Stereotactic Body Radiotherapy with Immune Checkpoint Inhibitors Ineffective as Treatment for Solid Tumors

A phase 2 clinical trial determined that combining stereotactic body radiotherapy (SBRT) with immune checkpoint inhibitors (ICIs) was not an effective treatment for patients with advanced solid tumors.

According to a study published in JAMA Network Open, the randomized clinical trial, CHEERS, established that the combination of SBRT and ICI monotherapy did not significantly improve progression-free survival (PFS, the period during and after treatment of cancer when the disease does not get worse) or overall survival (OS, the period from diagnosis or treatment where patients are still alive).

The authors of the study noted that the use of SBRT was a safe and effective treatment for patients with limited metastatic diseases, in which SBRT could neutralize active tumor sites without threats of toxicity.

In the study, 96 participants were randomized into two groups: control and experimental. Fifty-one patients were placed in the control group that received only ICIs. The experimental group of 45 patients received a combination of SBRT and ICIs.

Of note, patients in this study had locally advanced or metastatic melanoma, urothelial carcinoma, renal cell carcinoma, non-small cell lung carcinoma, or head and neck squamous cell carcinoma.

The median PFS was 2.8 months for the control group and 4.4 months for the experimental group. The median OS was 11 months and 14.3 months in the control and experimental groups, respectively.

More than half of the patients in the experimental group who fully received the study-prescribed radiotherapy also received SBRT to more than one tumor site. “In doing so, we were able to confirm that targeting multiple disease sites with immunoradiotherapy remains safe, even when both modalities are administered concurrently,” said the authors.

Related to side effects, the authors found that acute treatment-related toxic effects of any grade occurred in 79% of patients and grade 3 or 4 toxic effects occurred in 18% of patients in the control group. As for the experimental group, 78% of patients experienced toxic effects of any grade and 18% of patients experienced grade 3 or 4 toxic effects. There were no reports of grade 5 toxic effects, according to the authors. Common adverse reactions the authors found among patients was fatigue and pruritus (itchiness).

Overall, the authors of the study concluded that the combination of SBRT and ICIs for patients with advanced solid tumors did not provide significant results that were clinically meaningful. Although the combination of SBRT and ICIs was deemed safe, according to the authors, it did not show signs of further improvement for patients. Regarding the PFS and OS among both groups of participants, the authors acknowledged that there were only slight differences. The median PFS and OS for the experimental group did slightly exceed the median PFS and OS for the control group, as the authors emphasized. However, the authors determined that these differences in results were not “statistically significant.”

Still, the authors recognized that there were limitations that could have impacted their research. An important limitation they perceived was that more than half of the patients within the control group had received forms of radiotherapy prior to being included in the CHEERS trial. “This may have resulted in an underestimation of the overall benefit of the experimental treatment,” the authors said. “A heavily pretreated patient population might also offer an explanation for the lower-than-anticipated median PFS in the control (group).”

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