Growth fractions in human prostatic carcinoma determined by Ki‐67 immunostaining

Until recently, [³H]‐thymidine incorporation, DNA analysis by flow cytometry, and cell doubling times have been the main methods of studying tumour cell kinetics. All these techniques are laborious, expensive, and difficult to perform in a routine diagnostic laboratory. This study examined fresh frozen sections from 31 prostatic biopsy specimens with the hybridoma antibody Ki‐67, a marker of proliferating cells, using a modified avidin—biotin—peroxidase complex technique. The percentage of glandular cells decorated by this antibody, representing the growth fraction, was determined for both benign and malignant samples. Benign prostatic glands showed an average Ki‐67 score of 4 per cent, significantly less than the 16·3 per cent mean growth fraction found in prostatic carcinomas. There was a significant correlation between the tumour growth fraction as assessed by Ki‐67 staining, and the histological grade. A positive correlation was also found between the Ki‐67 score and the intensity of staining, and a definite trend was noted between the Ki‐67 score and the tumour clinical stage. Ki‐67 promises to be a useful marker in determining the prognosis of prostatic cancer.