Intracranial response after extracranial radiation in a patient with rapidly progressing metastatic melanoma

Growing literature supports the synergistic effect of radiation as a primer for renewed enhanced systemic immunological responses in patients receiving immunotherapy for metastatic melanoma. Radiographic regression of extracranial tumours after treatment of intracranial metastatic lesions has been reported and these observations point to an abscopal effect that traverses the blood-brain barrier. We describe a patient with rapidly progressing metastatic melanoma despite combined immune checkpoint blockade, who achieved a complete metabolic response of both his extracranial and intracranial disease after the commencement of palliative radiation to his axilla. This is the first published case, to our knowledge, of a sustained, complete intracranial abscopal response from extracranial radiation. We discuss potential mechanistic relations between radiation, the blood-brain barrier and the abscopal effect.