BACKGROUND: Phase 3 trials have demonstrated a benefit from adjuvant radiation therapy (ART) for men who have adverse factors at radical prostatectomy (RP). However, some patients have a high risk of progression despite ART. The role of systemic therapy with ART in this high-risk group remains to be defined. METHODS: Patients who had either a post-RP prostate-specific antigen (PSA) nadir > 0.2 ng/mL and a Gleason score >/=7 or a PSA nadir /=8, and a pathologic tumor (pT) classification >/= pT3 received 6 months of androgen-deprivation therapy (ADT) plus radiotherapy and 6 cycles of docetaxel. The primary objective was to assess whether the addition of ADT and docetaxel to ART resulted in a freedom from progression (FFP) rate >/= 70% compared with an expected rate of 50%. Multivariate logistic and Cox regression analyses were used to model associations between factors and outcomes. RESULTS: In total, 74 patients were enrolled. The median follow-up was 4.4 years. The pathologic tumor classification was pT2 in 4% of patients, pT3 in 95%, and pT4 in 1%. The Gleason score was 7 in 18% of patients and >/=8 in 82%. Post-RP PSA levels were 0.2 ng/mL in 47%. The 3-year FFP rate was 73% (95% confidence interval, 61%-83%), and the 3-year cumulative incidence of biochemical, distant, and local failure was 26%, 7%, and 0%, respectively. In multivariate models, postprostatectomy PSA nadir was associated with 3-year FFP, Gleason score, and PSA with biochemical failure. Grade 3 and 4 neutropenia was common; however, only 3 episodes of febrile neutropenia occurred. Late toxicities were not impacted by the addition of systemic therapy. CONCLUSIONS: Combined ADT, docetaxel, and ART for men with high-risk prostate cancer after prostatectomy exceeded the prespecified study endpoint of 70% 3-year FFP. Phase 3 trials assessing combined local and systemic therapies for these high-risk patients are warranted. Cancer 2017;123:2489-96. (c) 2017 American Cancer Society.