Assessment of tumor cell kinetics by immunohistochemistry in carcinoma of breast

Cell proliferation was assessed in 33 invasive breast carcinomas by an immunoperoxidase procedure using the monoclonal antibody, Ki‐67, which reacts with a nuclear antigen in proliferating cells. The antibody labeled a variable proportion of tumor cells ranging from 3% to 60%. High numbers of Ki‐67‐positive cells were found in tumors with high mitotic rates, high nuclear grade, high histologic grade, and in premenopausal women. Tumors with low and intermediate Ki‐67 labeling rates often had high estrogen receptor content, whereas tumors with high Ki‐67 labeling rates were usually estrogen receptor negative. These correlations are similar to those previously reported for other measurements of cell cycle kinetics such as thymidine labeling index and suggest that immunohistochemical staining of invasive breast carcinoma for the Ki‐67 epitope may provide cell cycle information not otherwise readily available to the clinician and may be useful in assessing prognosis in carcinoma of the breast.