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

Objectives. To evaluate the utility of Ki-67 immunohistochemical analysis i n the differential diagnosis between benign and malignant adrenocortical ne oplasms. Methods. Tissue specimens were obtained from 37 patients referred to our in stitute from 1990 to 1999. The indications for adrenalectomy were adrenal-d ependent Gushing syndrome (n = 9), hyperandrogenism (n = 1), mineralocortic oid excess (n = 8), and nonfunctioning adrenal masses (n = 19). The histolo gic diagnosis was cortical adenoma in 26 of 37 patients and cortical carcin oma in the remainder. Normal adrenal glands were obtained from subjects who underwent radical nephrectomy because of initial renal carcinoma. Immunohi stochemical analysis was performed using the monoclonal antibody anti-Ki-67 (clone MIB-1). The Ki-67 labeling index was expressed as the number of pos itive cells per 1000 cells. Results. The average Ki-67 expression was 2.0 parts per thousand +/- 1.2 pa rts per thousand (SD) in normal adrenal glands, 11.3 parts per thousand +/- 16.0 parts per thousand in adenomas, and 185.8 parts per thousand +/- 60.3 parts per thousand in carcinomas (P <0.0001). A threshold value of the Ki- 67 labeling index between 70<parts per thousand> and 90 parts per thousand reliably separated adenoma from carcinoma. A significant inverse correlatio n 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 ca n be useful in the differential diagnosis between adrenocortical adenoma an d carcinoma. High levels of Ki-67 seem to indicate patients with adrenocort ical cancer with a worse prognosis. UROLOGY 57: 176-182, 2001. (C) 2001, El sevier Science Inc.