Abiraterone acetate in patients with metastatic castration-resistant prostate cancer, chemo-naive, who received a prior diethylstilbestrol therapy.

Abstract

130 Background: The use of diethylstilbestrol (DES) for the treatment of metastatic castration resistant prostate cancer (mCRPC) is very common in developing countries. Retrospective data suggests that abiraterone acetate (AA) is active in patients that progressed to DES. This phase II study evaluated the efficacy and safety of abiraterone acetate in chemotherapy-naïve patients with metastatic CRPC who have progressed to DES. Methods: Patients with DES−refractory metastatic CRPC with ongoing ADT, serum testosterone level < 50 ng/dL and ECOG of 0-2 were included. All patients received AA 1,000 mg with prednisone 5 mg once daily in a 28 days cycles. The primary endpoint was the time to PSA progression (PSAP) by PCWG2 and was previously reported. We present here secondary endpoints: overall survival, PSA response, maximum PSA change from baseline and safety. Results: A total of 46 patients were enrolled, median age was 69.8 years, 76% had gleason > = 7 at diagnosis, median time from metastatic disease to DES discontinuation was 25.9 months, and a median duration of prior DES of 7.2 months. AA treatment resulted in median time to PSA progression of 7.3 months. PSA response rate (³ 50%) was 47.5% (95% CI: 36,1% to 68,5%) at 12 weeks and 57.5% (95% CI: 27.0% to 59.1%) at any time. 93.4% received chemotherapy after progression to AA. The median overall survival was 29.6 months. Substantial declines in serum androgens from baseline to week 12 occurred and in this group a higher proportion of PSA responses occurred. The incidence of adverse events (AEs) related to AA was 74% and prednisone 59%. Hypertension (21.7%), fatigue (19.6%) and oedema peripheral (13.0%) were the most frequent AA related AEs. The most frequent prednisone related AEs were hyperglycaemia (15.2%) hypertension (10.9%). Serious AEs occurred in 23.9% of subjects and 3 subjects (6.5%) died of AEs not related to study drugs. Conclusions: AA is well tolerated and demonstrated activity in mCRPC patients previously treated with DES, therefore it should be considered an option in chemo-naïve patients. Serum androgens levels tend to decrease with AA treatment and are associated with PSA responses. Clinical trial information: NCT02217566.