Local and distant brain control in melanoma and NSCLC brain metastases with concurrent radiosurgery and immune checkpoint inhibition

Introduction: The treatment of brain metastases with stereotactic radiosurgery (SRS) in combination with immune checkpoint inhibitors (ICI) has become more common in recent years, but there is a lack of prospective data on cancer control outcomes when these therapies are administered concurrently. Methods: Data were retrospectively reviewed for patients with non-small cell lung cancer (NSCLC) and melanoma brain metastases treated with SRS at a single institution from May 2008 to January 2017. A parametric proportional hazard model is used to detect the effect of concurrent ICI within 30, 60, or 90 days of ICI administration on local control and distant in-brain control. Other patient and lesion characteristics are treated as covariates and adjusted in the regression. A frailty term is added in the baseline hazard to capture the within-patient correlation. Results: We identified 144 patients with 477 total lesions, including 95 NSCLC patients (66.0%), and 49 (34.0%) melanoma patients. On multivariate analysis, concurrent SRS and ICI (SRS within 30 days of ICI administration) was not associated with local control but was associated with distant brain control. When controlling for prior treatment to lesion, number of lesions, and presence of extracranial metastases, patients receiving this combination had a statistically significant decrease in distant brain failure compared to patients that received non-concurrent ICI or no ICI (HR 0.15; 95% CI 0.05–0.47, p = 0.0011). Conclusion: Concurrent ICI can enhance the efficacy of SRS. Prospective studies would allow for stronger evidence to support the impact of concurrent SRS and ICI on disease outcomes.