ERBB2 and breast cancer: The newest agent in the armamentarium against HER2-positive breast cancer is ado-trastuzumab emtansine(Kadcyla), also known as T-DM1, which earned FDA approval in February 2013 for metastatic HER2-positive breastcancer that has progressed on a trastuzumab-containing regimen (Genentech, 2013).