Immunohistochemical assessment of Ki-67 in the differential diagnosis of adrenocortical tumors.

OBJECTIVES: To evaluate the utility of Ki-67 immunohistochemical analysis in the differential diagnosis between benign and malignant adrenocortical neoplasms. METHODS: Tissue specimens were obtained from 37 patients referred to our institute from 1990 to 1999. The indications for adrenalectomy were adrenal-dependent Cushing syndrome (n = 9), hyperandrogenism (n = 1), mineralocorticoid excess (n = 8), and nonfunctioning adrenal masses (n = 19). The histologic diagnosis was cortical adenoma in 26 of 37 patients and cortical carcinoma in the remainder. Normal adrenal glands were obtained from subjects who underwent radical nephrectomy because of initial renal carcinoma. Immunohistochemical analysis was performed using the monoclonal antibody anti-Ki-67 (clone MIB-1). The Ki-67 labeling index was expressed as the number of positive cells per 1000 cells.Results. The average Ki-67 expression was 2.0 per thousand +/- 1.2 per thousand (SD) in normal adrenal glands, 11.3 per thousand +/- 16.0 per thousand in adenomas, and 185.8 per thousand +/- 60.3 per thousand in carcinomas (P <0.0001). A threshold value of the Ki-67 labeling index between 70 per thousand and 90 per thousand reliably separated adenoma from carcinoma. A significant inverse correlation was found between Ki-67 expression and overall survival in patients with adrenal carcinoma (r = -0.74, P = 0.009). CONCLUSIONS: Immunohistochemical assessment of the nuclear antigen Ki-67 can be useful in the differential diagnosis between adrenocortical adenoma and carcinoma. High levels of Ki-67 seem to indicate patients with adrenocortical cancer with a worse prognosis.