CDKN2A H83Y lies within the ANK3 domain of the CDKN2A protein. H83Y confers a loss of function to the CDKN2A protein as demonstrated by loss of cell cycle control. The CDKN2A gene locus is altered in up to approximately 57% of glioblastoma, most commonly as a homozygous deletion, and frequently with concurrent deletion of the CDKN2B locus. CDKN2A/CDKN2B loss may be associated with increased sensitivity to CDK4/6 inhibitors. The efficacy and toxicity profiles of these inhibitors in the context of a variety of cancer types are currently under evaluation in clinical trials. CDKN2A mutations account for only 1-3% of glioblastomas and the clinical significance remains to be elucidated.