Traditional anti-HER2 drugs, including trastuzumab, pertuzumab, and lapatinib, tend to be ineffective in patients with breast cancer who exhibit low HER2 levels (Baselga et al., 2016; Burris et al., 2011; Kim et al., 2016; Krop et al., 2012; Lee et al., 2016). Here, ERBB2 is linked to breast cancer.