Reactivity of a monoclonal antibody with tissues and tumors from the human breast. Immunohistochemical localization of a new antigen and clinicopathologic correlations.

The reactions of a monoclonal antibody to the MCF7 breast cancer cell line were immunohistochemically studied on a variety of breast tumors, primary and metastatic, on mammary epithelium and on nonneoplastic breast lesions. A high proportion of positive reactions was observed in ductal, lobular, and tubular carcinomas as well as in mammary Paget's disease. Mucinous, medullary, and papillary carcinomas showed a low incidence of reactivity. Carcinomas with metaplasia, carcinoids, and nonepithelial breast tumors were unreactive with the antibody. Positive immunostaining was documented also in nodal and extranodal metastatic lesions. The staining of nodal metastases was correlated with the positive reaction of the primary tumor. Reactivity was widely distributed in normal breast epithelial cells and in benign breast lesions. Staining of nonneoplastic mammary epithelial was associated with reactivity of adjacent neoplastic tissues. Staining differences between nonneoplastic and neoplastic mammary tissues were related to the intensity and cytologic distribution of the labeling. Heterogeneous reactivity of morphologically similar cells was documented in nonneoplastic and neoplastic breast epithelial cells as well as in nodal and extranodal breast carcinoma metastases. Immunohistologically detectable antigen was not correlated with prognostic factors such as histologic grade or nodal status. A retrospective study of T1NO cases failed to substantiate any prognostic value for the reactivity of primary breast tumors with this monoclonal antibody.