The CKIs, p16, p15, p18 and p19, inhibit the activity of the CDKs CDK4 and CDK6, thereby preventing phopsphorylation of Rb, and G1 to S phase transition (Cicenas et al., 2014), and a mouse with a Cdk4 point mutation (Arg24Cys) that resulted in insensitivity to the CKIs (Sotillo et al., 2001), developed tumours of the pituitary, pancreas and testes (Sotillo et al., 2001). The gene discussed is CDKN2A; the disease is pituitary tumor.