PD-1/ PD-l1 Inhibitors and Stereotactic Radiosurgery for Brain Metastases: a systematic review and meta-analysis

Stereotactic radiosurgery (SRS) is the treatment of choice for limited brain metastases (BM), and its combination with PD-1/PD-L1 inhibitors is hypothesized to offer synergistic therapeutic benefits. However, there are concerns regarding augmented risk of radiation-induced brain necrosis (RIBN). This systematic review and meta-analysis evaluate the efficacy and toxicity profile of PD-1/PD-L1 inhibitors combined with SRS or fractionated stereotactic radiotherapy (FSRT).

Four databases were screened, Embase, Web of Science, PubMed and Scopus from inception to November 2025. Primary outcomes were overall survival (OS), extracranial and distant intracranial progression free survival (PFS), and local control (LC). A subgroup analysis was performed based on the primary metastasis origin and radiotherapy treatment modalities. We extracted RIBN events and grade ≥ 3 neurological events. A single-arm meta-analysis was performed using the random-effects modeling. This review protocol was registered on November 2025 on PROSPERO (ID CRD420251171879).