To characterize the effect of concurrent stereotactic radiosurgery-stereotactic radiation therapy (SRS-SRT) and immune checkpoint inhibitors on patient outcomes and safety in patients with brain metastases (BMs).

We retrospectively identified metastatic non-small cell lung cancer, melanoma, and renal cell carcinoma patients who had BMs treated with SRS-SRT from 2010 to 2016 without prior whole-brain radiation therapy. We included SRS-SRT patients who were treated with anti-cytotoxic T-lymphocyte-associated protein 4 (ipilimumab) and anti-programmed cell death protein 1 receptor (nivolumab, pembrolizumab). Patients who were given immune checkpoint inhibitors on active or unreported clinical trials were excluded, and concurrent immune checkpoint inhibition (ICI) was defined as ICI given within 2 weeks of SRS-SRT. Patients were managed with SRS-SRT, SRS-SRT with nonconcurrent ICI, or SRS-SRT with concurrent ICI. Progression-free survival and overall survival (OS) were estimated using Kaplan-Meier survival curves, and Cox proportional hazards models were used for multivariate analysis. Logistic regression was used to identify predictors of acute neurologic toxicity, immune-related adverse events, and new BMs.

A total of 260 patients were treated with SRS-SRT to 623 BMs. Of these patients, 181 were treated with SRS-SRT alone, whereas 79 received SRS-SRT and ICI, 35% of whom were treated with concurrent SRS-SRT and ICI. Concurrent ICI was not associated with increased rates of immune-related adverse events or acute neurologic toxicity and predicted for a decreased likelihood of the development of ≥3 new BMs after SRS-SRT (P=.045; odds ratio, 0.337). Median OS for patients treated with SRS-SRT, SRS-SRT with nonconcurrent ICI, and SRS-SRT with concurrent ICI was 12.9 months, 14.5 months, and 24.7 months, respectively. SRS-SRT with concurrent ICI was associated with improved OS compared with SRS-SRT alone (P=.002; hazard ratio [HR], 2.69) and compared with nonconcurrent SRS-SRT and ICI (P=.006; HR, 2.40) on multivariate analysis. The OS benefit of concurrent SRS-SRT and ICI was significant in comparison with patients treated with SRS-SRT before ICI (P=.002; HR, 3.82) or after ICI (P=.021; HR, 2.64).

Delivering SRS-SRT with concurrent ICI may be associated with a decreased incidence of new BMs and favorable survival outcomes without increased rates of adverse events.