CDK4 and ependymoma: Nonetheless, the role of protein kinase signaling has been implied in ependymoma tumorigenesis [41], prompting several ongoing studies evaluating TKIs targeting RET, ALK, ROS, IGFR, PDGFR, FGFR, or EGFR, as well as inhibitors targeting PI3K, mTOR, KIT, and CDK4 [25].