Hoped-for results, with a few caveats
Approached for comment on the new findings, Clifford Robinson, MD, professor of radiation oncology, chief of SBRT service, and director of clinical trials and informatics at Washington University, St. Louis, said the results tie in with previous findings.
There are multiple published or presented prospective randomized phase 2 and 3 trials in various disease sites that have explored the role of local therapy, including SBRT, for patients who present with oligometastatic disease.
“These studies have nearly uniformly shown improvements in progression-free and/or overall survival with the inclusion of local therapy,” he told this news organization. Dr. Robinson was not involved with the study.
He explained that relatively few patients present with oligometastatic disease. However, many patients present with more advanced disease, but after an initial course of systemic therapy, develop oligoprogression.
“There is tremendous appeal to using local therapy at the time of oligoprogression in lieu of switching systemic therapy,” said Dr. Robinson. “It allows patients to stay on systemic therapy that is otherwise effective for the remainder of their disease.”
First-line systemic therapies are the most effective and the most tolerable, he continued, and switching systemic therapy introduces the potential for more toxicity and less efficacy. Therefore, it has become increasingly popular to offer SBRT to one or a few sites of oligoprogressive disease based on the results of oligometastatic disease.
“However, there is no established prospective data to guide this practice,” he said. “This trial is the first to examine this carefully in lung and breast cancer patients, and this trial shows what we hoped to see – that use of SBRT after oligoprogression results in improved progression-free survival as compared with standard of care alone. And this was accomplished with limited toxicity.”
There are a few caveats, though, he pointed out. “Progression-free survival is defined as time to first progression or death,” he said. “Since we don’t know what the overall survival is in this abstract, it’s entirely possible that patients live for the same length of time, but just take longer to progress.”
Another caveat is that this was a planned interim analysis. “Typically, planned interim analyses occur to see if the trial should be stopped or to adjust the study based on results,” he said. “It’s unclear what the investigators will do with this information.”
“But overall, these are very exciting data and lend support to the increasingly common practice of treating oligoprogressive disease,” Dr. Robinson added. “Since most of the serious adverse events of SBRT occur later, longer follow-up is needed, although the median survival of patients may not reach that timepoint.”
“For now, practice should not be altered based on these interim results,” he added.
Dr. Tsai reported acting as a consultant/advisor for Varian and Galera and also receiving research funding from Varian. Dr. Robinson reports stock/ownership in Radialogica, acting as a consultant/advisor for Varian, AstraZeneca, EMD Serono, Quantitative Radiology Solutions, research funding from Varian and Merck, and owning patents on systems for cardiac arrhythmias and ablation.
A version of this article first appeared on Medscape.com.
