SBRT on Oligoprogressive Lesions: Benefit in Lung Cancer

Roxanne Nelson, RN, BSN

October 26, 2021

CHICAGO — Stereotactic body radiation therapy (SBRT) directed at progressive lesions in patients with oligoprogressive metastatic non-small cell lung cancer (NSCLC) was beneficial and significantly improved progression-free survival (PFS), suggest clinical trial results presented this week.

Patients treated with SBRT had a median PFS of 44 weeks, compared with 9 weeks for those who received standard care.

However, no benefit was observed in patients with metastatic breast cancer. There was no significant difference in PFS between the two groups (18 weeks with SBRT vs 19 weeks with standard care).

"In this pre-planned interim analysis, we demonstrated the benefit of SBRT to sites of oligoprogression on overall progression-free survival, which was the primary endpoint," said lead author C. Jillian Tsai, MD, PhD, a radiation oncologist and director of metastatic disease radiation oncology research at Memorial Sloan Kettering Cancer Center in New York City. "The difference was driven by the substantial response in [this] NSCLC cohort."

There was no benefit of SBRT seen in the breast cohort, she noted, and most breast patients developed new lesions upon further progression.

Tsai and colleagues are planning to close the trial early, after the interim analysis established the benefit of SBRT. They are now investigating why SBRT was beneficial in NSCLC but not in breast cancer.

The findings were presented here at the American Society for Radiation Oncology (ASTRO) annual meeting.

Tsai explained that the current standard of care for patients with oligoprogressive metastatic NSCLC is to switch to a different targeted therapy or chemotherapy following progression, but options may be limited. Efficacy for second-line therapy can be poor, with PFS ranging from about 4 months to 10 months for NSCLC, "and after second line, efficacy for third and fourth lines is even poorer," she said.

Similarly, for breast cancer, PFS ranges from about 9 months to 20 months for estrogen-receptor positive patients. "But for triple negative patients, there really is no standard of care and PFS is poor," Tsai said.

SBRT Superior to Standard of Care

The authors hypothesized that there is an oligoprogressive state in metastatic cancer, in which disease control can be improved by applying local therapy to progressive lesions only..

The cohort included 102 patients with metastatic NSCLC or breast cancer who had received one or more lines of systemic therapy and had oligoprogressive lesions amenable to SBRT. There was no upper limit of nonprogressive lesions.

Oligoprogression was defined as Response Evaluation or Positron Emission Tomography Response Criteria in Solid Tumors documented progression ≤ 5 individual lesions.

Patients were randomly assigned to receive either SBRT to all progressive sites plus palliative standard of care or systemic SOC only. Systemic therapy was per physician's discretion.

There were 58 patients with NSCLC (30 in the SBRT group) and 44 patients with breast cancer (22 in each group).

Most patients (75%) had more than one site of oligoprogression and 47% had more than 5 total metastatic lesions. About half of patients (54%) had received immunotherapy and the majority of those with NSCLC (86%) did not harbor an actionable driver mutation. About one third (32%) of the breast cancer cohort were triple negative.

Patients were followed for a median of 45 weeks (58 weeks for living patients), by which time 78 (74%) had experienced further tumor progression and 39 (37%) had died.

Median progression-free survival for the entire cohort was 31 weeks for SBRT and 11 weeks for palliative SOC (P = .002).

In multivariable analysis that stratified for factors including age, sex, lines of systemic therapy, and change of systemic therapy, the progression-free survival benefit of SBRT continued to remain substantial in the NSCLC cohort (hazard ratio: 0.38; P = .007).

Adverse events were higher in the SBRT group. Grade 2 or higher adverse events occurred in 23 (61%) of SBRT patients, and 15 (40%) of SOC patients (P = .13).

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, Missouri, 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 Medscape Medical News. 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 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 they 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," 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.

Tsai reported acting as a c onsultant/advisor for Varian and Galera, and also receiving research funding from Varian. Robinson reports stock/ownership in R adialogica, 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.

American Society for Radiation Oncology (ASTRO) annual meeting: Abstract LBA-3. Presented October 24, 2021.

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