Extended Follow-Up Reveals OS Benefit of SABR in Patients With Oligometastatic Cancers

With longer follow-up, patients with a controlled primary tumor and 1 to 5 oligometastases receiving stereotactic ablative radiotherapy (SABR) had a greater rate of overall survival (OS), according to findings from a phase 2 study (J Clin Oncol. 2020 Jun 2. Epub ahead of print).

“The oligometastatic paradigm hypothesizes that patients with a limited number of metastases may achieve long-term disease control, or even cure, if all sites of disease can be ablated. However, long-term randomized data that test this paradigm are lacking,” wrote David A. Palma, MD, PhD, London Health Sciences Centre, Ontario, Canada, and colleagues.

Between 2012 and 2016, Dr Palma et al enrolled 99 patients with a controlled primary malignancy and 1 to 5 metastatic lesions from 10 international centers. Breast (n = 18), lung (n = 18), colorectal (n = 18), and prostate (n = 16) were the most common primary tumor types.

These patients were stratified based on the number of metastases (1-3 v 4-5) and randomized in a 1:2 ratio to receive palliative standard-of-care treatments (arm 1) or standard care plus SABR (arm 2).

The primary end point of the study was OS (using an α of .20, wherein P <.20 indicates a positive trial), and secondary end points included progression-free survival (PFS), toxicity, and quality of life (QOL).

Follow-up lasted for a median of 51 months. The 5-year OS rates were 17.7% (95% CI, 6%-34%) versus 42.3% (95% CI, 28%-56%) for arms 1 and 2, respectively (stratified log-rank P = .006). The 5-year PFS rates were not reached (3.2%; 95% CI, 0%-14% at 4 years with last patient censored) and 17.3% (95% CI, 8%-30%), respectively (P = .001).

No new grade 2-5 adverse events were reported, and no differences in QOL were observed between the treatment arms.

“With extended follow-up, the impact of SABR on OS was larger in magnitude than in the initial analysis and durable over time,” Dr Palma and colleagues wrote.

“There were no new safety signals, and SABR had no detrimental impact on QOL,” they concluded.—Hina M. Porcelli