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Miguel N Burnier, Silvin Bakalian, Erin Mayo Goldberg, Eduardo Perlmann, Paulo S M Barros, Nancy E. Mayo; A novel classification of canine uveal melanoma: the importance of melanocytoid-type of uveal melanoma in dogs. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):5307.
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© ARVO (1962-2015); The Authors (2016-present)
Canine uveal melanoma is a pigmented uveal tumor that rarely metastasizes. They are erroneously referred in the literature as melanocytomas, which is a benign melanocytic tumor. In contrast to human melanoma, the histopathological features of canine uveal melanomas exhibit classical and melanocytoma-type cells that display malignant features. The aim of this study is to describe these intraocular melanocytic lesions in dogs, propose a new classification, and compare these features with human uveal melanoma.
Sixty-seven enucleated canine eyes with the clinical presentation of an intraocular pigmented tumor were evaluated. Three cases were excluded from the study (one squamous cell carcinoma and two melanocytomas). In total, 64 malignant melanomas were classified into two groups (melanocytoid or classic) according to the presence or absence of large melanocytes with abundant cytoplasm and medium sized nuclei (M cells), respectively. Histopathological characteristics were compared between the two groups using Chi-square and t-tests. Multivariate discriminant analysis was conducted to identify features that discriminated the two groups.
Among the 64 tumors, 28 were classic and 36 were melanocytoid type. Classic melanomas were larger than melanocytoid type (18.0 mm vs. 13.6 mm; P=0.0033). Four variables (tumor size, presence of histiocytes, degree of pigmentation, and mitotic activity) were identified as discriminating between these two types, with an accuracy of 68% for classic and 100% for melanocytoid. Melanocytoid-type tumors had a smaller average size, abundant histiocytes, high degree of pigmentation, and the majority low mitotic activity (0-1 mitoses).
To the best of our knowledge, this is the largest series of canine uveal melanomas.<br /> Canine uveal melanoma should be further classified into classic and melanoytoid-type. The melanocytoid-type melanomas possess fewer malignant features and are characterized by the presence of M cells. This classification suggests that melanocytoid-type tumors have a better prognosis than the classic type. This study reclassifies previous tumors that were called “melanocytomas” as malignant “melanocytoid-type” tumors. Thus, the term melanocytoma used ubiquitously is a misnomer in dogs as it is suggestive of a benign lesion when these lesions have an infiltrative pattern.
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