KRAS and cancer: Using the CRISPR/Cas9 system, we generated isogenic cell lines with EGFR/KRAS co-mutations from the KRAS-mutated A549 cell line (Figs 1 and 2), and demonstrated that these co-mutated cell lines were more susceptible to EGFR-TKIs, but not to conventional anti-cancer drugs, than parental cells (Fig 4).