As HER3 expression is a major cause of cancer treatment failure [35, 36], majority of the current studies focus on defining the molecular basis of HER3 signaling-mediated therapeutic resistance in a wide variety of cancers, including HER2-positive breast cancer [28, 31], castration-resistant prostate cancer [37], platinum-resistant/refractory ovarian cancer [38, 39], and EGFR-TKI resistant NSCLC [40–43]. The gene discussed is ERBB2; the disease is breast cancer.