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

Abstract 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‰ ± 1.2‰ (SD) in normal adrenal glands, 11.3‰ ± 16.0‰ in adenomas, and 185.8‰ ± 60.3‰ in carcinomas ( P 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.