Anaplastic malignant melanoma of the tail in non‐grey horses

Information regarding signalment, clinical findings, treatment and outcome of 5 previously reported cases of anaplastic malignant melanoma of the tail in non‐grey horses and of 5 additional cases are summarised. Age was recorded for 9 horses and mean age was 16 years, range 8–23 years. Gender was recorded for 8 horses and 6 of these 8 horses were male horses over 14 years of age. The most common coat colour was bay (6 horses). Other coat colours were palomino (one horse), chestnut (one horse) and black (one horse); coat colour of one non‐grey horse was not specified. Follow‐up information was available for 9 horses and only one horse, a palomino, survived more than 10 months following diagnosis and tail amputation. Surgical excision, including tail amputation and medical therapy with oral cimetidine, was not effective in non‐grey, non‐palomino horses. Tumour recurred on tail tissue remaining after amputation in 2 horses, widespread metastases were documented in 4 cases and metastasis was suspected at the time of death or euthanasia in 3 cases, including one case with amputation site regrowth. No subjective histopathological differences were detected in the palomino horse that survived as compared to horses of other coat colours. Findings suggest that anaplastic malignant melanoma of the tail in non‐grey horses is most often a very aggressive neoplasm, but that there are rare exceptions.