Along with humanized monoclonal antibodies such as trastuzumab, pertuzumab, and the antibody-drug conjugate Ado-trastuzumab-DM1 (herceptin), lapatinib is the only small molecule oral tyrosine kinase inhibitor approved for treatment of HER2+ BC (Gradishar, 2013; Nielsen et al., 2013; Singh et al., 2014). This evidence concerns the gene ERBB2 and breast cancer.