Background: Older men are at a high risk for adverse events (AEs) from androgen deprivation therapy (ADT). In prior studies, peripheral androgen blockade with bicalutamide and Fin was better tolerated but less efficacious than ADT in HNSPCa. The potential syngerism of Enz (a potent antiandrogen) and Dut/Fin (5-a reductase inhibitors for conversion of testosterone [T] to dihydrotestosterone [DHT]) provided the rationale for this Phase II study that examined the clinical efficacy and safety of Enz with Dut/Fin in men > 65 years with HNSPCa. Methods: Eligible patients were > 65 years (y) ; at a high risk of AE from ADT by comprehensive geriatric assessment or treating physicians; had metastatic (M1) or biochemical recurrent (M0) HNSPCa with a PSA doubling time < 9 months; and had T > 50ng/dl. They received Enz (160mg daily) and Dut (0.5mg daily) or Fin (5mg daily) until disease progression according to the Prostate Cancer Working Group 2 guidelines. The primary study endpoint is time to PSA progression. The secondary endpoints are time to PSA nadir and treatment-related AEs. Results: As of July 31, 2016, 24 patients were screened (3 ineligible) and 21 were enrolled with a median follow-up of 31 weeks (7-79). Median age at enrollment was 79.5 y (66-94) and 14 %, 72% and 14% had ECOG performance status of 0, 1, and 2, respectively. 57% (n = 12) had M0 and 43% (n = 9) had M1 HNSPCa, with 18%, 62%, 5%, and 10% having Gleason 6, 7, 8, and 9 disease, respectively (5% with unkown Gleason sum). The median PSA at enrollment was 12 ng/ml (2-102). The median time to 90% PSA decline after treatment initiation was 7 weeks (7-20) and 92% achieved 80% DHT decline in 9 months. At the time of analysis, all patients had ongoing PSA decline of > 90% without radiographic evidence of disease progression. Common Grade 1 AEs included gynecomastia (28%), fatigue (28%), hot flashes (19%) and paresthesias (15%). One patient withdrew from the study due to Grade 2 paresthesia. None had Grade 3 or 4 treatment-related AEs. One patient died due to colitis unrelated to study treatments. Conclusions: Enz with Dut/Fin appears to have clinical activity for older patients with M0 and M1 HNSPCa with acceptable side effects. Clinical trial information: NCT02213107