Monoclonal antibody B72.3. An adjunct for evaluation of suspicious aspiration biopsy cytology from the breast.

Monoclonal antibody B72.3 (MoAb B72.3) is a potentially valuable diagnostic adjunct when applied to aspiration biopsy cytology (ABC). In this prospective study, its reactivity was tested on the ABC from 25 breast lesions interpreted as suspicious. The stain was applied directly to the Papanicolaou-stained specimen by the avidin-biotin peroxidase methodology at a concentration of 40 micrograms/ml. In 11 aspirates from invasive carcinomas, the reactivity to MoAb B72.3 was strongly positive in nine cases and weakly positive in two. Ten of these tumors were homogeneous or heterogeneous infiltrating lobular neoplasms, tumors causing special diagnostic pitfalls by ABC. The cells from seven of the nine benign lesions were nonreactive, and in two cases from fibrocystic change, weakly reactive. The ABC from five patients with noninvasive carcinomas or atypical lobular hyperplasia showed a variety of responses. The findings indicate that in select circumstances, MoAb B72.3 used in conjunction with clinical and cytologic findings may be a useful diagnostic adjunct.