Trastuzumab Deruxtecan (T-DXd) for People With Brain Cancer

This trial is testing a targeted cancer drug called trastuzumab deruxtecan (T-DXd) for brain cancer patients. This drug works by targeting a protein called HER2 on cancer cells and delivering a powerful chemotherapy agent directly to them. **You may be eligible if...** - You are an adult (18 or older) with one or more brain tumors scheduled for neurosurgery - You have been diagnosed with glioblastoma (an aggressive brain cancer), OR - You have a metastatic cancer that has spread to the brain and shows a history of HER2 expression or a HER2 gene mutation **You may NOT be eligible if...** - Your tumor does not have any HER2 expression or HER2 mutations - You have other medical conditions that would make this treatment unsafe Talk to your doctor to see if this trial is right for you.