Tolerance and outcomes of stereotactic radiosurgery combined with anti-programmed cell death-1 (pembrolizumab) for melanoma brain metastases

Anti-programmed cell death-1 (anti-PD1) antibodies are currently the first-line treatment for patients with metastatic BRAF wild-type melanoma, alone or combined with the anti-CTLA4 monoclonal antibody, ipilimumab. To date, data on safety and the outcomes of patients treated with the anti-PD1 monoclonal antibodies, pembrolizumab (PB), or nivolumab, combined with stereotactic radiosurgery (SRS), for melanoma brain metastases (MBM) are scarce. We retrospectively reviewed all patients with MBM treated with PB combined with SRS between 2012 and 2015. The primary endpoint was neurotoxicity. The secondary endpoints were local, distant intracranial controls and overall survival (OS). Among 74 patients with MBM treated with SRS, 25 patients with a total of 58 MBM treated with PB combined with SRS within 6 months were included. Radiation necrosis, occurring within a median time of 6.5 months, was observed for four MBM (6.8%) in four patients. No other significant SRS-related adverse event was observed. After a median follow-up of 8.4 months, local control was achieved in 46 (80%) metastases and 17 (68%) patients. Perilesional oedema and intratumour haemorrhage appearing or increasing after SRS were associated with local progression (P<0.001). The median OS was 15.3 months (95% confidence interval: 4.6-26). The timing between SRS and PB administration did not seem to influence the risk of radiation necrosis, intracranial control or OS. SRS combined with PB was well tolerated and achieved local control in 80% of the lesions. Prolonged OS was observed compared with that currently yielded in this population of patients. Prospective studies are required to explore further the optimal ways to combine immunotherapy and SRS.