ERBB2 and breast cancer: Recently, the U.S. Food and Drug Administration (FDA) approved tucatinib in combination with trastuzumab and capecitabine for patients with advanced HER2-positive breast cancer, including patients with BM, who have received one or more prior anti-HER2-based regimens for metastatic disease; importantly, this was the first FDA approval that specified BM in the indication statement [24,28].