p53, also known as tumor protein 53 or TP53, is a tumor suppressor and transcription factor that functions in a number of anti-cancer activities including DNA repair, cell-cycle arrest, and apoptosis in response to DNA damage or other stressors. Mutations in p53 are linked to a number of malignant tumors, including those of the breast, ovarian, bladder, colon, lung, and melanoma. p53 is overexpressed in over 50% of human cancers. Anti-p53 staining has been used to detect intratubular germ cell neoplasia, and also to distinguish between uterine serous carcinoma and endometrioid carcinoma. Positive staining of p53 detected by immunohistochemistry has been observed in colon cancer, breast cancer, lung cancer, prostate cancer and ovarian cancer.