Although the (p53rk1/rk1) mouse of Supplementary 3 was an unsuccessful reversible p53 knockout mouse, expression of p53 protein in this line is less than 10% of that of wild-type mice in the absence of cre; and it may therefore be a valuable animal model for understanding the effect of suppressed p53 expression level in tumor development. This evidence concerns the gene TP53 and neoplasm.