A case of successful pembrolizumab rechallenge in a patient with non-small-cell lung cancer and grade 3 dermatomyositis.

We report a case of dermatomyositis in a 59-year old female with advanced non-small-cell lung cancer post one cycle of first-line pembrolizumab monotherapy. Her symptoms resolved with high-dose methyl-prednisolone and subsequent prolonged oral prednisone taper over 11 weeks. She achieved durable response over 6 months without further pembrolizumab and was successfully rechallenged without recurrent high-grade immunotoxicity. To our knowledge, this is the only case of severe immune-related dermatomyositis successfully rechallenged with immunotherapy. In this case report, we highlight that dermatomyositis remains a clinical diagnosis with no reliable autoimmune antibody marker. It is a rare immune-related adverse event for which clinicians must remain highly vigilant. We also discuss the rationale and clinical factors to consider on immunotherapy rechallenge decisions.