Interestingly, the Human Protein Atlas [36] contains immunohistochemistry staining of the PCNA protein (antibody HPA030522) in normal breast tissue (Fig. 4b) versus the overexpression in breast cancer ductal carcinoma (Fig. 4c) implicating the abundance of the protein in breast cancer tissue as a potential biomarker [37]. This evidence concerns the gene PCNA and breast ductal adenocarcinoma.