Immunohistochemical staining with monoclonal Ab B72.3 in benign and malignant breast disease

A variety of benign and malignant breast lesions were evaluated for their reactivity with the monoclonal antibody B72.3. The lesions included invasive duct carcinoma (15 cases), apocrine carcinoma (18 cases, nine invasive and nine in situ lesions), well-differentiated (tubular) carcinoma (15 cases), invasive lobular carcinoma (10 cases) and lobular neoplasia (10 cases), intraductal hyperplasia (nine cases), atypical intraductal hyperplasia (eight cases), intraductal carcinoma (15 cases), sclerosing adenosis (15 cases), and apocrine metaplasia (24 cases). Only 20% of the invasive ductal carcinomas and 27% of the intraductal carcinomas showed a positive reaction for B72.3. Ten percent of the lobular neoplasias and 25% of the invasive lobular carcinoma reacted with B72.3. None of the 15 tubular carcinomas or the 15 cases of sclerosing adenosis reacted. One of eight examples of atypical intraductal hyperplasia (12.5%) showed a positive reaction, but none of the nine intraductal hyperplasias reacted with B72.3. The most consistently positive results were observed in cases displaying apocrine metaplasia. A positive reaction was observed in 23 of the 24 cases of apocrine metaplasia (96%) and 17 of 18 cases of apocrine carcinoma (94%). Thus we conclude that B72.3 is neither specific nor sensitive for the detection of malignant breast lesions. However, it does appear to be a valuable marker for the presence of apocrine differentiation, which is not a known precursor of carcinoma.