We performed in vitro proliferation, colony formation, apoptosis, and senescence assays, and Western blots, on a panel of 11 KRAS mutant CRC cell lines treated with the MEK inhibitor MEK162, the CDK4/6 inhibitor palbociclib, or the combination...Combined inhibition of both MEK and CDK4/6 is effective in preclinical models of KRAS mutant CRC and justifies a planned phase II clinical trial in patients with refractory KRAS-mutant CRC.