TP53 and cancer: The cyclin kinase inhibitor p21 is induced by p53 in situations of DNA damage, and it likely plays a role in the decision pathways leading to apoptosis or DNA repair [24]; for this reason, not only has p21 been proposed as a target for chemotherapy sensitization, but also, the mechanisms by which p21 becomes activated have attracted considerable interest in the study of chemotherapy-resistant cancers.