In vitro experiments have suggested that constant ligand stimulation in the in vivo microenvironment may activate HER3 and promote tumor growth or mitigate the efficacy of HER2 inhibitors in HER2-amplified cancers (Claus et al., 2018; Leung et al., 2015; Sato et al., 2013; Wilson et al., 2012; Xia et al., 2013; Yang et al., 2017). The gene discussed is ERBB2; the disease is cancer.