Definition of p53

p53: A tumor suppressor. The designation "p53" stands for "protein 53 kilodaltons" in size.

p53 is a specific protein produced by a gene that functions to suppress the growth of tumors. The p53 gene is the most commonly mutated gene known in human cancer. Like other tumor-suppressor genes, p53 normally controls cell growth. If p53 is physically lost or is not functioning (because it has been inactivated), this may permit the cell to divide without restraint.

The level of p53 has prognostic (predictive) value. For example, breast cancer patients after mastectomy who have high levels of p53 are at higher risk for cancer recurrence than women with low levels of p53. The buildup of p53 within a cancer cell is a sign that p53 is not working properly to suppress the growth of the tumor.