ERBB2 and breast cancer: The same phenomenon occurs in 1.5–6% of breast cancers (Gibbons-Fideler et al. 2019; Ellis et al. 2005) and 2.1–4% of gastric cancers (Kim et al. 2007; Tafe et al. 2011; Hofmann et al. 2008; Robertson et al. 2018), and is attributed to HER2 intra-tumoral heterogeneity, co-amplified/polysomy CEP17 and monosomy CEP17, and so on (Gibbons-Fideler et al. 2019; Robertson et al. 2018).