HER2 antagonists are used to treat many HER2-positive cancers, such as HER2-positive breast cancer, gastric cancer, and non-small cell lung cancer. These medications work by targeting the human epidermal growth factor receptor 2 (HER2) on cancer cells, which helps to slow or stop the growth of these cells. HER2 antagonists are usually given as injections or infusions. Examples include Herceptin (trastuzumab), Perjeta (pertuzumab), and Enhertu (fam-trastuzumab deruxtecan-nxki).