To investigate the molecular mechanism of EGFR-TKI resistance in NSCLC, EGFR-TKI-resistant PC9/GR cells and the corresponding parental PC9 cells (Fig. 1A) were used for iTRAQ-based quantitative proteomics to identify differentially expressed proteins (Fig. 1B). The gene discussed is EGFR; the disease is non-small cell lung carcinoma.