For patients with metastatic non–small cell lung cancer (NSCLC) who have disease progression on immunotherapy, adding stereotactic body radiotherapy (SBRT) could improve progression-free survival (PFS), according to investigators.
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Dr. Allison Campbell
Patients with more CD8+ T cells in circulation, and those with higher tumor infiltrating lymphocyte (TIL) scores derived the most benefit from SBRT, lead author Allison Campbell, MD, PhD, of Yale Cancer Center in New Haven, Conn., and colleagues, reported at the annual meeting of the American Society for Radiation Oncology.
“In rare cases, adding radiation to immunotherapy has been shown to result in therapeutic synergy,” Dr. Campbell said. “When we give high-dose radiation to patients on immunotherapy, some tumors that were not targeted by the radiation can shrink, and this is called ‘the abscopal effect.’ ”
The investigators designed the phase 2 trial to determine if the abscopal effect would occur if high-dose radiation was delivered to a single site in patients who had progressed on checkpoint inhibitor therapy. Fifty-six patients were enrolled, all with at least two sites of metastatic NSCLC. Of these patients, 6 had already progressed on immunotherapy, while 50 were naive to immunotherapy and began pembrolizumab during the trial, with 16 eventually progressing; collectively, these 22 patients with disease progression were identified as candidates for SBRT. Almost all candidates (21 out of 22) completed SBRT, which was delivered in three or five high-dose fractions. Only one site was treated, while other sites were tracked over time with computed tomography (CT) to assess for the abscopal effect. In addition, blood was analyzed for circulating immune cell composition.
After a median follow-up of 15.2 months, the disease control rate was 57%, with some abscopal responses detected. Two patients (10%) achieved a partial response lasting more than 1 year, and 10 patients (48%) maintained stable disease after SBRT. Although programmed death-ligand 1 (PD-L1) positivity was associated with a trend toward increased PFS, this was not statistically significant. In contrast, TIL score was significantly correlated with PFS; patients with TIL scores of 2-3 had a median PFS of 6.7 months, compared with 2.2 months among those with TIL scores of 1 or less. Similarly, immune-related adverse events predicted outcome, with patients who experienced such events achieving longer median PFS than those who did not (6.5 vs 2.2 months). Furthermore, blood testing revealed that the best responders had more CD8+ killer T cells and fewer CD4+ regulatory T cells in peripheral blood compared with patients who responded poorly.
After Dr. Campbell’s presentation, Benjamin Movsas, MD, chair of radiation oncology at the Henry Ford Cancer Institute in Detroit, offered some expert insight. “[The findings from this study] suggest perhaps that radiation may be able to reinvigorate the immune system,” Dr. Movsas said. “Maybe we can get more mileage out of the immunotherapy with this approach. Could radiation kind of be like an immune vaccine of sorts? There’s a lot of exciting possibilities.”
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Dr. Benjamin Movsas
Dr. Movsas also noted how biomarker findings may be able to guide treatment decisions, highlighting how T cell populations predicted outcomes. “This era of precision medicine is really helping us improve benefits,” he said. “The immune profile really matters.”
The investigators disclosed relationships with Genentech, AstraZeneca, Merck, and others.
SOURCE: Campbell et al. ASTRO 2019. Abstract 74.