Castration Resistance Accelerates Prostate Cancer Kinetics

ABSTRACT Background Prostate cancer can be an indolent disease with which patients can live for many years. Thus, an understanding of how therapy and its ensuing resistance affect prostate cancer kinetics may guide efforts to determine optimal timing of therapy initiation. Despite the fact that castration has been used as therapy for prostate cancer for more than 70 years, no prior study has systematically quantified the effect of castration resistance on the rate of progression. The prostate‐specific antigen doubling time (PSADT) estimates prostate cancer kinetics and predicts overall survival, but whether PSADT changes as a result of castration resistance is not known. Methods Here, we studied the longitudinal change in the PSADT before castration and following the development of castration resistance in a cohort of 40 patients with prostate cancer. Results The PSADT of castration‐resistant prostate cancer (CR‐PSADT) was markedly shorter than the matched PSADT of castration‐naïve prostate cancer (CN‐PSADT) (median 2.6 months vs. 5.8 months, p < 0.001). The CR‐PSADT positively correlated with the CN‐PSADT and with overall survival. Sensitivity analysis suggested that the PSADT did not change as a function of time during progression when treatment was unchanged. Using a separate cohort of 36 patients with metastatic CRPC, we confirmed a positive correlation of CR‐PSADT with overall survival and identified a negative correlation with the Ki‐67 proliferation index of metastatic tumor biopsies. Conclusions Castration‐resistant prostate cancer is associated with markedly accelerated disease kinetics compared with castration‐naïve prostate cancer. This acceleration of disease progression has the potential to shorten the survival of some patients with indolent disease who are treated prematurely with ADT.