CDKN1A and gastrointestinal stromal tumor: In this study, we examined the TP53 mutation frequency as well as the expression of clinically relevant cell cycle regulators and apoptosis modulators that are associated with impaired p53 function in 320 high risk GIST prior to adjuvant imatinib treatment cyclin D1 (CCND1), CDK4, p21 (CDKN1A), p16 (CDKN2A), E2F1, MDM2, p-RB1 and p53.