Iridociliary Amelanotic Melanoma in a Cat
World Small Animal Veterinary Association World Congress Proceedings, 2009
D.C. Leandro; E. Perlmann; R. Squarzoni; A.M.V. Safatle; P.S.M. Barros
University of São Paulo, São Paulo, Brazil

Anterior uveal melanoma is the most common primary intraocular tumor in cats. Recent studies have shown that the ocular melanoma is more frequent than oral or cutaneous forms. Some experimental studies have also shown the association between feline sarcoma virus and the development of the anterior uveal melanoma in cats. The most common clinical manifestation of uveal melanoma is the gradual and diffuse hyperpigmentation of the iris, which may present as pigmented nodules. Buphthalmia as a result of secondary glaucoma and uveitis can also be seen in some cases. The diagnosis of uveal melanoma is often made clinically. Investigations such as fine needle aspirates of the iridal surface or iridal biopsies can be performed, although rarely indicated. The early surgical treatment (enucleation) is recommended in most cases, followed by the histopathological evaluation and, if necessary, immunohistochemistry. This study aims to describe a case of amelanotic uveal melanoma in a cat, since few reports are available in veterinary medicine. A domestic short-haired cat, male, 17 years old, was presented to the ophthalmology section (Department of Surgery, School of Veterinary Medicine, University of São Paulo) for evaluation of the left eye. Thickening of the iris, rubeosis iridis, hyphema, conjunctival hyperemia and buphthalmia were present. Ocular ultrasound revealed a mass localized in the iris and ciliary body. Due to the suspicion of neoplasia, enucleation was the treatment of choice. Gross examination revealed a white mass localized in the ciliary body, infiltrating the iris, and lens displacement. Microscopic examination revealed pleomorphic, large centrally and eccentric nuclei (epithelioid cell type) with anisokaryosis, pronounced nucleoli and abundant, often eosinophilic cytoplasm. Mitotic figures were frequent. Fontana Masson stain showed areas of intracellular melanin that was not demonstrated by H&E stain. Neoplastic cells were also strongly immunostained for S-100 protein. The diagnosis of an amelanotic melanoma of the anterior uvea was confirmed. Other neoplasms, such as sarcoma and lymphoma, may have a similar macroscopic appearance. Therefore, this report emphasizes the importance of the histopathological examination in confirming the diagnosis. Immunohistochemistry should be considered, since histopathological findings of the amelanotic forms differ from those observed in other types of melanoma.

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D.C. Leandro
University of São Paulo
São Paulo, Brazil

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