Interestingly, the MDM4 inhibitor, SJ‐172550, and the MDM2 inhibitor, nutlin‐3, showed a synergistic effect with erlotinib in erlotinib‐resistant lung cancer cell lines, NCI‐H820 (Fig. 3B) and NCI‐H1975 (Fig. S4B). This evidence concerns the gene MDM4 and lung cancer.