Durvalumab-associated Late-onset Myocarditis Successfully Treated with Corticosteroid Therapy.

We herein report a 66-year-old man with locally advanced non-small-cell lung cancer (NSCLC) who developed durvalumab-associated myocarditis. The patient underwent durvalumab administration every two weeks following concurrent chemoradiotherapy, without any adverse events or apparent disease progression. He presented with fatigue and dyspnea on exertion seven months after the first administration. Myocarditis was suspected based on laboratory data, an electrocardiogram, echocardiography, and magnetic resonance imaging findings. The definitive diagnosis was confirmed by a myocardial biopsy. Myocarditis was alleviated by cessation of durvalumab and corticosteroid therapy. This is a noteworthy case to describe late-onset myocarditis following the administration of durvalumab for NSCLC.