Very early PSA response to abiraterone in mCRPC patients: A novel prognostic factor to predict overall survival.

Abstract

219 Background: In the last years the therapeutic scenario of mCRPC has undergone a radical change with the approval of new drugs. AA is approved for the treatment of mCRPC after failure of ADT in whom chemotherapy (CT) is not yet clinically indicated and for treatment of mCRPC progressed on or after docetaxel (DTX) based chemotherapy. The aim of this study is to evaluate the role of early PSA decline as a marker of response for an early detection of therapy success in mCRPC patients treated with AA. Methods: We retrospectively evaluated 87 pts with mCRPC treated with AA in compassionate use in Napoli, Trento, and Candiolo, Italy. Serum PSA levels were performed after 15, 90 days and then monthly, a time course of serum PSA was obtained. The PSA flare phenomenon was evaluated, according to a confirmation value at least one week apart. The Cox proportional hazards model was used to test the effect of several variables on survival outcomes in multivariate analyses. Results: We have collected data of 87 patients between Sep 2011 and Sep 2014; 75/87 were eligible for correlation analysis. PSA decline was observed in 78.6 % (59/75) of pts. Early PSA response ( ≥ 50% from baseline at 15 days) was found in 56%(42/75) evaluated patients and confirmed in 29 of them after 90 days. In early responders patients (PSA RR ≥ 50% at 15 days), we found a significant statistical advantage in terms of PFS at 1 year, HR 0.28,95% CI 0.12-0.65, p = 0.003, and OS, HR 0.21 95% CI 0.06-0.72, p = 0.01. The median OS was 17,1 months(8,8-25,2). PFS at 1 year and OS reached statistical significance also in the evaluation at 90 days, HR: 0.23 95% CI 0.07-0.77, p = 0.02 and HR: 0.14 95% CI 0.03-0.70, p = 0.02 respectively. Our analysis showed a positive correlation between OS and duration of AA treatment, previous chemotherapy treatment, cumulative dose of docetaxel ≤ 675 mg/m² and previous hormonal therapy duration ( ≥ 2.5 months) for metastatic setting in early responders group. Conclusions: A significant proportion (78.6%) of patients achieved a rapid response in terms of decline of PSA. Early PSA RR ( ≥ 50% at 15 days after start of AA) can provide clinically meaningful information and could be considered a surrogate of longer PFS and OS.