Immunocytochemistry with monoclonal antibody B72.3 applied to a spectrum of benign and malignant breast aspirates--strengths and pitfalls.

Fine needle aspiration cytology (FNA) was performed on 168 breast masses. In all cases aspirates were reacted with monoclonal antibody (MAb) B72.3 using the ABC immunoperoxidase technique. MAb B72.3 demonstrated reactivity in nine of 90 malignant cases in which the cytologic diagnosis was not positive. In eight benign cases in which the cytopathologist made a suspicious diagnosis, MAb B72.3 demonstrated cytoplasmic reactivity in only one case. In three cytologically benign cases MAb B72.3 reacted strongly positive. The overall diagnostic accuracy of this immunoperoxidase technique was approximately 95 percent. In about five to 10 percent of cases, monoclonal antibody B72.3 can be a valuable diagnostic adjunct to routine cytopathologic diagnosis. False positives present pitfalls that must be considered.