Supplementary Material for: Potential Influence of Duchenne Muscular Dystrophy Carrier on Breast Cancer Treatment-Related Cardiomyopathy: a case report

Introduction: Carriers of Duchenne muscular dystrophy (DMD) and other inherited myopathies are at risk of cardiomyopathy, and HER2-targeted therapies for breast cancer are also associated with cardiotoxicity. The coexistence of these conditions presents a novel clinical challenge. Standard baseline cardiac evaluations prior to HER2-targeted therapy do not routinely detect inherited cardiomyopathies, and genetic risk is not currently incorporated into pre-treatment assessment.
Case Report: We report the case of a woman in her 30s with HER2-positive breast cancer with baseline borderline low global longitudinal strain (GLS) who was incidentally identified as a carrier of a DMD gene mutation after her son was diagnosed with DMD and developed an asymptomatic decline in left ventricular ejection fraction during treatment.
Conclusion: This case highlights the potential role of increased cardiac surveillance and consideration of cardioprotective medications and genetic screening in patients with baseline abnormal echocardiograms prior to receiving cardiotoxic cancer therapies.