Alpha-methylacyl-CoA racemase (AMACR/P504S) can distinguish hepatocellular carcinoma and dysplastic hepatocytes from benign nondysplastic hepatocytes.

Immunohistochemical staining with alpha-methylacyl-CoA racemase AMACR (P504S) has been described in a number of normal tissues and was found to be useful for detecting malignancies including hepatocellular carcinoma (HCC). Our aim was to determine whether AMACR is differentially expressed in benign nondysplastic liver tissue, hepatocellular dysplasia, and HCC. The study material consisted of paraffin blocks containing primary HCC and surrounding liver tissue from 20 patients who underwent hepatectomy at the time of liver transplantation. Immunohistochemical stains were performed with anti-AMACR by standard methods. Staining features were characterized on the basis of the pattern and distribution of reactivity. A positive AMACR immunostain was defined as either finely stippled or coarsely granular in pattern, in a diffuse or parabasal cytoplasmic distribution. A negative AMACR immunostain was defined as absence of reactivity. Anti-AMACR immunostains were positive in malignant, dysplastic, and benign nondyplastic hepatocytes in all cases. The staining pattern was the same in malignant and dysplastic hepatocytes. It consisted of coarsely granular reactivity in a parabasal or diffuse cytoplasmic distribution. In contrast, benign nondysplastic hepatocytes were distinguished by weak, finely stippled diffuse cytoplasmic staining. Malignant and dysplastic hepatocytes showed an identical pattern of immunostaining for AMACR that was distinct from benign hepatocytes. Prospective studies are needed to determine whether staining for AMACR can distinguish HCC or dysplasia in cytologic and small histologic specimens.