Reduced Length of ADT and ARTA With XRT in High-Risk Prostate Cancer (RELAX): A Randomised Controlled Trial

To assess the efficacy of a short, intensified regimen of androgen deprivation therapy (ADT) and androgen receptor-targeted agent (ARTA) with curative-intent external beam radiotherapy (XRT) for high-risk prostate cancer (HRPCa) staged with prostate specific membrane antigen (PSMA) imaging.

The RELAX (Reduced Length of ADT and ARTA with XRT in high-risk prostate cancer) trial is a multicentre, phase II randomised non-inferiority trial comparing 9 months of ADT and 6 months of ARTA against the standard 24-month ADT, with definitive dose-escalated hypofractionated pelvic radiotherapy for PSMA-staged non-metastatic HRPCa. The primary endpoint is 5-year disease-free survival (DFS), defined from randomisation to first biochemical or clinico-radiological recurrence or any-cause death. Secondary endpoints include biochemical failure-free survival, metastasis-free survival, overall survival, testosterone recovery, treatment-related adverse effects, and patient-reported outcomes. Participants are monitored with serial serum PSA and testosterone levels, CTCAE and PRO-CTCAE assessments, and PSMA-PETCT at recurrence. The non-inferiority margin is set at 10% absolute difference from an expected 5-year DFS of 85% in the standard arm, with intention-to-treat analysis. The trial is ethics board approved and funded by institutional intramural grant, and registered on clinicaltrials.gov (NCT06818682).

The planned accrual of 206 participants commenced in February 2025, with nearly a third of enrolment completed till date.

The RELAX trial incorporates contemporary standards of PSMA-based staging, dose-escalated hypofractionated radiotherapy, and ARTA for HRPCa. The results are expected to inform the efficacy of a shorter, intensified androgen suppression strategy against the prevailing standard of long-term ADT for these patients.