KADCYLA is a prescription medicine used as an adjuvant (after surgery) treatment for HER2-positive early breast cancer when the patient has taken neoadjuvant (before surgery) treatment including a taxane and trastuzumab (Herceptin®) and there is cancer remaining in the tissue removed during surgery. Patients are selected for therapy based on an FDA-approved test for KADCYLA. KADCYLA is a prescription medicine used to treat HER2-positive breast cancer that has spread to other parts of the body (metastatic breast cancer) after prior treatment with trastuzumab (Herceptin) and a taxane. Prior treatment could have been for the initial treatment of breast cancer or for the treatment of cancer that had spread to other parts of the body. Patients are selected for therapy based on an FDA-approved test for KADCYLA.