As far as targets other than HER2, HER3 overexpression seems to be associated to resistance to anti-HER2 agents (both trastuzumab and T-DM1) [41]; in fact, HER3 inhibition demonstrated to overcome the acquired trastuzumab resistance in HER2-positive gastric cancer-derived xenograft [67]. The gene discussed is ERBB2; the disease is gastric cancer.