Our results show that CDK9 inhibition significantly reduces the viability of K-Ras mutant (A549, H460, H23) and EGFR mutant (H1650, H1975, PC9) lung cancer cell lines at very low nanomolar to less than 0.5 μM concentration of CDK9 inhibitors, namely, AZD4573, LY2857785, and SNS032, respectively. This evidence concerns the gene CDK9 and lung cancer.