Differentiating Benign from Malignant Adrenocortical Tumors by a Single Morphological Parameter—a Clinicopathological Study on 837 Adrenocortical Neoplasias

The morphological differentiation between benign and malignant adrenocortical tumors is an ongoing problem in diagnostic pathology. In recent decades the complex scoring systems have been widely used to calculate the probability of malignancy in adrenocortical tumors on the basis of a variety of histomorphological parameters. We herewith present a substantially simplified method to diagnose adrenocortical carcinoma by a single histomorphological parameter on a consecutive series of more than 800 adrenocortical tumors. Between January 2000 and May 2019, altogether 2305 adrenalectomies for of all types of diseases were removed, approximately 98% by minimally invasive approaches. After exclusion of pheochromocytomas, adrenal ganglioneuromas, adrenal metastases, Cushing’s disease related specimens, and Conn’s adenomas, the present series finally consisted of 837 adrenocortical tumors. All tumors were analyzed by experienced pathologists of a single institution using standard histopathological methods (Hematoxylin-Eosin and Ki67 stained sections). Clinical and histopathologic data were prospectively collected and retrospectively analyzed. Clinically, 385 patients had 420 functioning tumors (FT), and 417 had non-functioning adrenal tumors (NFT). The mean size of FT was 3.8 ± 1.4 cm (range 0.5–16 cm) and for NFT 4.5 ± 1.6 cm (range 1.5–18 cm). Histomorphologically, 32 adrenal tumors were classified as adrenocortical carcinoma (ACC; 3.8%). In all 32 cases (tumor size 9.1 ± 4.0 cm, range 3–18 cm), confluenting tumor necrosis could be demonstrated. The remaining 805 tumors (control group) completely lacked this highly reproducible single morphological feature. Ki67 levels above 10% were found in 31 of 32 ACCs and never in adrenocortical adenomas (ACA). With a mean follow-up of 8.2 years, 24 out of 32 patients primarily diagnosed as ACC developed distant metastases (75.0%), whereas all patients in the control group remained free of local or distant recurrence. We conclude that a single morphological parameter (confluenting tumor necrosis) is sufficient to predict a poor clinical course in adrenocortical tumors. The histomorphological diagnosis of this parameter is straightforward and highly reproducible.