This will be an open label Phase I/II dose escalation study evaluating the combination of the CDK4/6 inhibitor palbociclib (PD-0332991) and the MEK inhibitor PD-0325901. To determine the maximally tolerated dose (MTD) and recommended phase 2 dose (RP2D), a 3+3 dose escalation protocol will be undertaken. Once the RP2D has been determined, the study will then evaluate, in a randomized phase II study design, the combination of palbociclib and PD-0325901 compared to PD-0325901 alone and palbociclib alone in KRAS mutant NSCLC.