CDK4 and neoplasm: Interestingly, we found that for all the patients with a CDKN2A deletion/mutation or CDK4 amplification, there was absence of RB1 deletion or mutation, and for all the patients whose tumor harbored a RB1 deletion or mutation, there was absence of CDKN2A deletion/mutation or CDK4 amplification, indicating that these two types of genomic alterations are mutually exclusive.