Tumor protein p53, also known as p53, is any isoform of a protein encoded by homologous genes in various organisms, such as TP53 (humans) and Trp53 (mice). This homolog is crucial in multicellular organisms, where it prevents cancer formation, thus, functions as a tumor suppressor. As such, p53 has been described as “the guardian of the genome” because of its role in conserving stability by preventing genome mutation.

p53 has many mechanisms of anticancer function and plays a role in apoptosis, genomic stability, and inhibition of angiogenesis. In its anti-cancer role, p53 works through several mechanisms: It can activate DNA repair proteins when DNA has sustained damage. Thus, it may be an important factor in aging; It can arrest growth by holding the cell cycle at the G1/S regulation point on DNA damage recognition (if it holds the cell here for long enough, the DNA repair proteins will have time to fix the damage and the cell will be allowed to continue the cell cycle); It can initiate apoptosis (i.e., programmed cell death) if DNA damage proves to be irreparable.