As HER2 mutations have been shown to reduce the efficacy of therapies commonly used to treat HER2-positive breast cancer, particularly in metastatic and previously HER2 inhibitor-treated patients (40), our data, even though limited by being an analysis only of one patient, provide novel insights into general and EGFR-TKi-specific drug efficacy in cancers bearing these aberrations. This evidence concerns the gene ERBB2 and breast cancer.