Effectiveness and safety of “real” concurrent stereotactic radiotherapy and immunotherapy in metastatic solid tumors: a systematic review

Background: in the setting of metastatic malignancies, the role of concurrent stereotactic radiosurgery (SRS)/stereotactic radiotherapy (SRT) and immune-checkpoint inhibitors (ICI) is increasing. Few data are available about effectiveness and safety of this strategy. Methods: we used the PRISMA guidelines to perform a systematic review. We selected only articles reporting a “real” concurrent treatment, defined as SRS/SRT performed within 30 days of ICI administration. Results: Despite several limits due to the heterogeneity and retrospective nature of the studies, 1-year local control for brain lesions ranged from 42 to 100% and 1-year regional brain control ranged from 31 to 83%. An interesting rate of local and distant control was reported for concurrent SBRT-ICI on extra-cranial lesions. No relevant signals about toxicity emerged. Conclusions: Based on published evidence, concurrent SRS/SRT and ICI seems to lead intriguing outcomes, without increasing toxicity. Further investigations are warranted to obtain stronger prospective evidence.