Immunoperoxidase studies by monoclonal antibody B72.3 applied to breast aspirates: diagnostic considerations.

The purpose of this study was to determine the reactivity of monoclonal antibody (MAb) B72.3 when applied directly to aspiration biopsy cytology (ABC) of the breast in the following conditions: (1) infiltration lobular carcinoma; (2) fibrocystic disease; (3) fibroadenoma; and (4) apocrine cysts. Nine of ten aspirates from infiltrating lobular carcinoma were positive in these assays, while 21 of 22 benign cases reacted negatively. The single false-positive benign aspirate manifested a staining pattern characteristic of apocrine cells. This study demonstrates that the MAb B72.3 can be employed as a potentially valuable diagnostic adjunct. It can be used on stained aspirates to assist in the interpretation of ABC from breast lesions.