Breast cancer consists of a group of biologically and molecularly heterogeneous diseases that originate from the breast and can be divided into four major subtypes: luminal-A, luminal-B, human epidermal growth factor receptor 2 (HER2) positive, and triple-negative breast cancer (Feng et al., 2018; Wang et al., 2020a; Tsang and Tse, 2020). The gene discussed is ERBB2; the disease is breast cancer.