The Clinical Outcome of Second Generation Anti-Hormonal Therapy in Patients with Metastatic Castrate-Resistant Prostate Cancer Following CHAARTED Regimen.

e17044 Background: Prostate cancer (PC) is the most common malignancy in men. Treatment for metastatic PC historically had been androgen-deprivation therapy (ADT) alone. Docetaxel and ADT became standard of care for treating metastatic hormone sensitive prostate cancer (mHSPC) after CHAARTED trial was reported in 2014. Progression-free survival (PFS) and overall survival (OS) were significantly longer with combination of docetaxel and ADT. Treatment for metastatic castrate-resistant prostate cancer (mCRPC) after docetaxel in hormone sensitive setting is not established. Second generation antihormonal drugs, enzalutamide and abiraterone, were established in treatment of mCRPC before CHAARTED, but the clinical outcome of mCRPC patients after chemo-hormonal therapy has yet to be reported. Methods: We are conducting a single institution, retrospective study of patients who developed mCRPC after docetaxel-ADT and then treated with abiraterone or enzalutamide, based on clinician’s choice, from 2016 to 2018. Primary endpoint is OS. Secondary endpoints are radiographic PFS, time to prostate-specific antigen (PSA) progression, and PSA response rate. Results: Of the 17 patients identified, 13 got abiraterone and 4 got enzalutamide. Four of thirteen patients progressed on abiraterone with median PFS of 8.5 months (mos). Median time to PSA progression was 7 mos. The longest PFS was 16 mos on abiraterone. No patient on enzalutamide progressed to date. PSA response rate was 69% for abiraterone and 75% for enzalutamide. OS has not been reached. Conclusions: Our results show increased radiographic PFS of 3 mos on abiraterone as first line treatment for mCRPC after CHAARTED protocol as compared to results of trial COU-AA-301 in which mCRPC patients received abiraterone second line after docetaxel. Time to PSA progression was 7 mos here and 10 mos in COU-AA-301, however our study has limited patients. Our results indicate the potential benefit of giving abiraterone in mCRPC after docetaxel-ADT. Chemo-hormonal therapy is standardized initial treatment for mHSPC, therefore, the use of second generation antihormonal drugs to treat mCRPC requires further exploration.