MIB-1 antibody staining discriminates the cells in phases other than G0 of the cell cycle. The current study examined the proliferative activity assessed by MIB-1 antibody in colorectal adenoma, primary lesions of colorectal carcinoma (CRC) to investigate the relation between the histologic atypia, the proliferative, infiltrative, and metastatic activities. The MIB-1 antibody positive rate was immunohistologically determined in primary lesions in 311 patients, 22 having adenoma or carcinoma in situ, 207 invasive CRC without distant metastasis, and 82 invasive CRC with distant metastasis. The MIB-1 antibody positive rate was significantly higher in cases of adenoma with severe atypia and carcinoma in situ, showing a close relation between histologic atypia and proliferative activity. Among invasive CRC, the positive rate in poorly differentiated adenocarcinoma and mucinous carcinoma is significantly lower than in well differentiated and moderately differentiated adenocarcinomas. The positive rate was significantly lower in carcinomas with subserosa or deeper invasion than in carcinomas with submucosa or muscularis propria invasion, showing no distinct relation between the proliferative activity and the infiltrative activity. The positive rate of primary lesion was significantly lower in cases with metachronous liver or lung metastasis than in synchronous cases, indicating that metachronous hematogenous metastasis occurs even in cancers with low proliferative activity. The MIB-1 antibody positive rate showed a close relation between histologic atypia and proliferative activity in mucosal colorectal tumors although its relation with infiltrative activity was unclear in invasive CRC. It was apparent that metachronous hematogenous cancer metastasis might take place even in cases with low proliferative activity.

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