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

BACKGROUND, Anti-alpha-inhibin, an antibody directed against a peptide horm one, has been shown to be a useful diagnostic aid in surgical pathology mat erial for the identification of sex cord-stromal neoplasms and recently has been described in adrenocortical carcinoma (ACC). The diagnosis of ACC ver sus renal cell carcinoma (RCC) may be difficult morphologically, particular ly in fine-needle aspiration (FNA) material. To date, the immunohistochemic al distinction of ACC from RCC is based on a panel of antibodies that inclu de vimentin, cytokeratins, and epithelial membrane antigen. However, the re liability of this panel is weakened by inconsistent staining patterns. METHODS. Archival formalin fixed, paraffin embedded cell block sections fro m 45 FNAs of known primary and metastatic ACC and RCC as well as benign adr enocortical nodules were stained with anti-alpha-inhibin using an avidin-bi otin procedure. All samples were microwave pretreated and a biotin block wa s performed to reduce the background stain due to the high endogenous bioti n often present in these types of samples. RESULTS. All cases of ACC (n = 7; 100%) and benign adrenocortical cells (n = 15; 100%) were immunoreactive with the alpha-inhibin antibody, showing a diffuse cytoplasmic and granular staining pattern. The staining intensity a nd number of immunoreactive cells varied within each sample, with the cases of ACC having the greatest proportion of immunoreactive cells and the stro ngest intensity. None of the cases of RCC (n = 23; 0%) were immunoreactive with anti-alpha-inhibin, CONCLUSIONS. 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 inten se and specific immunostaining pattern for cells of adrenal origin, even in paucicellular samples, suggests potential for the widespread clinical util ity of this marker by cytopathologists. (C) 1999 American Cancer Society.