Lapatinib is an oral dual kinase inhibitor targeting both Epidermal Growth Factor Receptor (EGFR) and Human Epidermal Growth Factor Receptor 2 (HER2) that has demonstrated clinical efficacy in patients with advanced or metastatic HER2+ breast cancer who have received prior therapy, including an anthracycline, a taxane, and trastuzumab.8 This evidence concerns the gene ERBB2 and breast cancer.