ERBB2 and breast carcinoma: Moreover, unlike HER2-amplified breast cancer, tumors harboring HER2 mutations appear to be resistant to standard HER2-targeted antibodies, including trastuzumab.23HER2-mutant breast cancers exhibit mixed responses to the most commonly used small molecular inhibitor, lapatinib, although they may be more sensitive to more potent irreversible HER2 inhibitors, such as neratinib.23,30 Lapatinib and neratinib were chosen to test the response to reversible and irreversible HER2 inhibition, respectively, utilizing two drugs that are FDA approved.