The real-world benefit of novel androgen receptor-targeting agents (ARTA) before and after docetaxel in CRPC with bone metastases in Japan: A subanalysis of the PROSTAT-BSI, a prospective observational study before and after approval of novel ARTAs.

Abstract

43 Background: ARTAs (enzalutamide and abiraterone) have been approved for relapse of prostate cancer in Japan since 2014. However, the efficacy of ARTAs for overall survival (OS) has not yet been proven in Japanese real-world clinical practice. Bone Scan Index (BSI), amount of bone metastasis in a unit of %, has become available for bone scintigraphy using software of BONENAVI (EXINIbone) in Japan. To confirm the benefit of BSI, we conducted a prospective observational study from 2012 to 2017 on mHSPC and mCRPC prior to docetaxel (presented at ASCO-GU 2020). Then we conducted this subanalysis to investigate the real-world benefit of ARTAs on OS before and after docetaxel. Methods: Patients enrolled as the mHSPC (N = 148) and mCRPC (N = 99) groups in the PROSTAT-BSI registry over a 3-year observation period were analyzed with or without ARTAs or flutamide. Patients were evaluated for PSA progression, BSI progression, and OS during hormonal therapy or chemotherapy. Results: In the mHSPC group, 123 patients were treated with combined androgen blockade (androgen deprivation + 80 mg bicalutamide) as an initial hormonal therapy. Thirty-seven patients were treated with flutamide after PSA progression. Thirty-seven patients were also treated with ARTAs as 2nd or later. Docetaxel was used in 25 patients. There was no significant difference in PSA (median: 265.5 and 248.0 ng/mL; P = 0.877) and BSI (median: 1.28% and 1.68%; P = 0.131) between the ARTA (-) and ARTA (+) groups at the start of hormonal therapy, respectively. Despite a median PSA-PFS disadvantage of 16 months in the ARTA (+) group compared to the ARTA (-) group (median: 8.9 and 25.2 months), OS of both groups were comparable (3-year survival rate: 84.0% and 75.7%; HR [95% CI]:0.556 [0.238-1.299], P = 0.232), respectively, indicating favorable effect of ARTA on OS. Furthermore, OS tended to be more extended in patients who received flutamide prior to ARTAs (N = 21) (HR [95% CI]:0.3175 [0.050-2.026], P = 0.225). In the mCRPC group, 8 patients who used ARTA prior to docetaxel were excluded from this analysis. ARTAs were used to treat relapse after docetaxel in 44 patients. Cabazitaxel was used in 14 patients. There was no significant difference in PSA (median: 16.8 and 26.8 ng/mL; P = 0.240) and BSI (median: 2.43% and 1.48%; P = 0.105) between the ARTA (-) and ARTA (+) groups at the start of docetaxel, respectively. There was no significant difference in PSA-PFS between the ARTA (-) and ARTA (+) groups (median PSA-PFS: 4.3 months and 7.0 months; P = 0.999), but OS was significantly better in the ARTA (+) group in the ARTA (-) group (median OS: 28.9 months vs 21.1 months; HR [95% CI]: 0.484 [0.264-0.888]; P = 0.019). Conclusions: This subanalysis demonstrates the benefit of ARTAs for OS before and after docetaxel in clinical practice.