Immunocytochemical evaluation of neoplastic and non-neoplastic breast diseases with Mab A-80

Five hundred breast tissue samples from 404 cases were immunostained with A-80, a murine IgM Mab that recognizes a mucinous glycoprotein associated with exocrine differentiation. Samples included 196 primary breast carcinomas, 30 breast carcinoma metastases, 118 fibrocystic disease (FCD), and a further group of 84 samples of FCD from cases known to have breast carcinoma. These samples represented a broad spectrum of common and rare variants of carcinoma and FCD. Samples of fibroadenomas, lactating adenomas, cystosarcoma phylloides, gynecomastia, and normal breasts were similarly studied. The vast majority of carcinomas, 203/212 (95.7%) were immunoreactive; staining varied in extent and intensity, and was virtually unrelated to histologic type and to the presence or absence of recognizable glands. In samples including in-situ and infiltrating ductal or lobular carcinoma, reactivity was frequently stronger in the infiltrating components. No significant difference in reactivity between primary and metastatic carcinomas was noted. Of the group of 118 FCD, 27 were negative whereas 91 showed focal and weak staining. Seventy-two/84 FCD with associated carcinoma were immunostained; in 13 of those 72, staining was strong and extensive. Fibroadenomas, lactating adenomas, gynecomastia, and normal "resting" and lactating breast samples stained focally or not at all. Our findings indicate that Mab A-80 is an excellent immunohistochemical marker for the overwhelming majority of breast carcinomas whereas it marks weakly or not at all the majority of benign neoplasms and normal breast. Moreover, Mab A-80 recognizes a subset of FCD that includes proliferative variants associated with an increased incidence of carcinoma, and FCD in association with carcinoma. Questions regarding rare breast carcinomas that do not react with Mab A-80 remain unclear; yet, we believe that Mab A-80 is a highly promising marker of malignant and dysplastic breast epithelium.