Capecitabine, Tucatinib, and Intrathecal Trastuzumab for Breast Cancer Patients With Leptomeningeal Disease

This study is testing a three-drug combination — capecitabine (oral chemotherapy), tucatinib (targeted therapy), and trastuzumab (given directly into the spinal fluid) — for HER2-positive breast cancer that has spread to the lining of the brain and spinal cord (called leptomeningeal disease). **You may be eligible if:** - You are 18 or older - You have HER2-positive metastatic breast cancer (confirmed by testing) - Cancer has spread to the lining of the brain or spinal cord, confirmed by MRI or spinal fluid testing - You are in reasonably good physical condition (ECOG 0–2) - Your life expectancy is at least 2 months - You are on a stable steroid dose (if taking steroids for brain symptoms) **You may NOT be eligible if:** - Your breast cancer is HER2-negative - You have not had leptomeningeal involvement confirmed - Your general health is too poor to tolerate treatment - You are pregnant or breastfeeding - You have had recent radiation or surgery within 2 weeks before joining the study Talk to your doctor to see if this trial is right for you.