CDK4 and neoplasm: Tumour intrinsic mechanisms involve alterations in IFNγ, Wnt, MAPK and CDK4/6 signalling, upregulation of immune suppressive molecules and deficiency in antigen presentation while tumour extrinsic mechanisms include immune-poor or immunosuppressive tumour microenvironments devoid of activated effector immune cells due to deficiency in T cell trafficking and infiltration, or T cell exhaustion (reviewed in18,19).