Non-ocular melanomas in cats: a retrospective study of 30 cases

Objectives The aim of the study was to describe the clinical outcome of 30 cats with non-ocular melanomas and to evaluate the association between clinical or pathological parameters and overall survival time. Methods The database of the animal histopathological laboratory of the National Veterinary School of Nantes (Oniris, Nantes, France) was retrospectively searched to identify cases of feline non-ocular melanomas between December 2009 and April 2014. For each case, clinical data, including signalment, location of the primary tumour, staging, treatment and outcome, were collected from the medical records or via interviews with referring veterinarians. Histological and immunohistochemical evaluation included mitotic index, cytonuclear atypias, junctional activity, Melan A and S100 immunostaining, and surgical margins. Univariate analysis to test the prognostic value of the different variables was performed by the Kaplan-Meier product limit method using the log-rank test of significance. Results Thirty cats were included in the study. Eleven had a cutaneous non-auricular melanoma, six had a tumour located on the pinna and 13 had a tumour in the oral cavity. Cats with auricular melanomas were significantly younger than cats with tumours in other locations. Location and presence of clinical signs were not of prognostic significance, but the achromic phenotype was significantly associated with a poorer prognosis. Twenty cats were treated with surgery and survived significantly longer than cats that received only medical treatment or that did not receive any treatment. According to our data, mitotic index, cytonuclear atypias, junctional activity, Melan A or S100 expression, and surgical margins were not associated with survival. Conclusions and relevance We show for the first time, in a large series, that the auricular form of melanoma affected significantly younger cats than other extraocular forms. Most feline non-ocular melanomas are malignant and achromic tumours are associated with a poorer prognosis. According to this study, surgery should be considered as a priority.