CONGRESS ABSTRACT

A 58-year-old woman with no prior cardiac history was diagnosed with HER2-negative metastatic gastric adenocarcinoma. She commenced chemoimmunotherapy with FOLFOX combined with nivolumab, an immune checkpoint inhibitor (ICI) targeting PD-1. After the second dose of nivolumab, she developed profound asthenia and myalgia. Laboratory investigations revealed marked elevations in creatine kinase (CK, 5500 U/L), and despite the absence of overt cardiac symptoms, high-sensitivity troponin I (hsTnI) testing showed a significant increase (333 ng/L). Electrocardiography demonstrated no new changes compared to prior recordings, while transthoracic echocardiography showed preserved left ventricular function with mild pericardial effusion. Given the high clinical suspicion of ICI-related myocarditis, the patient was admitted to the Cardiology Unit. Immunosuppressive therapy with high-dose methylprednisolone (1000 mg/day for three days) was promptly initiated, resulting in a favorable initial response. This was followed by a transition to oral prednisone (1 mg/kg/day) with gradual tapering. The patient's CK and hsTnI levels substantially normalized, and she was discharged with outpatient follow-up. Although the patient initially declined cardiac magnetic resonance imaging (C-MRI), subsequent follow-up revealed a relapse of CK and hsTnI elevations. Steroid therapy was increased; however, no significant improvement in laboratory markers was observed, suggesting steroid-refractory myocarditis. The patient was readmitted to the Oncology Department, and second-line immunosuppressive therapy with mycophenolate mofetil (1000 mg bid) and intravenous immunoglobulin (IVIG, 400 mg/kg/day for five days) was initiated. After four days of second-line treatment, C-MRI was performed and confirmed active myocarditis. Laboratory markers subsequently improved, and the patient was discharged with ongoing outpatient care. She remained asymptomatic with sustained reductions in CK and hsTnI levels, allowing further tapering of steroid therapy. This case highlights a severe complication of ICI therapy. Early recognition and prompt initiation of immunosuppressive treatment are critical to managing ICI-related myocarditis effectively. Given the prognostic significance of immunotherapy in oncology, further research is warranted to evaluate the feasibility of therapy rechallenge, particularly in patients with mild or low-grade myocarditis.