Is ethnicity an independent predictor of prostate cancer recurrence after radical prostatectomy?

PURPOSE: Prostate cancer incidence and mortality are higher in black than in white American men. We determined whether ethnicity is an independent predictor of disease recurrence in men undergoing radical prostatectomy.
MATERIALS AND METHODS: We studied 1,468 patients who underwent radical prostatectomy at the University of California, San Francisco or as part of the Cancer of the Prostate Strategic Urological Research Endeavor database, a longitudinal disease registry of patients with prostate cancer. Preoperative characteristics, including age, race, prostate specific antigen (PSA) at diagnosis, clinical T stage, biopsy Gleason score and percent positive prostate biopsies at diagnosis were determined in each patient. Disease recurrence was defined as PSA 0.2 ng./ml. or greater on 2 consecutive occasions after radical prostatectomy or second cancer treatment at least 6 months after surgery. Cox proportional hazards analysis was performed to determine independent predictors of time to disease recurrence. To control for pretreatment disease characteristics simultaneously patients were assigned to previously described risk groups based on clinical tumor stage, PSA at diagnosis and biopsy Gleason score. The likelihood of disease recurrence per risk group stratified according to ethnicity was determined using the Kaplan-Meier method and compared using the log rank test. Additional multivariate analysis was performed in the subset of patients enrolled in Cancer of the Prostate Strategic Urological Research Endeavor on whom education and income information was available.
RESULTS: Disease recurred in 304 of the 1,468 patients (21%). Black ethnicity, serum PSA at diagnosis, biopsy Gleason score and percent positive prostate biopsies were independent predictors of recurrence on multivariate analysis. Black ethnicity remained an independent predictor of disease recurrence in the multivariate model after stratifying patients into risk groups (p = 0.0007). Ethnicity was most important in patients at high risk, in whom estimated 5-year disease-free survival was 65% and 28% in white and black men, respectively. Education, income and ethnicity correlated highly. When education and income were entered into the multivariate model, ethnicity was no longer an independent predictor of outcome after prostatectomy.
CONCLUSIONS: Ethnicity appears to be an independent predictor of disease recurrence after adjusting for pretreatment measures of disease extent in patients undergoing radical prostatectomy. It appears to be particularly important in those with high risk disease characteristics. However, black ethnicity, education and income are highly correlated variables, suggesting that sociodemographic factors may contribute to the poorer outcomes in black patients even after adjusting for differences in pretreatment disease characteristics.