Currently, small molecule inhibitors or antibodies targeting HER2 have been approved for treatment of patients with HER2-positive breast cancer, non-small cell lung cancer (NSCLC), and gastroesophageal cancer (Iqbal and Iqbal, 2014; Cameron et al., 2017; Kneissl et al., 2017; Liu et al., 2018; Okamoto et al., 2020). The gene discussed is ERBB2; the disease is breast cancer.