While the combination of stereotactic radiosurgery (SRS) and immune checkpoint inhibitors (ICI) is becoming more widely used in the treatment of brain metastases (BM), there is a paucity of prospective data to validate both the safety and efficacy, as well as the optimal timing of these two therapies relative to one another.

A PICOS/PRISMA/MOOSE selection protocol was used to identify 17 studies across 15 institutions in 3 countries. Inclusion criteria were patients: diagnosed with BM; treated with SRS/ICI, either concurrently or non-concurrently; with at least one of the primary or secondary outcome measures reported. Weighted random effects meta-analyses using the DerSimonian and Laird method were performed. The primary outcome was 1-year overall survival (OS). Secondary outcomes were 1-year local control (LC), 1-year regional brain control (RBC), and radionecrosis incidence.

A total of 534 patients with 1,570 BM were included. The 1-year OS was 64.6% and 51.6% for concurrent and non-concurrent therapy, respectively (p < 0.001). Local control at 1-year was 89.2% and 67.8% for concurrent and non-concurrent therapy, respectively (p = 0.09). The RBC at 1-year was 38.1% and 12.3% for concurrent and ICI administration prior to SRS, respectively (p = 0.049). The overall incidence of radionecrosis for all studies was 5.3%.

Concurrent administration of SRS/ICI may be associated with improved safety and efficacy versus sequential therapy. These findings, however, are hypothesis-generating and require further validation by ongoing and planned prospective trials.