Fam-trastuzumab deruxtecan in a patient with metastatic human epidermal growth factor receptor 2-positive breast cancer and pre-existing cardiac failure: a case report.

BACKGROUND: Human epidermal growth factor receptor 2 (HER2)-positive breast cancer is aggressive with poor prognosis, and fam-trastuzumab deruxtecan-nxki (T-DXd), an antibody-drug conjugate (ADC), offers a promising treatment option for pretreated HER2-positive advanced or metastatic breast cancer. Patients treated with fam-trastuzumab deruxtecan may have an increased risk of developing left ventricular dysfunction. However, its safety in patients with pre-existing cardiac comorbidities remains unclear.

CASE DESCRIPTION: This report presents a 72-year-old female with type-2 diabetes and metastatic HER2-positive breast cancer, who developed cardiomyopathy [ejection fraction (EF) 35-40%, New York Heart Association (NYHA) class II-III] following liposomal doxorubicin. Due to disease progression, T-DXd was initiated. After four cycles, imaging showed favorable response without worsening cardiac function. However, by the eighth cycle, mixed response was noted along with severe gastrointestinal toxicity, including gastric perforation and diarrhea, leading to dose adjustments. Ultimately, treatment was discontinued due to disease progression and toxicity, and the patient was transitioned to palliative care. Despite concerns, cardiac monitoring showed stable EF and global longitudinal strain (GLS), suggesting potential safety of T-DXd in high-risk patients.

CONCLUSIONS: This case highlights the need for further research to assess T-DXd's safety and efficacy in patients with pre-existing cardiac dysfunction.