However, co-expression of cyclin D1, p21, PCNA and p53 was previously observed in a subset of patient population [44]; Co-expression of cyclin D1, p21 and PCNA was contributed to the role of cyclin D1 for tumor proliferation, while p53 was inversely associated with cyclin D1 levels, suggesting that overexpression p53 protein is acting to inhibit cellular proliferation [45]. This evidence concerns the gene PCNA and neoplasm.