For each of the following cell cycle kinases: CDK6, CDK1, WEE-1 and cyclin C/CDK8/CDK19 we will present (1) an overview of the current knowledge of their biological functions gained from knockout mouse models, (2) the role of each protein in human cancer with emphasis on hematologic malignancies, and (3) the pharmacological inhibitors currently in clinical development to target these kinases in hematologic malignancies. Here, CDK6 is linked to cancer.