788P - Efficacy of Enzalutamide (Enza) Following Abiraterone Acetate (Abi) in Chemotherapy-Naïve Metastatic Castration-Resistant Prostate Cancer (Mcrpc) Patients (Pts)

Abstract

ABSTRACT Aim: The activity of ENZA after prior treatment with both of ABI and docetaxel (D) has been examined in several retrospective studies. However, there are limited data on the efficacy of ENZA following ABI in chemotherapy-naive mCRPC pts. Methods: The British Columbia Cancer Agency (BCCA) Cancer Registry was searched for mCRPC pts who received ENZA after prior ABI. Outcomes on ENZA were compared between D-naive and D-experienced pts using K2 for confirmed PSA response (decline ≥ 50% from baseline) and log-rank test for time to progression (radiological and/or clinical) and overall survival (OS). Univariate analysis was performed to identify variables associated with confirmed PSA response on ENZA, using either K2 for categorical variables or logistic regression for continuous variables. Results: 115 pts received ENZA after ABI: 68 had received prior D and 47 were D-naive. The confirmed PSA response rate was 23%, median time to progression was 5.3 months and median OS was 10.58 months. Notably, no significant differences were seen between D-experienced and D-naive pts for PSA response (22% vs. 26%, P = 0.78), median time to progression (4.63 months vs. 6.64 months, P = 0.62) and median OS (10.58 months vs. 8.64 months, P = 0.17) (Table). No clinical variables (including prior response to ABI) were found to significantly associate with PSA decline ≥ 50% on ENZA. Outcomes with ENZA treatment following ABI in mCRPC pts Characteristic (95% CI) Docetaxel-experienced (n = 68) Docetaxel-naive (n = 47) P PSA decline ≥ 50%, n (%) None 15 (22, 14-33) 29 (43, 32-54) 24 (35, 25-47) 12 (26, 15-40) 17 (36, 24-51) 18 (38, 26-53) 0.78 Median time on treatment (months) 4.11 (2.99-5.23) 4.63 (2.58-6.68) 0.71 Median time to progression (months) 4.63 (3.11-6.15) 6.64 (2.82-10.46) 0.62 Median overall survival (months) 10.58 (7.16-14.00) 8.64 (6.57-11.71) 0.17 Conclusions: Anti-tumour activity of ENZA following ABI was comparable in D-experienced and D-naive pts, suggesting that D is not linked to cross-resistance between ENZA and ABI. Identifying clinical and/or molecular factors predictive of response to ENZA after ABI remains a high priority for future research. Disclosure: A.A. Azad: has received research funding (AUS$10000) from Astellas Australia; B.J. Eigl: has received an educational grant from Janssen; K.N. Chi: has received research funding from Astellas and Janssen and acted as a consultant to Astellas and Janssen. All other authors have declared no conflicts of interest.