Amelanotic Melanoma in the Rabbit: A Case Report With an Overview of Immunohistochemical Characterization

An adult spayed female New Zealand white mix-breed rabbit was presented for an abnormal cutaneous pigmentation of the left nasal canthus. Biopsy samples were collected when the rabbit was under general anesthesia. Using the results of the biopsy, an initial diagnosis of carcinoma was made. The patient was referred for surgical excision followed by local radiation therapy using strontium-90. The histological appearance was most consistent with an amelanotic melanoma. Neoplastic cells strongly expressed melan-A and vimentin and failed to express pancytokeratin markers. The immunohistochemical findings supported the presumptive diagnosis of amelanotic melanoma. Owing to the high mitotic index, presence of neoplastic cells within the vessels, and incomplete surgical excision, the prognosis was poor. The owner refused further treatment and diagnostic evaluation of the patient. The rabbit was found dead in its enclosure approximately 6 months after the diagnosis. A postmortem examination was not performed. Although melanomas have been reported in rabbits, this condition appears to be underreported in pet rabbits. This case report describes the clinical presentation and diagnosis of amelanotic melanoma, histological evaluation of affected tissue, and immunohistochemistry in a rabbit.