CDK4 and cancer: CDKN1A (p21), cyclin‐dependent kinase inhibitor 1A, is a mediator of p53 tumour suppressor activity based on growth arrest, differentiation and senescence functions52; CDK4 is a member of the Ser/Thr protein kinase family, and its partner gene CDK6, is the core driver of the cell cycle53 and plays a crucial role in the occurrence and development of various malignant tumours including GC; p21 can promote tumorigenesis by promoting the assembly of CDK4/CDK6 complex.54