CDK4 and glioblastoma: Co-deletion of CDKN2C, a cyclin-dependent kinase inhibitor and tumor suppressor, and CDKN2A in GBM cells predicted sensitivity to palbociclib (PD0332991), a selective CDK4/6 inhibitor that is being evaluated in an ongoing GBM clinical trial (NCT03158389) (Wiedemeyer et al., 2010; Cen et al., 2012).