Ki-67 expression is a prognostic marker of prostate cancer recurrence after radical prostatectomy

Purpose: We assessed the cellular proliferation of clinically localized prostate cancer by immunohistochemistry using the monoclonal antibody MIB to Ki-67 antigen in an attempt to identify associations between proliferative indexes and disease progression following radical prostatectomy. Materials and Methods: Ki-67 proliferative antigen was evaluated using MIB 1 monoclonal antibody in archival paraffin embedded radical prostatectomy specimens from 180 patients followed for 1 to 9 years (mean 4.4). The percentage of tumor nuclei expressing Ki-67 antigen was measured and assigned an MIB 1 score (none or rare-negative, 1+-low score and 2 to 4+-high score) and analyzed for prostate specific antigen, stage, age, race, grade and serological recurrence postoperatively. Results: There was a significant association between MIB 1 score and nuclear grade (p <0.001), Gleason score (p <0.001) and pathological stage (p = 0.01). Patients with a high MIB 1 score had earlier progression and a lower 5-year recurrence-free survival rate (44%) than those with negative MIB 1 scores (71%, p <0.001). In multivariate Cox regression analysis with backward elimination, pathological stage (p <0.01), pretreatment prostate specific antigen (p = 0.04) and MIB 1 score (p = 0.05) were statistically significant predictors of disease-free survival, and patients with a high MIB 1 score were 3.1 times as likely to have recurrence as those with a negative score. Controlling for stage, patients with organ confined disease and a high MIB 1 score had a lower 5-year disease-free survival rate (68%) than those with a low MIB 1 score (95%, p <0.01). Conclusions: Proliferative activity as measured by the Ki-67 proliferative antigen, MIB 1, appears to be a prognostic marker of recurrent prostate cancer after radical prostatectomy.