As reported in JAMA Oncology by Olson et al, the primary toxicity results of the phase II SABR-5 trial have shown a low rate of toxic effects with stereotactic ablative radiotherapy (SABR) for patients with up to five oligometastases.
As stated by the investigators: “After the publication of the landmark SABR-COMET trial, concerns arose regarding high-grade toxic effects of treatment with SABR for oligometastases…. [The] trial demonstrated a promising survival advantage to SABR but a concerning rate of high-grade toxic effects (28.8% for grade 2 or higher, 4.5% for grade 5).”
The study included 381 patients undergoing SABR for up to five oligometastases across all six cancer centers in British Columbia between November 2016 and July 2020. As noted by the investigators, during this period, patients were only eligible to receive SABR in these settings in trials within British Columbia, with the analysis thus being based on population.
The most common diagnoses were prostate cancer (n = 123, 32%), colorectal cancer (n = 63, 17%), breast cancer (n = 42, 11%), and lung cancer (n = 33, 9%). The number of SABR-treated sites were one in 263 patients (69%), two in 82 (22%), and at least three in 36 (10%); the most common sites of treatment were the lungs (n = 188, 34%), nonspine bone (n = 136, 25%), spine (n = 85, 16%), lymph nodes (n = 78, 14%), liver (n = 29, 5%), and adrenal glands (n = 15, 3%).
Median follow-up was 25 months (range = 1–54 months).
Based on the highest-grade toxic effect per patient, grade 2 toxicity occurred in 14.2% of patients (95% confidence interval [CI] = 10.7%–17.7%), grade 3 occurred in 4.2% (95% CI = 2.2%–6.2%), grade 4 occurred in 0%, and grade 5 occurred in 0.3% (95% CI = 0%–0.8%). The rate of grade ≥ 2 toxicity was 18.6% (95% CI = 14.7%–22.5%).
On Kaplan-Meier analysis, the cumulative incidence of SABR-associated toxicity at 2 years was 8% for grade ≥ 2 effects and 4% for grade ≥ 3 effects.
The investigators concluded: “This single-arm, phase II clinical trial found that the incidence of grade 3 or higher SABR toxic effects in this population-based study was less than 5%. Furthermore, the rates of grade 2 or higher toxic effects (18.6%) were lower than previously published for SABR-COMET (29%). These results suggest that SABR treatment for oligometastases has acceptable rates of toxic effects and potentially support further enrollment in randomized phase III clinical trials.”
Disclosure: The study was supported by a grant from the BC Cancer Agency. For full disclosures of the study authors, visit jamanetwork.com.The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.