medwireNews: Patients with oligometastatic castration-resistant prostate cancer (CRPC) benefit from the addition of stereotactic body radiotherapy (SBRT) to first-line abiraterone acetate plus prednisone (AAP), show phase 2 trial results.
The primary endpoint of biochemical response as well as the secondary endpoints of complete biochemical response and progression-free survival (PFS) were significantly improved with the use of SBRT, reports the research team in the Journal of Clinical Oncology.
The investigators add that the addition of SBRT did not lead to “any meaningful” increase in the incidence of adverse events (AEs) and they therefore believe that “[p]hase III trials are warranted to test survival end points in larger cohorts.”
The ARTO trial included 157 patients who had not received prior systemic treatment for metastatic CRPC and had no more than three bone or nodal metastatic lesions (patients with visceral lesions were excluded). All participants received abiraterone at a daily dose of 1000 mg alongside prednisone 5 mg twice a day as well as concomitant androgen deprivation therapy, with those randomly assigned to the experimental arm additionally receiving at least 100 Gy SBRT across all sites of metastatic disease.
At the 6-month mark, a biochemical response – defined as a decrease in prostate-specific antigen (PSA) levels from baseline of at least 50% – was achieved by 92.0% of the 75 patients who received SBRT plus AAP and 68.3% of the 82 given AAP alone. The between-group difference was significant and equated to an odds ratio (OR) of 5.34 in favor of add-on SBRT.
The rate of complete biochemical response (PSA ≤0.2 ng/mL) at 6 months was similarly significantly higher in the SBRT than control arm, at 56.0% versus 23.3%, and an OR of 4.22.
And PFS was also significantly prolonged with the addition of SBRT to AAP, with the median unreached versus 17 months with AAP alone, giving a hazard ratio (HR) for progression or death of 0.35.
The median overall survival was not reached in either treatment group, but the HR for death was 0.65, “with a nonsignificant trend in favor of the experimental versus control arm,” say Giulio Francolini (Azienda Ospedaliero Universitaria Careggi, Florence, Italy) and co-authors.
They note that at the time of analysis, patients had been followed up for a median of 24.9 months, and therefore “these data may require more time to mature, especially given the good prognosis of the population studied (oligometastatic patients without visceral metastases).”
AEs of grade 3 or higher occurred in 10.6% of patients in the SBRT plus AAP group and 15.8% of those in the AAP alone group, and there was no increase in the incidence of AEs considered potentially related to SBRT in the experimental versus control group, such as any-grade osteoporosis or fracture (2.7 vs 6.0%), hematuria (4.9 vs 5.3%), and gastrointestinal disorders (2.7 vs 1.2%).
Francolini and colleagues note that “the treatment of [metastatic] CRPC is a rapidly evolving landscape,” especially given the promising reports of first-line treatment with PARP inhibitors and the use of androgen receptor-targeted agents in the metastatic hormone-sensitive setting.
They continue: “For this reason, implementation of SBRT in this scenario could be an evolving paradigm, and prospective trials testing different combinations are eagerly needed to provide clinical rationale for SBRT use in oligometastatic prostate cancer.”
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J Clin Oncol 2023; doi:10.1200/JCO.23.00985