Determination of estrogen receptors in cytologic imprints of breast cancers using immunocytochemical methods.

Immunostaining of estrogen receptors (ERs) was carried out on imprints of 62 breast carcinomas using monoclonal antibodies and a sensitive immunoperoxidase technique (the Abbott ER-ICA kit). The results were compared to those obtained by the conventional biochemical analysis of cytosol proteins and to the degree of tumor differentiation. The cytologic specimens were insufficient for analysis in 6 cases; of the remaining 56 cases, 37 (66%) showed a positive ER reaction. In 51 cases with both types of ER analysis, the immunocytochemical staining of the imprints correlated strongly with the biochemical analysis in 44 cases and weakly in 3. Four cases were negative immunocytochemically and positive biochemically. Among the ductal carcinomas, well-differentiated tumors had higher percentages of ER-positive cells than did poorly differentiated tumors. These results show that the immunoperoxidase method is a highly specific and sensitive technique for the evaluation of ER content; it may be applicable to small samples of tumor tissue and may provide additional information for identifying hormonally responsive breast tumors.