ERBB3 and breast carcinoma: Given upregulation of HER3 has been found to be a major mechanism underlying drug resistance to EGFR and HER2 tyrosine kinase inhibitors (for example lapatinib, gefitinib, erlotinib) [12-14], we next assessed the effect of perhexiline combined with lapatinib, an agent commonly used to treat HER2-positive breast cancer.