CDKN2A and neoplasm: The CDK4/cyclin-D1 axis controls the transition through the G1-phase of the cell cycle and is frequently altered in LUSC by multiple mechanisms such as CDKN2A inactivation (which encodes the p16INK4a tumour suppressor and inhibits the activity of the CDK4/cyclin-D1 complexes and E2F transcriptional activity), and cyclin-D1 amplification.