We first analyzed Id4 expression of SKBr3 and MCF7 breast cancer cells, carrying mutant p53R175H and wt-p53, respectively, and of SW480 (colon) and HT29 (colorectal) adenocarcinoma cells, carrying mutant p53R273H/P309S and p53R273H, respectively. This evidence concerns the gene TP53 and breast cancer.