Lapatinib is a small molecule tyrosine kinase inhibitor (TKI) that targets EGFR and HER2 and it is approved for use in combination with capecitabine as second-line therapy for metastatic HER2+ breast cancer that is refractory to trastuzumab, or to treat advanced hormone receptor positive HER2+ breast cancer in combination with letrozole [14, 15]. This evidence concerns the gene ERBB2 and breast cancer.