showed that the protein expression of p53 increases with HSV-TK/GCV treatment and that the expression of p21 is upregulated through a p53-dependent DNA damage signaling pathway, leading to a decrease in the protein expression of PCNA, cyclin B, and CDK1 and promoting cell cycle arrest in human breast cancer cells (Zeng et al., 2014). This evidence concerns the gene TP53 and breast carcinoma.