Brain metastasis formation and irradiation by stereotactic radiation therapy combined with immunotherapy: A systematic review

Introduction: Brain metastasis (BM) is a complex process that implies immune cells and microglia. Stereotactic radiation therapy (SRT) and immunotherapy (IT) are established to increase the immune response; but their association has never been prospectively studied. Materials and methods: Two reviewers performed a systematic review in original papers published up to September 2019. We analysed OS, local (mLRF) and regional (mBRF) median disease-free survival in patients with BMs after SRT with and without IT. Results: Upon 14 studies, eleven concerned melanoma, three concerned lung cancers. SRT-IT showed better OS, mLRF and mBRF than SRT. mBRF was better if SRT was performed with short delay from IT. No higher rates of radionecrosis and haemorrhage were found among groups. Conclusion: This review suggests SRT combined to IT in melanoma is safe and could provide better BRF, suggesting a lymphocytic immune reaction in brain. No improvement trend was found in lung cancer BM.