Cutaneous amelanotic melanoma in a young dog

Abstract

The aim of this study was to report the clinicopathological aspects of a dog with a young with amelanotic melanoma. A six-month-old male French Bulldog canine was seen with a history of a rapidly growing nodule in the humerus-radio-ulnar joint region. Macroscopically, the nodule was shaped like a non-pigmented button. Surgical excision of the mass was performed. Microscopically, non-encapsulated and infiltrative neoplastic proliferation was observed, composed of round cells, with basophilic, sometimes abundant, cytoplasm and polychromatic nuclei. Cellular pleomorphism was high and there was marked anisocytosis and anisokaryosis. For diagnostic complementation, immunohistochemical examination was performed using markers for cytotokeratins (AE1/AE3), Melan A, Vimentin, PNL-2 and S100. The diagnosis of amelanotic melanoma was based on positive immunostaining for PNL-2 and S100 in more than 80% of tumor cells. In this study, the tumor had histological features of a round cell tumor, possibly a mast cell tumor or a cutaneous histiocytoma. However, the use of the immunohistochemistry technique was crucial for the correct diagnosis of the neoplasm. In this study, attention is drawn to the occurrence of melanomas with histological characteristics of round cell tumors in young animals and the use of immunohistochemistry as an indispensable tool for the correct diagnosis of the neoplasm.