ADT with SBRT versus SBRT alone for hormone-sensitive oligorecurrent prostate cancer (RADIOSA): a randomised, open-label, phase 2 clinical trial.

Background: Metastasis-directed therapy by stereotactic body radiotherapy (SBRT) has been shown to improve clinical outcomes in the oligometastatic prostate cancer setting. We aimed to investigate whether short-course androgen deprivation therapy (ADT) and SBRT at all oligometastatic sites versus SBRT alone improves clinical progression-free survival in men with metachronous oligorecurrent hormone-sensitive prostate cancer.

Methods: The RADIOSA study was a single-centre, randomised, open-label, controlled phase 2 trial done in the European Institute of Oncology, IRCCS, Milan, Italy. Key eligibility criteria were histologically proven initial diagnosis of adenocarcinoma of the prostate, biochemical progression after radical local prostate treatment, nodal relapse in the pelvis, extra-regional nodal relapse, bone metastases at next-generation imaging with a maximum of three lesions, Eastern Cooperative Oncology Group (ECOG) performance status 0-1, and age 18 years or older. Participants were stratified according to prostate-specific membrane antigen doubling time (≤3 vs >3 months), metastases localisation (node vs bone), and diagnostic imaging (positron emission tomography vs MRI) and were randomly assigned (1:1) using a computer-generated random number to SBRT alone or SBRT in combination with 6 months of ADT. For SBRT treatment, a schedule of 30 Gy in three fractions every other day (with the equivalent dose in 2 Gy fractions being 98·6 Gy, considering α/β ratio of 1·5 Gy and biologically effective dose of >100 Gy), or equivalent regimens depending on disease site location, was administered. Patients in the SBRT with ADT group received 6 months of ADT with a luteinising hormone-releasing hormone analogue within 1 week before the start of SBRT. The allocated treatment was not masked. The primary outcome measure was clinical progression-free survival. All analyses followed a modified intention-to-treat principle, consisting of all patients assigned to a treatment group who had available data. The trial is registered at ClinicalTrials.gov, NCT02680587, and is complete.

Findings: Between Aug 1, 2019, and April 30, 2023, 218 patients were assessed for eligibility, 113 were excluded, and 105 were enrolled and randomly assigned to an intervention (52 to SBRT only and 53 to SBRT with ADT). Three patients were lost to follow-up and 51 patients in each group were assessed for the primary outcome. The median age at study enrolment was 70 years (IQR 65-75); data on race and ethnicity were not collected. With a median follow-up of 31 months (IQR 16-36) for both groups, the median clinical progression-free survival was 15·1 months (95% CI 12·4-22·8) for the SBRT group versus 32·2 months (22·4-not reached) for the SBRT with ADT group (hazard ratio 0·43 [95% CI 0·26-0·72], p=0·0010]). One gastrointestinal grade 1 adverse event (SBRT group) and one genitourinary grade 3 adverse event (left ureter stenosis, SBRT with ADT group) were reported, with no late toxicities observed. 22 grade 1 ADT-related adverse events were reported, all of which had resolved at the last follow-up. No treatment-related deaths were recorded.

Interpretation: To our knowledge, the RADIOSA trial represents the first randomised trial in the metachronous oligometastatic hormone-sensitive prostate cancer setting to report improved clinical progression-free survival with the combination of SBRT and a short course of ADT, although carefully selected patients might still benefit from SBRT alone. By demonstrating improved clinical progression-free survival, the RADIOSA trial reinforces the role of metastasis-directed therapy in delaying systemic treatment escalation. Additionally, it underscores the need for further studies to determine the optimal duration of ADT and identify biomarkers predicting response to SBRT alone.

Funding: Italian Association of Cancer Research.