MIB1‐determined Proliferative Activity in Intraductal Components and Prognosis of Invasive Ductal Breast Carcinoma

Intraductal components of breast carcinoma may have prognostic significance. In this study, we divided 181 invasive ductal breast carcinomas into comedo and non‐comedo groups based on intraductal component morphology, and differences between the two groups in clinicopathological variables, including proliferative activity and survival, were assessed. Proliferative activity was evaluated by using MIB1 antibody, which reacts with the cell‐proliferation‐associated Ki‐67 antigen, and was expressed as the number of MIBl‐positive nuclei per 1000 cancer cells in intraductal components (MIB1 labeling index). We also investigated which variables had an impact on survival. The comedo group showed a significantly higher MIB1 labeling index than the non‐comedo group (P < 0.0001). The differences in disease‐free and overall survival between the two groups were not significant (P=0.2477, P=0.2069). Multivariate analysis of the entire series showed the MIB1 labeling index to be an independent prognostic factor predicting both disease‐free survival and overall survival (P=0.0160, P=0.0035). When multivariate analysis was repeated separately for the non‐comedo and comedo groups, the MIB1 labeling index remained the most important variable predicting disease‐free and overall survival in the non‐comedo group (P=0.0122, P=0.0040). Moreover, non‐comedo patients with a high MIB1 labeling index had significantly shorter disease‐free and overall survival than those with a low MIB1 labeling index (P=0.0040, P=0.0402). These findings imply that MIB1‐determined proliferative activity of intraductal components is an independent predictor of survival, and is the most important predictor in non‐comedo cases.