Adrenocortical carcinoma. An immunohistochemical comparison with renal cell carcinoma.

The diagnosis of adrenocortical carcinoma (ACC) is often difficult, because this tumor may present with direct extension into adjacent renal parenchyma or with metastatic disease. Renal cell carcinoma and other histologically similar tumors are potentially confused with ACC by conventional light microscopy, and their separation from the latter is often impossible without the aid of additional studies. Furthermore, the distinction between adrenal cortical adenoma and ACC may also be problematic. Because of these factors, the authors studied 10 cases each of ACC, adrenocortical adenoma, and renal cell carcinoma (RCC) immunohistochemically, in an attempt to develop objective parameters which may aid in this differential diagnostic dilemma. Nontrypsinized, formalin-fixed, paraffin-embedded specimens were used in all cases, and tissue from the adrenocortical tumors was also studied for intermediate filament content after protease digestion. All 20 nontrypsinized adrenocortical neoplasms were positive for vimentin, but not for cytokeratin, epithelial membrane antigen, or blood group isoantigens. Conversely, each of 10 cases of RCC expressed epithelial membrane antigen, cytokeratin, and blood group isoantigens, but none was immunoreactive for vimentin. Two adrenocortical carcinomas and three adenomas manifested cytokeratin positivity after trypsin digestion. There were no significant differences between the immunostaining profiles of ACC and adrenocortical adenoma, which suggest that this distinction must still rely upon clinical and morphologic criteria.