Immunotherapy of brain metastases: breaking a dogma

Until very few years ago, the oncology community dogmatically excluded any clinical potential for immunotherapy in controlling brain metastases. Therefore, despite the significant therapeutic efficacy of monoclonal antibodies to immune check-point(s) across a wide range of tumor types, patients with brain disease were invariably excluded from clinical trials with these agents. Recent insights on the immune landscape of the central nervous system, as well as of the brain tumor microenvironment, are shedding light on the immune-biology of brain metastases. Interestingly, retrospective analyses, case series, and initial prospective clinical trials have recently investigated the role of different immune check-point inhibitors in brain metastases, reporting a significant clinical activity also in this subset of patients. These findings, and their swift translation in the daily practice, are driving fundamental changes in the clinical management of patients with brain metastases, and raise important neuroradiologic challenges. Along this line, neuro-oncology undoubtedly represents an additional area of active investigation and of growing interest to support medical oncologists in the evaluation of clinical responses of brain metastases to ICI treatment, and in the management of neurologic immune-related adverse events. Aim of this review is to summarize the most recent findings on brain metastases immunobiology, on the evolving scenario of clinical efficacy of ICI therapy in patients with brain metastases, as well as on the increasing relevance of neuroradiology in this therapeutic setting.