Notably, previous reports have demonstrated that CDKN1A (p21), PCNA, cyclin D1, vimentin, E‐cadherin and MMP‐9 are key factors involved in the modulation of tumour cell proliferation/migration/invasion/EMT in a variety of human cancers, including BC.25, 26, 27, 28, 29. This evidence concerns the gene PCNA and breast cancer.