ARTO trial: Overall survival analysis from a randomized phase II trial testing the benefit of adding stereotactic body radiotherapy to abiraterone acetate in patients with oligometastatic castrate-resistant prostate cancer.

132 Background: ARTO (NCT03449719) is a multicentre, randomized phase II trial testing the benefit of stereotactic body radiation therapy (SBRT) addition to abiraterone acetate (AA) in oligometastatic Castrate Resistant Prostate Cancer (CRPC) patients. Trial ended in October 2022. Results already showed significant benefit in terms of biochemical response and Progression Free Survival (PFS) in the experimental arm, the trial was positive for its primary endpoint. Here we present an updated overall survival (OS) analysis. Methods: Patients affected by oligometastatic CRPC (< 3 non-visceral metastatic lesions) were enrolled in the trial and randomized 1:1 to receive either AA alone (control arm) or associated with concomitant SBRT on all sites of disease (treatment arm). Kaplan-Meier survival analysis was performed to compare OS in the different arms of treatment. Results: One hundred fifty-seven patients were enrolled in ARTO trial. After a median follow up of 27 months, 29 patients died (9 vs 20 in the experimental vs control arm, respectively). Median OS was not reached in neither of the two arms of treatment, with a non-significant trend in favour of the experimental arm (p=0.07). Conclusions: After an updated follow up analysis, results confirmed good prognosis for this population of oligo-metastatic CRPC patients. First line abiraterone acetate conferred long term OS in a selected cohort of patients affected by oligometastatic disease. A positive, nonsignificant trend was found in favour of experimental arm. Considering the low number of events detected, longer follow up is needed to explore impact of upfront SBRT on OS within this randomized phase II trial. Clinical trial information: NCT03449719 .