Incidence and characterization of antiandrogen withdrawal syndrome (AAWS) after enzalutamide (ENZA) in patients (pts) with metastatic castration-refractory prostate cancer (mCRPC).

Abstract

228 Background: AAWS manifested as PSA decline after discontinuation of first generation AAs, like bicalutamide, has been well characterized and reported. Objective of this study was to assess the incidence and characterize AAWS after ENZA in pts with mCRPC. Methods: From a single institution cohort, pts with mCRPC who discontinued ENZA after documented disease progression per PCWG2 criteria were included. AAWS after ENZA was defined as any degree of PSA decline after discontinuation of ENZA. Baseline pts, disease, and treatment characteristics were compared between Òpts with AAWS after ENZAÓ vs. Òpts without AAWS after ENZAÓ treated during the similar time period: median values were compared with the Wilcoxon rank sum test; proportions were compared with FisherÕs Exact test; and the log rank test was used to compare PFS (Table). Results: 5 pts of 72 eligible pts (~7%) experienced AAWS after discontinuation of ENZA. The levels of PSA decline were as follows: 84%, 32%, 17%, 15% and 15%, respectively. Median AAWS response time, until subsequent PSA progression, was 6 weeks. None of the pts, disease or treatment characteristics (such as prior duration of response to ENZA) were different among Òpts with AAWS after ENZAÓ vs. Òpts without AAWS after ENZAÓ. Conclusions: This is the largest study reporting on the incidence and characterization of AAWS after ENZA. AAWS after ENZA is infrequent (~7%), of short duration (6 weeks), and not predicted by pts, disease or treatment related characteristics. Unlike AAWS after first generation AR inhibitors, like bicalutamide, the AAWS after ENZA is not clinically meaningful and should not have any bearing on the eligibility criteria of clinical trials conducted in the post ENZA setting. [Table: see text]