Decision-making challenges for implantable cardioverter-defibrillator therapy in breast cancer with ventricular tachycardia and undiagnosed leptomeningeal carcinomatosis.

Anthracycline-based chemotherapy is widely used in breast cancer but carries a risk of cardiotoxicity. Leptomeningeal carcinomatosis (LC) is a rare but fatal complication of metastatic breast cancer, often presenting with diverse neurological symptoms and requiring high clinical suspicion for diagnosis. We report a woman in her early 50s with HER2-positive breast cancer who received anthracycline-based chemotherapy. After treatment, she developed refractory ventricular tachycardia and underwent implantable cardioverter-defibrillator (ICD) implantation despite preserved cardiac function. Soon after, neurological symptoms appeared, and LC was diagnosed by cerebrospinal fluid cytology without supportive imaging. Her clinical course was rapidly progressive, and she died within days of diagnosis. This case underscores challenges in cardio-oncology, particularly the appropriateness of ICD implantation in advanced cancer with limited prognosis. It highlights the importance of continuous cardiac monitoring during and after anthracycline therapy and awareness of LC, especially when neurological or autonomic symptoms emerge.