A Case of HER2-low Breast Cancer Leptomeningeal Carcinomatosis Treated Successfully with Trastuzumab Deruxtecan

Abstract

A 76-year-old woman was hospitalized with chief complaints of weakness and loss of appetite 6 months after undergoing surgery for hormone receptor-positive, HER2-low (SCORE1) left breast cancer. Contrast-enhanced brain MRI led to the diagnosis of leptomeningeal carcinomatosis. After two courses of trastuzumab deruxtecan (T-DXd), the leptomeningeal carcinomatosis resolved on imaging, and the symptoms improved. In recent years, evidence has emerged for the role of T-DXd in active central nervous system metastasis, including HER2-positive leptomeningeal carcinomatosis, has emerged. However, such evidence for HER2-low breast cancer remains scarce. In addition to a literature review, we report our experience with a case of HER2-low breast cancer leptomeningeal carcinomatosis, which is known to have a poor prognosis and was treated successfully with trastuzumab deruxtecan alone, i.e., without radiotherapy.