Immunohistochemical analysis of cell kinetic parameters in colonic adenocarcinomas, adenomas, and normal mucosa

The monoclonal antibody Ki-67 identifies a nuclear antigen that is expressed in proliferating cells in G1, G2, S, and M phases of the cell cycle. An immunoperoxidase method and this antibody were used to identify proliferating cells in sections of colorectal tissues—normal colon (n = 10), colorectal polyps (n = 20), and adenocarcinoma (n = 28). Colorectal adenomas showed a uniform distribution of positive nuclear staining throughout the sections, including the cells of the adenoma surface, while staining in the normal mucosa was confined to the middle third and lower third of the crypts. Areas of polyps with numerous Ki-67-positive epithelial cells invariably showed immature or dysplastic histology and, conversely, glands that lacked such histologic features had low Ki-67 staining frequency or were negative. In adenomas, nuclei located toward the luminal surface of glands were more likely to be Ki-67-positive than those located basally in the cells. The mean Ki-67 score (a measure of positive staining nuclei) for adenomas was 45.5 compared to a mean score of 66.3 for adenocarcinomas in the carcinomas studied ( P < .001). Ki-67 score did not correlate with histologic grade or Duke's stage. Ki-67 staining can be used to characterize the proliferative characteristics of normal colonic mucosa, adenomas, and carcinomas.