Numerous studies have shown that up regulation of p21WAF1 causes growth arrest in various cancer models and, though p21WAF1 was initially identified to be transcriptionally up-regulated by p53 in response to DNA damage, recent studies have shown that p21WAF1 can also be induced by various transcription factors with subsequent mediation of cell cycle arrest, senescence, and apoptosis in a p53 independent manner [25,26]. This evidence concerns the gene TP53 and cancer.