Based on these previous results, we hypothesized that EGFR expression levels could affect the treatment of HER2+ breast cancer patients through dimerization with HER2+, further leading to differences in reactivity to anti-HER2 antibodies such as trastuzumab (TRZ) and trastuzumab emtansine (T-DM1). The gene discussed is EGFR; the disease is breast cancer.