Dermatomyositis, pembrolizumab, and squamous cell carcinoma of the lung.

Cancer immunotherapy has impacted the treatment of numerous tumor types, including skin, lung, and colon cancers. Immune checkpoint inhibitors (ICI) activate the immune system to attack cancer cells, but this mechanism can also impact healthy cells. Dermatomyositis, an autoimmune syndrome affecting multiple organ systems, is often associated with cancer as a paraneoplastic syndrome, but this syndrome can also be induced by ICI. Here, we describe a case of dermatomyositis in a patient receiving pembrolizumab for treatment of squamous cell carcinoma of the lung and discuss the importance of recognizing complications of ICI.