ALOX5 and cancer: To validate whether differentially expressed proteins identified in our proteomic study are important in regulating gefitinib resistance, we chose HMGA2 and ALOX5 for subsequent validation, because HMGA2 is a known driver promoting tumor metastasis and a molecular target in many cancers,20 but it is significantly downregulated in gefitinib‐resistant PC9/GR cells (Figure 1C).