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. Here, EGFR is linked to lung cancer.