Utility of the percentage of positive prostate biopsies in predicting PSA outcome after radiotherapy for patients with clinically localized prostate cancer.

Abstract

To determine the utility of the percentage of positive prostate biopsies (PPPB) in predicting prostate-specific antigen (PSA) outcome after external beam radiotherapy alone. The records of 750 clinical Stage T1 and T2 patients treated by external beam radiotherapy alone with a median follow-up of 80 months were reviewed. Of the 750 patients, 345 were eligible for analysis; 255 (74%) had undergone sextant biopsies, 28 (8%) <6 biopsies, and 62 (18%) >6 biopsies. The pretreatment PSA level (<10, 10-20, >20 ng/mL), biopsy Gleason score (2-6, 7, 8-10), and clinical stage (T1-T2a, T2b, T2c), uni- or bilateral positive biopsy, radiation dose, and PPPB were analyzed as potential predictors of PSA outcome. The PPPB data were analyzed as a continuous and as a categorical variable. PPPB was a significant predictor of the time to PSA failure on univariate analysis as a continuous (p = 0.0053) and as a categorical (<50% vs. >or=50%, p = 0.0077) variable. In multivariate analysis, a trend was noted for worse 5-year PSA failure-free survival based on PPPB >or=50% vs. <50% (p = 0.082). Sixty-four patients experienced biochemical failure according to the American Society for Therapeutic Radiology Oncology definition. The 5-year PSA failure-free survival rate was 79% vs. 69% (p = 0.02) and the clinical disease-free survival rate was 97% vs. 86% (p = 0.0004) for patients with <50% vs. >or=50% PPPB. PPPB was not a significant predictor for the time to PSA failure within the traditional risk groups (low, intermediate, and high) on multivariate analysis. PPPB was a predictor of post-external beam radiotherapy PSA outcome in clinically localized prostate cancer; but in this cohort it did not provide additional information beyond the traditional risk stratification schema.