Severe acute myocarditis induced by 5-fluorouracil with successful rechallenge after multidisciplinary cardio-oncology evaluation: a case report

Abstract Background Fluoropyrimidines are among the most common chemotherapeutic agents associated with cardiotoxicity, typically presenting as angina due to coronary vasospasm. Severe manifestations such as myocarditis and cardiogenic shock are rare, and rechallenge after cardiotoxicity is generally discouraged. We report a case of acute 5-fluorouracil–induced myocarditis with successful rechallenge after multidisciplinary evaluation. Case summary A 30-year-old man with unresectable rectal adenocarcinoma developed acute cardiotoxicity during the first FOLFOX-6 cycle, presenting with abdominal pain and palpitations. ECG showed atrial fibrillation and ST-segment elevation. Echocardiography revealed severe biventricular dysfunction with elevated cardiac biomarkers. Coronary angiography excluded obstructive disease, and cardiac magnetic resonance confirmed acute myocarditis with diffuse edema and non-ischaemic late gadolinium enhancement. Guideline-directed heart failure therapy led to rapid functional recovery within days. Following multidisciplinary cardio-oncology assessment, chemotherapy rechallenge under continuous monitoring was performed without recurrence of major adverse events. Subsequent cycles were well tolerated, and follow-up CMR showed preserved ventricular function with residual non-ischaemic LGE. Discussion This case highlights the importance of early recognition of fluoropyrimidine cardiotoxicity, the role of multidisciplinary cardio-oncology management, and the potential feasibility of rechallenge in carefully selected patients.