Rhabdomyolysis following single administration of pembrolizumab: Is severe immune-reaction a marker for durable treatment response?

•Immune checkpoint inhibitors are approved for all mismatch repair deficient tumors.•Although rare, autoimmune myositis complicating pembrolizumab therapy may be fatal.•In this case, pembrolizumab caused rhabdomyolysis but also a durable response.•Severe autoimmune reaction may be associated with durable treatment response.