Intrathecal Trastuzumab as a Novel Simplified Therapeutic Strategy for Isolated Metastases in the Leptomeninges in HER2-Positive Breast Cancer: A Case Report and Review of Literature

Abstract Leptomeningeal metastases is one of the dreaded complications of metastatic breast cancer, which has a very poor prognosis despite standard treatment, which includes systemic chemotherapy, targeted therapy, and radiation therapy. Intrathecal (IT) therapy has also been used in various studies, which includes IT methotrexate and IT trastuzumab (if the cancer is found to be HER2 + ). We report our experience with the combined modality treatment of systemic chemotherapy with IT trastuzumab in a 52-year-old female patient diagnosed with left breast carcinoma (ER/PR/HER2 status 4/4/3) who progressed in the first year of adjuvant hormonal therapy and developed isolated leptomeningeal metastases. She initially presented with seizures, headache, and neck stiffness. Leptomeningeal enhancement was observed in the magnetic resonance imaging scan of CNS. Positron emission tomography/computed tomography scan showed no evidence of distant metastasis. After confirming cerebrospinal fluid involvement by cytology, the patient was started on IT trastuzumab along with systemic chemotherapy. This resulted in considerable clinical and neurological improvement.