Anaplastic malignant melanoma of the tail in non-grey horses

This is an author's peer-reviewed final manuscript, as accepted by the publisher. The published article is copyrighted by EVJ Ltd., and published by John Wiley & Sons, Inc. It can be found at: http://onlinelibrary.wiley.com/journal/10.1001/%28ISSN%292042-3292.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 summarized. Age was recorded for 9 horses and mean age was 16 years, range 8 to 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 (1 horse), chestnut (1 horse), and black (1 horse); coat colour of 1 non-grey horse was not specified. Follow up information was available for 9 horses and only 1 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 1 case with amputation site regrowth. No subjective histopathologic differences were detected in the palomino that survived as compared to horses of other coat colours. Findings suggest that anaplastic malignant melanoma of the tail in bay, chestnut, and black horses is most often a very aggressive neoplasm, but that there are rare exceptions