Stereotactic Body Radiotherapy (SBRT/SABR) to All Disease Sites Plus Abiraterone Acetate and Prednisone for Oligometastatic Castration-Resistant Prostate Cancer: The Randomized Phase II ARTO Trial

Abstract

Purpose: ARTO (ClinicalTrials.gov identifier: NCT03449719) was a multicenter, randomized phase II clinical trial evaluating the benefit of adding stereotactic body radiation therapy (SBRT; stereotactic ablative body radiotherapy) to abiraterone acetate and prednisone (AAP) in patients with oligometastatic castration-resistant prostate cancer (CRPC). Materials and methods: Eligible patients had oligometastatic CRPC, defined as three or fewer nonvisceral metastatic lesions. Patients were randomly assigned 1:1 to AAP alone (control arm) or AAP with concomitant SBRT delivered to all sites of disease (experimental arm). The primary end point was biochemical response (BR), defined as a prostate-specific antigen (PSA) decrease of ≥50% from baseline at 6 months after treatment start. Secondary end points included complete biochemical response (CBR), defined as PSA <0.2 ng/mL at 6 months after treatment, and progression-free survival (PFS). Results: Between January 2019 and September 2022, 157 patients were enrolled. BR occurred in 79.6% of patients overall, including 92% in the experimental arm versus 68.3% in the control arm, with an odds ratio (OR) of 5.34 (95% CI, 2.05 to 13.88; P = .001) favoring SBRT plus AAP. CBR occurred in 38.8% of patients overall, including 56% versus 23.2% in the experimental versus control arm, respectively, with an OR of 4.22 (95% CI, 2.12 to 8.38; P < .001). SBRT significantly improved PFS, with a hazard ratio for progression of 0.35 (95% CI, 0.21 to 0.57; P < .001) for the experimental arm versus the control arm. Conclusion: ARTO met its primary end point for biochemical control and showed improved PFS, supporting a clinical advantage for adding SBRT to first-line AAP in patients with oligometastatic metastatic castration-resistant prostate cancer.