Tucatinib is an oral medication that works by blocking a specific protein called HER2. It belongs to a group of drugs called tyrosine kinase inhibitors. This medication specifically targets cancer cells that have mutations in the HER3 gene, helping to slow down or stop cancer growth in breast cancer patients.

Trastuzumab is an antibody treatment given by infusion that targets the HER2 protein on cancer cells. It works by attaching to HER2 receptors on cancer cells and blocking them from receiving growth signals. This helps to slow down or stop the growth of cancer cells. It has been used for many years as a standard treatment for certain types of breast cancer.

HER3-mutant and HER2-negative Metastatic Breast Cancer – A specific type of breast cancer that has spread beyond the breast to other parts of the body (metastatic). This condition is characterized by mutations in the HER3 (ERBB3) gene while not showing amplification of the HER2 gene. The cancer cells in this type have developed changes in the HER3 protein, which is involved in cell growth and survival. This form of breast cancer represents a distinct molecular subtype with specific cellular characteristics. The disease progresses as cancer cells continue to grow and spread to distant organs.