Objectives Brain metastases (BM) are more common due to improved survival from solid organ cancers. Immunotherapy is a promising treatment but little is known about the intracranial effects and there are no predictive biomarkers of response.

Design We examined a prospective database of BM patients to compare those treated with surgery and immunotherapy versus surgery and standard adjuvant therapy.

Subjects We identified 51 adult patients over 12 months operated for BM.

Methods Outcomes of 7 patients treated with surgery and immunotherapy were compared with matched controls, as well as examining the timing of surgery, radiation therapy and immunotherapy.

Results Patients received ipilimumab or pembrolizumab alone or in combination. Median overall survival was greater in the group receiving immunotherapy (44 months vs. 14 months) despite no significant difference in primary, age or RPA score but there was no difference in intracranial progression. One patient with melanoma receiving ipilimumab prior to surgery underwent supra-marginal resection and peritumoral tissue showed growth pattern, macrophage and T-cell infiltration were all significantly different compared to matched melanoma cases not pre-treated with immunotherapy.

Conclusions Immunotherapy and surgery have been proposed to act synergistically on BM. Immunotherapy certainly influences the BM microenvironment and prolongs overall survival. A prospective biomarker study is planned to investigate the use of brain imaging as a predictor of systemic response to immunotherapy.