Malignant Melanoma in the Penguin: Characterization of the Clinical, Histologic and Immunohistochemical Features of Malignant Melanoma in Ten Individuals from Three Species of Penguin
Malignant melanomas are aggressive neoplasms that are relatively common in humans, dogs and horses, and rare in avian species.1,2 Melanocytic neoplasms in 5 macaroni penguins (Eudyptes chrysolophus), 3 rock hopper penguins (Eudyptes chrysocome) and 2 Humboldt penguins (Spheniscus humboldti) are described. The average age of onset was 20.3 years, and the most common sites were the skin of the foot/ankle and near the edge of the beak. Tumors started as smooth, flat lesions and became raised and ulcerated over time. Two tumors less than 17 mm in greatest dimension were cured by complete surgical excision, while tumors larger than 20 mm were associated with metastatic disease. The liver was the most common site of metastasis and was often largely effaced by neoplastic cells; despite this, serum AST values only became elevated weeks to days prior to death. Neoplastic cells varied from round to polygonal to spindloid, contained abundant intracytoplasmic melanin, and were arranged in clusters or nests, often within the overlying epithelium. Cellular indices of malignancy included anisokaryosis, multiple prominent nucleoli, intranuclear pseudoinclusions, and multinucleated cells. Immunohistochemical labeling with four common melanocytic markers (PNL2, Melan-A, S-100, and HMB-45) was performed on tissues from 8 of 10 affected penguins and included both primary and metastatic tumors. None of the tumors labeled with Melan-A or S-100. Four of 6 primary tumors showed positive labeling for HMB-45 and all showed positive labeling for PNL-2. Three different molecular diagnostic testing methods were performed to look for viral particles and results were negative.
Case materials were shared by three institutions including the Philadelphia Zoo, Louisville Zoo, and Indianapolis Zoo. I’d also like to thank the Veterinary Staff and Penguin Staff at the Detroit Zoo.
1. Conroy, J. D. 1967. Melanocytic tumors of domestic animals. Arch. Dermatol. 96:372–380.
2. Smith, S.H., M.H. Goldschmidt, and P.M. McManus. 2002. A comparative review of melanocytic neoplasms. Vet. Pathol. 39: 651–678.