Ki-67 Staining Is a Strong Predictor of Distant Metastasis and Mortality for Men With Prostate Cancer Treated With Radiotherapy Plus Androgen Deprivation: Radiation Therapy Oncology Group Trial 92–02

Abstract

PurposeThe Ki-67 staining index (Ki67-SI) has been associated with prostate cancer patient outcome; however, few studies have involved radiotherapy (RT) -treated patients. The association of Ki67-SI to local failure (LF), biochemical failure (BF), distant metastasis (DM), cause-specific death (CSD) and overall death (OD) was determined in men randomly assigned to short term androgen deprivation (STAD) + RT or long-term androgen deprivation (LTAD) + RT.Patients and MethodsThere were 537 patients (35.5%) on Radiation Therapy Oncology Group (RTOG) 92-02 who had sufficient tissue for Ki67-SI analysis. Median follow-up was 96.3 months. Ki67-SI cut points of 3.5% and 7.1% were previously found to be related to patient outcome and were examined here in a Cox proportional hazards multivariate analysis (MVA). Ki67-SI was also tested as a continuous variable. Covariates were dichotomized in accordance with stratification and randomization criteria.ResultsMedian Ki67-SI was 6.5% (range, 0% to 58.2%). There was no difference in the distribution of patients in the Ki-67 analysis cohort (n = 537) and the other patients in RTOG 92-02 (n = 977) by any of the covariates or end points tested. In MVAs, Ki67-SI (continuous) was associated with LF (P = .08), BF (P = .0445), DM (P < .0001), CSD (P < .0001), and OD (P = .0094). When categoric variables were used in MVAs, the 3.5% Ki67-SI cut point was not significant. The 7.1% cut point was related to BF (P = .09), DM (P = .0008), and CSD (P = .017). Ki67-SI was the most significant correlate of DM and CSD. A detailed analysis of the hazard rates for DM in all possible covariate combinations revealed subgroups of patients treated with STAD + RT that did not require LTAD.ConclusionKi67-SI was the most significant determinant of DM and CSD and was also associated with OD. The Ki67-SI should be considered for the stratification of patients in future trials.