Real-world data support efficacy of SABR for extracranial oligometastases
medwireNews: The beneficial survival outcomes and low toxicity associated with stereotactic ablative body radiotherapy (SABR) in patients with extracranial oligometastases persist in the real-world setting.
“The study findings complement existing evidence from a randomised, phase 2 trial, and represent high-level, real-world evidence supporting the use of SABR in this patient cohort, with a phase 3 randomised, controlled trial to confirm these findings underway,” say the researchers in The Lancet Oncology.
The authors of an accompanying commentary note that “[w]hile we await phase 3 data, we must appreciate the practical dilemma that for most patients, no trial is available.”
Rohann Correa and David Palma (both from London Health Sciences Centre in Ontario, Canada) therefore write: “[I]n the absence of a trial and in consideration of all available data, we propose that well selected patients with one to three metachronous oligometastases and a controlled primary tumour should be offered ablative therapy, and that SABR is the ablative therapy with the most robust supporting evidence.”
The study included 1422 patients with 1–3 metachronous extracranial oligometastases and a definitively treated primary tumor; the majority (75.6%) had one oligometastasis, 19.6% had two, and 4.8% had three. The most common primary tumor was prostate cancer (28.6%), followed by colorectal (27.9%), renal (10.1%), breast (5.5%), and lung (4.5%) cancer.
Patients received 3–8 SABR fractions at a dose of 24–60 Gy across 17 NHS radiotherapy centers in England between 2015 and 2019, and were followed up for a median of 13 months. The most frequently treated oligometastatic sites were the lymph nodes (31.3%), lungs (29.3%), and bones (12.0%).
The 1- and 2-year OS rates were 92.3% and 79.2%, respectively, and varied according to primary tumor site; the 2-year OS rates ranged from 60.5% in patients with melanoma to 94.6% for those with prostate cancer.
The findings were similar in a sensitivity analysis restricted to participants with a follow-up of more than 18 months, with a 1-year OS rate of 89.0% and a 2-year rate of 75.8%.
Among the 1137 patients with available local control outcomes, 19.9% had a local progression event, and the 1- and 2-year local control rates were 86.9% and 72.3%, respectively. The local control rates also differed by primary tumor type, ranging from 2-year rates of 59.3% in patients with rectal cancer to 83.6% in those with lung cancer.
New metastases occurred in 30.7% of the 1139 patients with evaluable data. The 1- and 2-year metastasis-free survival rates were 84.0% and 52.0%, respectively, and again varied by tumor type, ranging from 40.0% for prostate cancer to 73.1% for lung cancer.
Anastasia Chalkidou (King’s College London, UK) and co-authors emphasize that alongside the “excellent clinical outcomes” in their study, SABR was also associated with “low rates of treatment-related toxicity.”
Indeed, the most common grade 3 adverse event was fatigue, occurring in 2% of patients, and the most frequent grade 4 event was liver enzyme elevations, which occurred in 1% of patients, and there were no adverse event-related deaths reported.
Chalkidou et al note that “minimal changes in quality-of-life outcomes” were reported over time, as measured by the 3-level version of the Euroqol 5D questionnaire. This “correlates with the low rates of adverse events observed, and suggests that patients tolerated SABR well, in contrast with other, normally challenging radiotherapy courses,” they conclude.
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