CDK4 and pancreatic ductal adenocarcinoma: Inhibition of the cell cycle kinases CDK4 and CDK6 is now part of the standard treatment in advanced breast cancer; recently, a study has revealed that the sequential administration of CDK4/6 inhibitors after taxanes cooperates to prevent cell cycle re-entry in pancreatic ductal adenocarcinoma (PDAC) [79], indicating that cell-cycle-dependent kinases could be a potential target in preventing the quiescence-to-proliferation switch.