Unilateral malignant melanoma of the adrenal gland with metastatic spread to the thorax in a horse

A 7-year-old grey horse that had a history of inappetence, weight loss, weakness, dyspnoea, coughing and intermittent colic was examined post-mortem. A melanoma, confirmed histologically, was found in the right adrenal gland and had eroded into the posterior vena cava. Thoracic metastases were also identified. The skin, including the legs, trunk and perineum was normal with no evidence of melanomas. This was considered to be a primary, malignant melanoma, a novel finding in the adrenal gland of the horse.