Severe Myocarditis after Nivolumab and Ipilimumab in a Patient with Microsatellite Instability-High Gastric Adenocarcinoma: A Case Report

Myocarditis attributable to immune checkpoint inhibitors is regarded as among the most serious complications of immunotherapeutic treatment. We report a case of gastric cancer who developed myocarditis, and subsequent late complications following treatment with nivolumab and ipilimumab. The patient was managed with corticosteroids, mycophenolate mofetil (MMF), and intravenous immunoglobulin G (IVIG), but later developed supraventricular tachycardia and deep vein thrombosis. This report emphasizes the need to enhance recognition of immune-related toxicities within non-oncology specialties to support prompt interdisciplinary collaboration and appropriate patient management. Additionally, patients can develop myocarditis-related complications even when clinically stable or near the end of treatment, underscoring the need for close and ongoing monitoring.