Utility of prostate specific antigen doubling time (PSA-DT) at the start of androgen independent prostate cancer (AIPC) and immediately before chemotherapy in predicting efficacy of taxane chemotherapy

Abstract

4640 Background: PSA-DT has been used to predict efficacy of various treatments for prostate cancer. No study has evaluated the ability of PSA-DT to predict efficacy of taxane chemotherapy, the standard of care for patients with metastatic AIPC. Methods: PSA-DT was retrospectively calculated in 148 AIPC patients treated with taxane chemotherapy. PSA-DT at the start of AIPC (PSA-DT “at AIPC”) was calculated as log 2 divided by the slope of the linear regression of log PSA vs. time, from the first rise above the PSA nadir on androgen deprivation therapy (ADT) until the start of the next treatment. PSA-DT immediately prior to chemotherapy (“pre-chemotherapy” PSA-DT) was calculated similarly, using the three PSA values closest to and no longer than three months before the start of taxane chemotherapy. PSA-DT was divided into tertiles for analysis. Primary outcome was response to chemotherapy, defined as >50% maximum percent reduction in PSA from the start of chemotherapy and was analyzed using logistic regression. Results: PSA-DT at AIPC and pre-chemotherapy PSA-DT could be calculated for 91 and 109 patients, respectively. Rapid pre-chemotherapy PSA-DT (<5 wks) showed a trend towards higher >50% PSA response rates, when compared with intermediate (5–10 wks) and slow PSA-DT (≥10 wks) (74%, 62%, 54%, respectively, P = 0.08 for trend). At androgen independence, rapid PSA-DT (≤ 6 wks) also showed higher >50% PSA response rates than intermediate (6–12 wks) or slow PSA-DT (>12 wks) (81%, 61%, and 62%, respectively) but were not significantly different (P = 0.07, ≤6 vs. >6 wks). Conclusions: Short PSA-DT directly before taxane chemotherapy and also at androgen independence shows a trend towards higher > 50% PSA response rates. PSA-DT at these timepoints will be important to analyze in larger prospective studies. No significant financial relationships to disclose.