Trastuzumab Rezetecan Combined With Radiotherapy Versus Trastuzumab Rezetecan in the Treatment of HER2-positive Advanced Breast Cancer With Brain Metastases

This study is testing whether combining a targeted antibody-drug therapy called trastuzumab rezetecan with radiation therapy works better than trastuzumab rezetecan alone for women with HER2-positive advanced breast cancer that has spread to the brain. Brain metastases from HER2-positive breast cancer are difficult to treat, and this study aims to find a more effective approach. **You may be eligible if...** - You are a woman aged 18 or older - You have confirmed HER2-positive advanced breast cancer - You have at least one measurable brain tumor that has not yet been treated - You have not received prior brain radiation and do not need immediate local treatment - Your life expectancy is at least 6 months - Your major organ function is adequate **You may NOT be eligible if...** - You have cancer spreading to the membrane around the brain (leptomeningeal metastasis) - You need urgent brain surgery for complications - You have previously been treated with trastuzumab deruxtecan or a similar antibody-drug conjugate - You have uncontrolled heart disease or significant lung disease - You have had another cancer in the past 5 years (with minor exceptions) - You are pregnant or breastfeeding Talk to your doctor to see if this trial is right for you.