ERBB3 and lung cancer: Feedback phosphorylation of EGFR at Thr669 by ERK has been found to negatively regulate constitutive EGFR tyrosine kinase activity and HER3‐driven Akt activation by suppressing heterodimerization of EGFR/HER3 in lung cancer and triple‐negative MDA‐MB‐468 breast cancer cells (Sato et al., 2013; Turke et al., 2012).