p27 KIP1 is a member of the Cyclin Inhibitory Protein/Kinase Inhibitory Protein （CIP/KIP） family of cyclin-dependent kinase （Cdk） inhibitors. It plays roles in all phases of the cell division cycle. Its inhibitory binding to CDK2/cyclin E and other CDK/cyclin complexes enforces the G1 restriction point. Thus, important cellular functions as the cell division cycle, respiration, RNA processing, translation, and cell adhesion, are under p27 KIP1 regulation. Loss or reduced expression is associated with poor outcome in carcinoma of breast, prostate, GI tract and lung.