Anti-alpha-inhibin: marker of choice for the consistent distinction between adrenocortical carcinoma and renal cell carcinoma in fine-needle aspiration.

Anti-alpha-inhibin, an antibody directed against a peptide hormone, has been shown to be a useful diagnostic aid in surgical pathology material for the identification of sex cord-stromal neoplasms and recently has been described in adrenocortical carcinoma (ACC). The diagnosis of ACC versus renal cell carcinoma (RCC) may be difficult morphologically, particularly in fine-needle aspiration (FNA) material. To date, the immunohistochemical distinction of ACC from RCC is based on a panel of antibodies that include vimentin, cytokeratins, and epithelial membrane antigen. However, the reliability of this panel is weakened by inconsistent staining patterns. Archival formalin fixed, paraffin embedded cell block sections from 45 FNAs of known primary and metastatic ACC and RCC as well as benign adrenocortical nodules were stained with anti-alpha-inhibin using an avidin-biotin procedure. All samples were microwave pretreated and a biotin block was performed to reduce the background stain due to the high endogenous biotin often present in these types of samples. All cases of ACC (n = 7; 100%) and benign adrenocortical cells (n = 15; 100%) were immunoreactive with the a-inhibin antibody, showing a diffuse cytoplasmic and granular staining pattern. The staining intensity and number of immunoreactive cells varied within each sample, with the cases of ACC having the greatest proportion of immunoreactive cells and the strongest intensity. None of the cases of RCC (n = 23; 0%) were immunoreactive with anti-alpha-inhibin. The morphologic distinction of ACC versus RCC in FNA material from renal, adrenal, and metastatic neoplasms is not always feasible based on cytology alone. However, due to the advent of the alpha-inhibin antibody, the reliable distinction of these entities now may be possible. The intense and specific immunostaining pattern for cells of adrenal origin, even in paucicellular samples, suggests potential for the widespread clinical utility of this marker by cytopathologists.