Adrenal 4 binding protein (Ad4BP) is a transcription factor that regulates the expression of the steroidogenic enzymes and is expressed primarily in steroidogenic cells. We immunolocalized Ad4BP in adrenocortical carcinoma (eight cases) and various malignancies that histologically simulate an adrenocortical carcinoma to evaluate the value of Ad4BP as an immunohistochemical marker of adrenocortical carcinoma. These malignancies examined were renal cell carcinoma (20 cases), hepatocellular carcinoma (10 cases), malignant melanoma (eight cases), ovarian (six cases) and uterine (three cases) clear cell carcinoma, large cell carcinoma of the lung (five cases), and pheochromocytoma (three cases). Nuclear Ad4BP immunoreactivity was observed only in adrenocortical carcinoma cases but not in other tumors examined. Almost all of the adrenocortical carcinoma cells were immunohistochemically positive for Ad4BP including cells associated with bizarre nuclei. These results show that application of Ad4BP immunostain can contribute greatly to the differential diagnosis of adrenocortical carcinoma.
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