ERBB2 and breast cancer: There is only one U.S. Food and Drug Administration (FDA)-approvedsystemic therapy indicated for breast cancer BM:46 tucatinib with trastuzumab and capecitabine for patientswith metastatic HER2+ breast cancer.47,48 This is partlydue to the challenges associated with the dosing and scheduling ofcytotoxic drugs, as they often result in adverse toxicity.