Trastuzumab Deruxtecan (T-DXd) is an antibody-drug conjugate medication used to treat breast cancer. It specifically targets cancer cells that have high levels of a protein called HER2. The medication works by combining a targeted antibody (which finds and attaches to cancer cells) with a chemotherapy drug (which helps destroy the cancer cells). This medication is particularly important for treating advanced or metastatic breast cancer that has spread to other parts of the body, including cases where cancer may have spread to the brain.

HER2-positive breast cancer – A type of breast cancer that develops when breast cells have too many copies of the HER2 gene, making excess HER2 proteins that promote cancer cell growth. This form of breast cancer tends to grow and spread more aggressively than other types. The cancer begins in the breast tissue and can affect various parts of the breast. As the disease progresses, cancer cells may spread to other parts of the body, including the brain (brain metastasis). Brain metastasis occurs when cancer cells from the breast travel through the bloodstream or lymphatic system and form new tumors in the brain.

Brain metastasis – A condition that occurs when cancer cells spread from their original location to the brain, forming secondary tumors. In breast cancer patients, these metastases develop when cancer cells break away from the primary breast tumor and travel through the bloodstream or lymphatic system to the brain. The metastatic tumors can form in various parts of the brain and may be single or multiple. These secondary tumors grow in the brain tissue and can affect normal brain function.