contrast to other systems, loss of AB isoantigen expression in the breast appears to be a consistent marker of apparently benign proliferative duct lesions associated with fibrocystic disease, as well as duct carcinoma. The early loss of AB isoantigen expression in these histologically benign lesions supports a possible link between fibrocystic disease and mammary carcinoma. In contrast to other tissues, loss of AB isoantigen expression in proliferative breast lesions is not necessarily evidence of malignancy.