Adrenal cortical adenocarcinoma in a horse

Abstract Bilateral adrenocortical carcinoma was found in a 17‐year‐old mare showing weight loss and motor deficits. Grossly, the left adrenal gland was completely replaced with a tumour, and the right adrenal gland had multicentric masses in the cortex. Tumour varied from those showing structures resembling the fascicular layers of the adrenal cortex to those forming glandular structures. Tumour cells were round, oval, pleomorphic and spindle‐shaped, and varied in the amount of cytoplasm. Mitotic figures were seen, but not many. Tumour cells infiltrated the surrounding tissue through the capsule, and distant metastases were observed in the spleen and lymph nodes. No metastases were observed in the liver and lungs.