CDK4 and sarcoma: Dysregulation of the Cyclin D–CDK4/6 axis through various mechanisms, such as the gene amplification of positive regulators, or gene rearrangement; loss of negative regulators; epigenetic alterations; and point mutations in significant Cyclin D–CDK4/6 pathway components, leads to uncontrolled cell proliferation frequently shown in many types of cancer including sarcomas [69,102].