A Case of Lung Cancer with Very-Late-Onset Immune Checkpoint Inhibitor-Related Myocarditis.

Immune checkpoint inhibitor (ICI)-related myocarditis has been reported to appear in the early phase after ICI initiation. Herein, we report the case of a 78-year-old man with non-small cell lung cancer. Pembrolizumab was introduced as first-line therapy. After 9 months, second-line therapy, including bevacizumab, was initiated. After another 7 months, echocardiography showed diffuse left ventricular dysfunction. Based on the histopathologic examination of the myocardium, the patient was diagnosed with ICI-related myocarditis. Initiation of prednisolone therapy improved cardiac function. This case of late-onset ICI-related myocarditis illustrates that endomyocardial biopsy can be useful in the differential diagnosis of cancer-related left ventricular dysfunction.