Congenital cutaneous melanoma in a dog

Background Melanocytic tumours are derived from melanocytes and are common in older dogs with dark pigmented skin. Primary congenital cutaneous melanoma has been described in domestic mammals although there are no reports in the dog. Hypothesis/objective We describe a case of canine congenital cutaneous melanoma with rapid progression to metastasis and death. Animal A male, mixed breed dog was born with a circular ulcerated lesion near the left ear. By 12 days of age the lesion had grown significantly, with multiple soft, round nodules located at the outer base of the ear. Methods and results Histopathological examination showed the proliferation of round and elongated neoplastic cells with eosinophilic cytoplasm that occasionally contained granules of melanin. Immunohistochemical analysis was positive for melan A, S‐100 protein, neuron‐specific enolase ( NSE ) and vimentin, confirming the diagnosis of melanoma. The tumour progressed rapidly and at six months the dog died suddenly. Postmortem examination revealed pulmonary, cardiac and lymph node metastases. Conclusions and clinical importance To the best of the authors' knowledge, this is the first report of a primary congenital melanoma in the dog. The neoplastic condition showed malignant behaviour and high metastatic potential.