CDK4 and cancer: OncoPPi identifies prominent protein interaction hubs with new PPI partners revolving around key cancer drivers such as MYC, STK11, RASSF1 and CDK4, uncovers interactions for non-enzymatic proteins, suggests cross-talk between oncogenic pathways, implicates novel mechanisms of action for major oncogene drivers such as transcription factor MYC, and reveals connectivity of tumour suppressors with actionable targets, such as the highly altered lung cancer tumour suppressor STK11 with CDK4.