Positive staining with anti-AFP antibody is seen in hepatocytes of fetal liver and hepatoma. Since only the traces of AFP are found in adult serum, elevated levels suggest either a benign or malignant lesion of the liver, a yolk sac carcinoma, or one of a few other tumors. In conjunction with elevated serum levels, AFP has been immunohistochemically demonstrated in yolk sac carcinomas of gonadal and extragonadal sites, in hepatic malignancies and a few other neoplasms. The antigen is not denatured by most fixatives.