Does salvage radiation therapy (SRT) change the biology of recurrent prostate cancer (PCa) based on PSA doubling times (PSADT)? Results from the SEARCH database.

Abstract

203 Background: SRT offers a second opportunity for PCa control after biochemical recurrence in men treated with radical prostatectomy. Although some retrospective data suggest an overall survival benefit, we hypothesized that in men with radio-resistant tumors, SRT may indeed promote transformation to a more aggressive cancer due to radiation-induced mutations. To test this, we used PSADT as a surrogate for cancer aggressiveness and compared PSADT before and after SRT in men who failed SRT. Methods: Of 288 men who underwent SRT in the Shared Equal Access Regional Cancer Hospital (SEARCH) database since 1988, we detected 78 with SRT failure defined as PSA ≥ 0.2 ng/mL above the post-SRT nadir. Of these, 44 had PSADT available before and after SRT, which was compared using Wilcoxon’s paired test with men serving as their own controls. We also tested predictors of PSADT change using multivariable logistic regression. Results: There were no differences in PSADT before and after SRT (10.6 vs. 12.2 months; P=0.85). However, in some individual cases large changes were observed. Only seminal vesicle invasion showed a trend towards an association with a shorter post-SRT PSADT relative to the pre-SRT PSADT (P=0.067). Conclusions: Overall, the PSADT after and before SRT were statistically similar suggesting that after SRT failure, PCa does not emerge with more aggressive biologic features. Further studies are needed to identify predictors and the clinical relevance of individual PSADT changes noted in our study. (Note: Authors R. L. Muller and S. J. Freedland received support from DoD Award Number W81XWH-10-1-0155).