CDKN1A and neoplasm: The most important role of p53 as a transcription factor is considered to directly regulate the expression of ~ 500 target genes [29–31], such as CDKN1A (encoding cyclin-dependent kinase inhibitor 1, also known as p21 protein) [32], BBC3 (encoding Bcl-2-binding component 3) [33], BAX (encoding BCL2 associated X, apoptosis regulator) [34], FAS [35] and some other target genes so as to suppress tumor development.