ARTO trial (NCT03449719): Long-term overall survival analysis from a randomized phase II trial testing the benefit of stereotactic body radiotherapy addition to abiraterone acetate in oligometastatic castrate resistant prostate cancer patients.

151 Background: ARTO (NCT03449719) is a multicentre, randomized phase II trial testing the benefit of stereotactic body radiation therapy (SBRT) addition on top of abiraterone acetate (AA) and androgen deprivation therapy (ADT) in first line Oligometastatic Castrate Resistant Prostate Cancer (omCRPC) patients. Results already showed significant benefit in favour of the experimental arm in terms of biochemical progression free survival (bPFS) and radiological PFS (rPFS) after a median follow up of 24.9 months. Here we present an updated analysis comprehensive of long-term overall survival (OS) and prostate cancer specific survival (PCSS) data. Methods: Patients affected by omCRPC (≤ 3 non-visceral metastatic lesions) were randomized 1:1 to receive either AA+ADT alone (control arm) or the same systemic treatment associated with SBRT on all sites of disease (treatment arm). No previous treatment for mCRPC was allowed. Cox regression analysis was performed to compare bPFS, rPFS, OS and pCSS in the different arms of treatment. Results: One hundred fifty-seven patients were enrolled in ARTO trial. After a median follow up of 53 months (IQR 43-60), 103 bPFS events were recorded (41 vs 62 in the experimental vs control arm, respectively), 100 rPFS events occurred (40 vs 60 in the experimental vs control arm, respectively) and 65 patients died (24 vs 41 in the experimental vs control arm, respectively). Significant benefit in terms of bPFS and rPFS in favour of the experimental arm was confirmed (43 vs 17 months, HR 0.49, 95% CI 0.33-0.73, p 2 lesions) (HR 0.54, 95%CI 0.36-0.81, p=0.003, HR 0.53, 95%CI 0.35-0.81, p=0.003, HR 0.6, 95%CI 0.36-0.99, p=0.04, HR 0.43, 95%CI 0.2-0.9, p=0.02 for bPFS, rPFS, OS and PCSS, respectively). No safety concerns emerged, with 64 vs 71 grade 1/2 and 13 vs 22 grade >2 adverse events in the experimental vs control arm, respectively. Conclusions: After more than doubling the median follow up in this updated analysis, a significant OS and PCSS benefit were detected in patients undergoing concomitant SBRT with AA and ADT treatment compared to AA and ADT alone. These results warrant for confirmation in phase III trials. Clinical trial information: NCT03449719 .