Trastuzumab deruxtecan also known as fam-trastuzumab deruxtecan and sold under the brand name Enhertu, is a medication used for the treatment of adults with unresectable (unable to be removed with surgery) or metastatic (when cancer cells spread to other parts of the body) HER2-positive breast cancer who have received two or more prior anti-HER2-based regimens in the metastatic setting.