In an Italian phase II trial (ARTO) reported in the Journal of Clinical Oncology, Francolini et al found that the addition of stereotactic body radiation therapy (SBRT) to first-line abiraterone acetate and prednisone resulted in a significantly higher rate of biochemical response among patients with oligometastatic castrate-resistant prostate cancer, as well as improved progression-free survival.
Study Details
In the multicenter trial, 157 patients with three or fewer nonvisceral metastatic lesions were randomly assigned between January 2019 and September 2022 to receive SBRT plus abiraterone acetate and prednisone (n = 75) or abiraterone acetate and prednisone alone (n = 82). Abiraterone acetate and prednisone consisted of abiraterone at 1,000 mg once daily plus prednisone at 5 mg orally twice daily. Patients concurrently received androgen-deprivation therapy with a luteinizing hormone–releasing hormone analog. All SBRT doses and fractionations were permitted, as long as treatment was administered to all sites of disease with a biologically effective dose of ≥ 100 Gy. Patients underwent SBRT 30 days from the date of their first abiraterone acetate and prednisone administration. The primary endpoint was biochemical response defined as prostate-specific antigen (PSA) decrease of ≥ 50% from baseline at 6 months from start of treatment. Secondary endpoints included complete biochemical response defined as PSA < 0.2 ng/mL at 6 months, and progression-free survival.
Key Points
At 6 months, biochemical response was achieved in 92% of the SBRT/abiraterone acetate and prednisone group vs 68.3% of the control group (odds ratio [OR] = 5.34, 95% confidence interval [CI] = 2.05–13.88, P = .001). Complete biochemical response was observed in 56% vs 23.2% of patients (OR = 4.22, 95% CI = 2.12–8.38, P < .001).
Median follow-up was 24.9 months (interquartile range = 17.1–35.8 months). Median progression-free survival was not reached in the SBRT/abiraterone acetate and prednisone group vs 17 months in the control group (HR = 0.35, 95% CI = 0.21–0.57, P < .001). The first progression-free survival event was biochemical progression in 11 vs 25 patients and radiographic progression in 11 vs 28 patients. Median biochemical progression-free survival was not reached vs 36 months (HR = 0.33, 95% CI = 0.16–0.67, P = .002) and median radiographic progression–free survival was not reached vs 34 months (HR = 0.39, 95% CI = 0.19–0.81, P = .011). Median overall survival was not reached in either group. Death occurred in 9 vs 15 patients (HR = 0.65, 95% CI = 0.28–1.49).
Grade ≥ 2 adverse events occurred in 8 patients (10.6%) in the SBRT/abiraterone acetate and prednisone group vs 13 (15.8%) in the control group. The most common events were cardiovascular disorders (4.0%) and hematuria (2.7%) in the SBRT/abiraterone acetate and prednisone group and blood test abnormalities apart from blood count abnormalities (4.9%), lower urinary tract symptoms (3.6%), and cardiovascular disorders (3.6%) in the control group. Osteoporosis or fracture was observed in 2.7% vs 6.0% of patients.
The investigators concluded, “The trial reached its primary endpoint of biochemical control and progression-free survival, suggesting a clinical advantage for SBRT in addition to first-line abiraterone acetate and prednisone treatment in patients with metastatic castration-resistant prostate cancer.”
Giulio Francolini, MD, of the Radiation Oncology Unit, Azienda Ospedaliero Universitaria Careggi, Florence, is the corresponding author for the Journal of Clinical Oncology article.
Disclosure: The study was supported by Janssen Cilag SpA. For full disclosures of the study authors, visit ascopubs.org.
