Antibody against the p53 tumor suppressor protein recognizes a 53 kDa phosphoprotein, identified as the p53 suppressor gene product. It reacts with both the mutant and wild-type p53 forms. Positive nuclear staining with this antibody has been demonstrated as a factor in breast carcinoma, lung carcinoma, colorectal carcinoma, urothelial carcinoma and ependymoma. Anti-p53 positivity has also been used to distinguish serous uterine carcinomas from endometrioid carcinomas and as a marker for intratubular germ cell tumors.