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5001 Background: RT is the standard salvage treatment after RP. The role of HT is not formally demonstrated to date. This trial assessed the efficacy of RT alone vs RT+HT in terms of progression-free survival (PFS), metastase-free survival (MFS) and overall survival (OS) in patients with biological relapse (BR) after RP. After a median follow-up (FU) duration of 5.3 years, we previously reported [Carrie C, Lancet Oncol 2016] a benefit in PFS (80% vs 62% PFS free at 5 years; p < 0.0001) in the combined arm, whatever the risk subgroups. Methods: Patients (pts) were randomized (1:1) to RT alone or RT+HT (goserelin, for 6 months). The randomization was stratified according to radiotherapy modality and risk group. Low risk was defined as Gleason score < 8, surgical margins+, psa doubling time > 8 months and no seminal vesicle involment. Assuming a 45% 5-year PFS of 45% in the RT arm, the trial required 369 pts per arm to detect an improvement of 12% on PFS in RT+HT arm (90% power and 5% bilateral alpha risk), possibly translating into a 10% gain in OS (75% to 85% with 80% power). Biological relapse (BR) was defined according to ASTRO-consensus. Results: At the time of data cutoff (March 2019), the median duration follow-up was 112 months. We confirm the benefit of RT+HT on PFS (HR = 0.54 [CI95% = 0.43-0.68] ; p < 0.0001) whatever the risk subgroup (HR = 0.47 [CI95% = 0.28-0.80] and 0.56 [CI95% = 0.44-0.73] for low and high risk patients, respectively. Metastatic free survival (MFS) is significantly improved in the combined arm (HR = 0.73 [CI95% = 0.54-0.98] ; p = 0.034) with 69% [CI95% = 63-74] versus 75% [CI95% = 70-80] of MFS at 10 years for RT alone and RT+HT, respectively. Conclusions: Salvage radiotherapy combined with short term HT significantly improved 10-years metastatic free survival compared with salvage radiotherapy alone. GETUG-16 considered in the context of previously published results from RTOG-9601, confirm that this strategy can be considered as the new standard for salvage treatment after radical prostatectomy. Clinical trial information: NCT00423475.

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