CDKN1A and cancer: Given its differential expression and localization in human cancer, p21 could be targeted by three approaches [16]: first, increasing p21 expression, with histone deacetylase inhibitors [204] or through restoring p53 activity [205,206] as well as interfering with p21’s degradation using proteasome inhibitors [207], promotes its function as tumor suppressor and inhibits tumor growth.