ZEB1 and neoplasm: In the gefitinib‐treated group, tumor growth was suppressed with gefitinib treatment to a lesser extent in mice bearing PC9‐ZEB1 tumors than those bearing PC9‐mock (Figure 6(a)), suggesting that the antitumor effect of both concentrations of gefitinib was significantly reduced in PC9‐ZEB1 mice than that in PC9‐mock mice (Figure 6(b)).