Mammary Paget's disease and associated carcinoma. An immunohistochemical study.

Mammary Paget's disease has been said to result from epidermal spread by contiguity of primary intraductal carcinoma. To assess similar identity, we immunostained Paget's cells and underlying intraductal and/or invasive mammary carcinoma in 20 cases for cytokeratins, epithelial membrane antigen, gross cystic disease fluid protein-15, lysozyme, carcinoembryonic antigen, S100 protein, kappa-casein, and alpha-lactalbumin. Steroid receptor immunostain was positive in only one (5%) of the cases of Paget's disease and in two and four (approximately 15%) (for estrogen and progesterone receptor, respectively) of the cases of ductal carcinoma. In 18 patients (90%), the immunohistochemical profile was identical in Paget's cells and associated carcinoma for seven or more antigens. In one patient, there was a definite disparity in the antigenic profile; in another patient, this was dissimilar because of very focal staining in one site. The antigenic similarity between Paget's cells and underlying carcinoma in 18 (90%) of the cases of mammary Paget's disease suggested in favor of their common origin, ie, probably intraepidermal spread of ductal carcinoma. Origin from apocrine/eccrine structures, or multipotent cells in the epidermis, was suggested in a minority.