Efficacy and Safety of Intrathecal Administration of Thiotepa in Combination With Trastuzumab in Breast Cancer With Leptomeningeal Metastasis

This study is testing thiotepa (a chemotherapy drug) injected directly into the fluid around the brain and spine (intrathecal administration) combined with trastuzumab (a targeted therapy) for patients with HER2-positive breast cancer that has spread to the leptomeninges — the thin membranes surrounding the brain and spinal cord — a serious and difficult-to-treat complication. **You may be eligible if...** - You have confirmed HER2-positive breast cancer (tested by biopsy) - Your cancer has spread to the leptomeninges, confirmed by spinal fluid analysis and brain imaging - You have an Ommaya reservoir implanted in your head (or are a candidate for one) — a device that allows drug delivery directly into brain fluid - You have adequate bone marrow, liver, and kidney function **You may NOT be eligible if...** - Your cancer is not HER2-positive - Your cancer has not spread to the leptomeninges - You cannot have an Ommaya reservoir implanted - Your overall condition (KPS below 30) is too poor for treatment Talk to your doctor to see if this trial is right for you.