Prognostic impact of proliferation-associated factors MIB1 (Ki-67) and S-phase in node-negative breast cancer.

MIB1 proliferation rate (MIB1-PR) and total S-phase fraction (SPF) were retrospectively determined in formalin-fixed, paraffin-embedded sections of 90 primary node-negative breast carcinomas. None of the patients had received adjuvant systemic therapy. Median follow-up in patients still alive at the time of analysis was 37.5 months (16-72 months). Immunostaining of Ki-67 antigen was performed using the monoclonal antibody MIB1 and the APAAP technique. An adjacent 50-microm paraffin section was used for flow cytometric S-phase determination. Results were compared to established clinicopathological prognostic factors. MIB1-PR was significantly correlated to grading (P = 0.018); SPF was significantly correlated with tumour size (P = 0.041) and inversely with steroid hormone receptor status (P = 0.03). A significant correlation between MIB1-PR and SPF was found in aneuploid (P = 0.025) but not in diploid tumours (P = 0.164). In univariate analysis, both MIB1-PR (optimized cut-off of 25%) and SPF (optimized cut-off of 8%) were significant prognostic factors for disease-free survival (DFS) (MIB1-PR, P = 0.0224; SPF, P = 0.0028). In multivariate analysis, however, only SPF remained significant; it was the strongest prognostic factor for DFS (P = 0.0073), stronger than MIB1-PR or established clinicopathological prognostic factors. We thus conclude that MIB1-PR and SPF provide additional prognostic information in node-negative breast cancer. However, in our study, flow cytometrically determined SPF had the greater prognostic impact.