Background: Radiotherapy(RT)and long-term androgen deprivation therapy(ADT)is a standard treatment for patients with high-risk prostate cancer.However,the optimal duration of ADT is not yet defined.The purpose of this randomized trial was to compare outcomes between 36 and 18 months of ADT in high-risk prostate cancer treated with RT(PCS Ⅳ trial).Methods: PCS Ⅳ randomized patients with node-negative high-risk prostate cancer(T3-4,PSA >20 ng/ml or Gleason score >7),to pelvic RT(whole pelvis 44 Gy/4 1/2 weeks,prostate 70 Gy/7 weeks)and 36(arm 1)vs 18 months(arm 2)of ADT(neo-adjuvant,concomitant,adjuvant).ADT consisted of bicalutamide 50 mg for one month and goserelin 10.8 mg every three months for 36 vs 18 months.Overall survival was the primary end point.From randomization,overall and cancer-specific survival rates were compared between arms with Kaplan-Meier log rank test and Cox regression.Results: From October 2000 to January 2008,310 patients were randomized to arm 1 and 320 to arm 2.Patients characteristics were well balanced between the two arms(median age 71 years,median PSA 16 ng/ml,median Gleason score 8).Most patients had T2-T3 disease.At a median follow-up of 78 months,80/310 patients(25.8%)in arm 1 and 85/320(26.6%)in arm 2 had died(p=0.829).113 patients died of causes other than prostate cancer.Overall and cancer-specific survival hazard ratios were 1.15(0.85-1.56),p=0.366 and 1.07(0.62-1.84),p=0.819,respectively.5-year overall and disease-specific survival rates were 91.1%(87.9-94.3)vs.86.1%(82.3-90.0),p=0.06 and 96.6%(94.5-98.7)vs.95.3%(92.8-97.7),p=0.427 and 10-year overall and disease-specific survival rates were 61.9%(54.1-69.7)vs.58.6%(49.8-67.4),p=0.275 and 84.1%(77.6-90.6)vs.83.7%(76.3-91.1),p=0.819 for arm 1 and arm 2,respectively.There were no significant differences in the rates of biochemical,regional,or distant failure between arms.Conclusions: With a median follow-up of 6.5 years,our study shows that long-term ADT can be safely reduced from 36 to 18 months without compromising outcomes.Analysis of treatment impact on quality of life is now under review.Source of Funding: AstraZeneca Pharmaceuticals Grant.