Autoimmune pancerebellitis associated with pembrolizumab therapy

Checkpoint proteins reduce immune-mediated responses to promote self-tolerance and prevent autoimmunity. Programmed cell death protein 1 (PD-1) is a checkpoint receptor protein expressed on leukocytes that inactivates T cell-mediated immunity when bound to ligand PDL1. Certain tumors can escape immune-mediated destruction by expressing high concentrations of PD-L1, evading host surveillance.1 PD-1 pathway inhibitors effectively treat multiple malignancies including melanoma, non-small cell lung cancer, and squamous cell carcinoma.2 However, there is increasing recognition of immune-related adverse events (irAE) associated with checkpoint inhibitor therapy due to dysregulated immune system activation.1 We report immune-mediated cerebellitis following pembrolizumab.