RB1 and glioblastoma: The cyclin-dependent kinase 4 and 6 (CDK4/6)-retinoblastoma (RB1) signaling pathway is critical to GBM development, presenting itself as a chemotherapeutic target.1 The cyclin D-CDK4/6-RB1 axis tightly controls cell cycle progression from the pre-synthetic (G1) to DNA synthesis (S) cell cycle phase junctions.2 At the nexus of the CDK4/6-RB1 axis is RB1, responsible for regulating cell cycle progression through its inhibitory effect on the E2 transcription growth factor (E2F).