CDKN1B and cancer: Cell division depends on the activation of cyclin, which binds to CDKs to induce cell cycle progression towards S phase and later to initiate mitosis; uncontrolled CDK kinase activity is one of the major causes of cancer progression as their functions are tightly regulated by CDKIs such as the Cip1/p21 and Kip1/p27 proteins in normal cell cycle progression [38].