While germ line deletion of p53 in this mouse model promotes tumor formation as early as 50 days, it has been shown that postnatal p53 gene deletion leads to a tumor incidence of only 3% even 600 days after Cre recombinase transduction, indicating that the timing of p53 loss is a critical determinant for tumor incidence [23, 24]. This evidence concerns the gene TP53 and neoplasm.