Adding SBRT to frontline abiraterone shows benefit in oligometastatic CRPC

The addition of stereotactic body radiation therapy (SBRT) to first-line abiraterone acetate (Zytiga) and prednisone (AAP) produced a clinical benefit in patients with oligometastatic castration-resistant prostate cancer (CRPC), according to findings from the phase 2 ARTO trial (NCT03449719) published in the Journal of Clinical Oncology (JCO).¹

“The ARTO trial suggests that patients treated with concomitant SBRT and abiraterone acetate may have significant advantage in terms of PSA reduction at 6 months and progression-free survival when compared with patients treated with standard systemic treatment alone. These results were obtained without any meaningful signal of increased rate of adverse event,” Michael A. Carducci, MD, associate editor, JCO, wrote in a commentary published along with the manuscript.

Biochemical response (BR) rate, the primary end point of the trial, was 92% in the SBRT plus AAP arm vs 68.3% with AAP alone (odd ratio [OR], 5.34 in favor of the SBRT arm; P = .001). The complete BR rate (CBR) was 56% vs 23.2%, respectively (OR, 4.22; P <.001).

At a median follow-up of 24.9 months, the median progression-free survival was not reached in the SBRT arm compared with 17 months with AAP alone, translating to a 65% reduction in the risk of disease progression or death (HR, 0.35; P < .001).¹

“The ARTO trial suggests that patients treated with concomitant SBRT and abiraterone acetate may have significant advantage in terms of PSA reduction at 6 months and progression-free survival when compared with patients treated with standard systemic treatment alone. These results were obtained without any meaningful signal of increased rate of adverse event,” Michael A. Carducci, MD, associate editor, JCO, wrote in a commentary published along with the manuscript.¹

Overall, 157 patients with oligometastatic CRPC were enrolled in the ARTO trial between January 2019 and September 2022. Patients were randomized to AAP alone (n = 82) or in combination with SBRT (n = 75). The median age across all patients was 74 years and the median baseline PSA was 3.42 ng/ml. About 82% of patients in each arm had ISUP grade >3 disease.

The study design defined the primary end point of BR as a decrease in PSA of ≥50% from baseline detected at 6 months following treatment initiation. Complete BR was defined as having a PSA of <0.2 ng/mL at 6 months following the start of treatment.

Regarding safety, 48 (64%) patients in the SBRT arm experienced grade 1/2 adverse events (AEs) compared with 54 (65.8%) patients in the AAP-alone arm. The rates of grade >2 AEs were 10.6% (n = 8 patients) and 15.8% (n = 13 patients), respectively. According to the study authors, “most toxicities were mild and related to systemic treatment.”¹

“Targeting these sites of disease with SBRT and standard of care agents is safe and feasible, with evolving data from studies like this showing consistency in the benefits to this approach in enhancing response rates measured by PSA as well as lengthening time to radiographic progression. These results should be confirmed in larger studies and placed into context with the changing landscape of treatment options for metastatic hormone sensitive and metastatic castration resistant disease,” wrote Carducci in his commentary.¹

Reference

1. Francolini G, Gaetano Allegra A, Detti B, et al. Stereotactic Body Radiation Therapy and Abiraterone Acetate for Patients Affected by Oligometastatic Castrate-Resistant Prostate Cancer: A Randomized Phase II Trial (ARTO) [published online ahead of print September 21, 2023]. J Clin Oncol. doi: 10.1200/JCO.23.00985