Cytologic assessment of tumor cell kinetics: Applications of monoclonal antibody Ki‐67 to fine‐needle aspiration smears

Rates of tumor‐cell proliferation often provide prognostic information about a given neoplasm. Previously available methods for accessing cell kinetics are time consuming and expensive, and often require special equipment or radioactive reagents. Monoclonal antibody Ki‐67 binds a nuclear antigen expressed in proliferating but not in resting cells. We studied Ki‐67 immunostaining of fine‐needle aspiration smears from 40 benign and malignant masses. Labeling indices ranged from 0 (thyroid follicular adenoma) to 75 percent (pulmonary oat‐cell carcinoma). Frozen section immunostaining (11 cases) and flow cytometric assessment of cell proliferation (8 cases) were in good agreement with Ki‐67 labeling indices on smear material. We suggest that this method provides a rapid, inexpensive, and dependable means of assessing tumor‐cell kinetics in cytologic preparations.