Hou and colleagues assessed the methylation status at the promoter region of RASSF1A and GADD45β genes in acquired gefitinib-resistant lung adenocarcinoma PC9 (harboring EGFR exon19 deletion) and PC9/GR (harboring EGFR exon19 deletions and acquired EGFR exon20 p.T790M mutation) cell lines. This evidence concerns the gene EGFR and lung adenocarcinoma.