MIB-1 (Ki-67) immunostaining of breast cancer cells in cytologic smears.

Objective: The reliability of immunocytochemical evaluation of proliferation activity was tested using the monoclonal antibody MIB-1 on cytologic specimens.

Study Design: The study comprised 83 frozen tissue smears (FTSs) and 51 fine needle aspirates (FNAs) from 119 breast cancer patients. MIB-1 labeling indexes (LIs) were compared with various tumor parameters assessed on histologic material.

Results: MIB-1 LIs established on cytologic smears were significantly different in ductal and lobular carcinomas (P = .024) and correlated significantly with mitotic activity (P < .0001), histologic grade (P < .0001) and S-phase fraction (P < .0001). Essentially the same results were obtained on FTSs and FNAs.

Conclusion: Proliferative activity can reliably be evaluated by FNA cytology, and the evaluation of MIB-1 LIs may complement cytologic grading of breast cancer. The evaluation of proliferation activity may, therefore, contribute to the selection of candidates for adjuvant chemotherapy.