Growth fractions in breast cancers determined in situ with monoclonal antibody Ki-67.

The growth fractions of 160 mammary carcinomas and 30 benign mammary lesions were determined in situ by immunostaining with the monoclonal antibody Ki-67. Benign lesions had a mean value of 3% Ki-67 positive cells, whereas the mean value of mammary carcinomas was 16.6%. A comparison of the mean values of Ki-67 positive cells with the histological grade of the tumours showed a correlation between these two variables--that is, histological grade 1 showed 9%, grade 2 16%, and grade 3 26% proliferating cells. Considering the individual Ki-67 values in the different histological grades, it was evident that there was considerable scatter in the number of proliferating cells, so that the proliferation rates of grades 1, 2, and 3 overlapped each other. This indicates a dissociation between histological grade of malignancy and size of the growth fraction in most breast cancers. Follow up studies are needed to establish which of the two variables--that is, morphological degree of malignancy, or the proportion of Ki-67 positive cells--correlates better with response to treatment and survival in individual cases.