Long follow-up quality of life outcomes from an investigator-initiated randomized trial of enzalutamide versus abiraterone plus prednisolone in docetaxel-untreated castration-resistant prostate cancer.

52 Background: Head-to-head comparison between enzalutamide (ENZ) and abiraterone plus prednisolone (ABI) demonstrated similar survival benefit for castration-resistant prostate cancer. We analyzed quality of life (QOL) reported over time in each treatment arm as sub-analysis study. Methods: ENABLE study for PCa, an investigator-initiated, multicenter, phase 3 randomized controlled trial, was conducted. FACT-G QOL questionnaires were reported by patients at timepoints. We analyzed questionnaires up to 48 months, including the detailed assessment of subscales which consist of physical, social, emotional, and functional well-being. Results: In total 92 patients in each arm included, 79 and 77 in the ENZ and ABI arm answered questionnaires up to 24 months. There were no significant differences in overall survival and time to PSA progression between arms (P=0.4365 and P=0.2458). Although ENZ did not change the total score of FACT-G during treatment (P=0.8552), ABI significantly deteriorated it gradually (P=0.0002). In ABI arm, the standard dose (1000 mg/day) significantly deteriorated the total score of FACT-G chronologically (n=57, P=0.0002), meanwhile the modified dose (750 mg/day or less) did not change it during treatment (n=15, P=0.1816). In the subscale analysis, ENZ did not deteriorate any subscales, whereas ABI deteriorated social and functional well-beings (P=0.0149 and P=0.0005, respectively). Further dissection of subscale analysis revealed that the modified dose of ABI did not deteriorate social and functional well-beings (P=0.277 and P=0.4026, respectively) but the standard dose of ABI significantly deteriorated them (P=0.0010 and P<0.0001, respectively). Conclusions: A head-to-head comparison of QOL between ENZ- and ABI-treated castration-resistant prostate cancer patients was performed for the first time. ABI deteriorated QOL chronologically and the standard dose of ABI was a main cause of the deterioration in QOL. The modified dose of ABI may be a better treatment option. Clinical trial information: UMIN000015529 .