Immunohistochemical analysis of benign and malignant papillary lesions of the breast.

The histocytological diagnostic criteria and recently developed immunohistochemical procedures selective for either the epithelial or the myoepithelial mammary cells have been tested in a series of 60 cases of papillary lesions of the breast. These included 15 benign solitary intraductal papillomas, 41 papillary carcinomas (29 pure and 12 associated with other types of in situ or invasive ductal carcinoma), and four cases of "suspected" papillary carcinomas. Markers for epithelial cells (EMA) and for apocrine metaplasia (GCDFP-15) did not permit a distinction between benign and malignant papillary lesions; however, immunocytochemical staining for CEA using monoclonal antibodies, and for actin (a marker of the myoepithelial cells) was discriminative in this respect. Benign papillomas have a basal layer of actin-rich myoepithelial cells; the cytoplasm of the epithelial cells is CEA negative. Papillary carcinomas lack the myoepithelial layer, except in areas where multiple papillomas are present, associated with ductal or papillary cancer. CEA was detected in 85% of carcinomas. Two of the cases of "suspected carcinoma" lacked myoepithelial cells and were interpreted as carcinomas. It is concluded that the immunocytochemical methods for cell markers can offer valuable data in the study and diagnosis of papillary lesions of the breast; it is difficult, however, to be categorical in borderline cases since in our experience, the behavior of the malignant papillary lesions of the breast is usually favorable. Residual foci of multiple intraductal papillomas were found in seven cases of papillary carcinoma, supporting the pre-neoplastic potential of this condition.