Safety of continued administration of enzalutamide in patients with prostate cancer who showed benefit from prior exposure: A phase 2 open-label extension study.

303Background: Enzalutamide (ENZA), an androgen receptor (AR) inhibitor that blocks multiple steps in the AR signaling pathway, is approved for patients (pts) with metastatic castration-resistant prostate cancer. This Phase 2, open-label, extension study (NCT01534052) evaluated long-term safety of continued ENZA administration. Methods: Prostate cancer pts previously treated with ENZA in Phase I studies (NCT01902251; NCT01911728; NCT02225093) continued to receive ENZA 160 mg/day until the investigator considered it no longer beneficial or consent was withdrawn. The primary end point was safety. Baseline data from the parent studies were used. Results: 52 pts were enrolled and received ENZA treatment (median age, 67 years [range, 54–88]). Median treatment duration was 443 days (range, 63–2010) since first administration and 392 days (range, 3–1926) in the extension study. In the extension, 43 pts (82.7%) experienced ≥1 any grade treatment-emergent adverse event (TEAE) with the most common (≥10% of pts) bei...