Peer-reviewed veterinary case report
Tail-base mass from a "horse of a different color".
- Journal:
- Veterinary clinical pathology
- Year:
- 2005
- Authors:
- LeRoy, Bruce E et al.
- Affiliation:
- Department of Pathology · United States
- Species:
- horse
Plain-English summary
A 14-year-old bay Thoroughbred gelding was brought in because there was a mass at the base of his tail that had been growing for about a year. During the examination, the veterinarian also found additional masses near his eye and shoulder. Tests showed that the tail-base mass was made up of abnormal cells that were likely a type of skin cancer called amelanotic melanoma, which is a form of melanoma that doesn't produce pigment. The horse was treated with a medication called cimetidine, but unfortunately, the tumor continued to grow.
Abstract
A 14-year-old bay Thoroughbred gelding was presented for evaluation of a mass at the base of the tail. The mass had been present for 1 year, and recently had begun to increase in size. Additional masses were found around the eye and shoulder. A fine-needle aspirate of the tail-base mass revealed highly anaplastic round to polyhedral cells containing dark green to black cytoplasmic granules interpreted to be melanin. Histologically, the mass was composed of pleomorphic, poorly pigmented, round to polyhedral cells interpreted to be neoplastic melanocytes. With immunohistochemistry, the cells were positive for vimentin and S-100, but negative for pancytokeratin and Melan-A. The cytologic and histopathologic diagnoses were amelanotic melanoma. The horse was treated with cimetidine, but the tumor continued to progress. In this report, we describe the cytopathologic features of an aggressive amelanotic melanoma in a non-grey horse and emphasize the unique correlation between cytologic and histologic findings.
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Search related cases →Original publication: https://pubmed.ncbi.nlm.nih.gov/15732023/