Phase II safety and tolerability study of Radium-223 (R223) in combination with enzalutamide (ENZA) in patients (pts) with metastatic castration-resistant prostate cancer (mCRPC): CTRIAL-IE (ICORG) 13-21.

5050Background: R223 and ENZA are standard of care agents in the treatment of patients (pts) with mCRPC. The combination of R223 and ENZA is of interest due to differing modes of action and non-overlapping toxicity profiles, leading to the potential for synergy. Methods: This phase II, open-label, multicentre single arm study (NCT02225704) enrolled pts with mCRPC to bone with or without visceral/lymph node involvement who had progressed on androgen deprivation therapy. Prior docetaxel chemotherapy for hormone sensitive prostate cancer was allowed. Pts received 6 cycles of R223 (55 kBq/kg IV Q4W) in combination with ENZA (160mg/day), followed by ENZA alone until disease progression (PD), unacceptable toxicity or consent withdrawal. The primary endpoint was safety for the 6 months of combination therapy which is reported here. Results: From July 2015 to July 2017, 45 pts were enrolled in Ireland. 42 pts (93.3%) received all 6 cycles of combination therapy. A total of 13 pts (28.9 %) had grade (gr) 3/4 adver...