Atezolizumab-associated Dermatomyositis in Advanced Small-cell Lung Carcinoma

Dermatomyositis is a rare immune-related adverse event caused by immune checkpoint inhibitors. We herein report a 75-year-old Japanese man with small-cell lung carcinoma who developed dermatomyositis after the administration of atezolizumab. He developed rashes on day 13 and myalgia and motor weakness on day 30 of the first administration of atezolizumab. Anti-transcriptional intermediary factor 1-gamma antibody was positive, and serum interleukin-6 levels were prominently elevated in the acute phase. Symptoms were improved by corticosteroid therapy. This is the first report of dermatomyositis associated with atezolizumab. Clinicians should be aware of the possibility of dermatomyositis after the administration of immune checkpoint inhibitors.