Malignant Melanoma in the Penguin: Characterization of the Clinical, Histologic, and Immunohistochemical Features of Malignant Melanoma in 10 Individuals From Three Species of Penguin

Abstract

Malignant melanomas are aggressive neoplasms that are relatively common in penguins compared to other avian species. In this study, the clinical and pathologic characteristics of melanocytic neoplasms in five macaroni (Eudyptes chrysolophus), three rock hopper (Eudyptes chrysocome), and two Humboldt (Spheniscus humboldti) penguins are described. Tumors most commonly occurred in the skin of the foot or hock, and were seen in the subcutaneous muscle, especially near the beak/oral cavity. Gross lesions were usually heavily pigmented, becoming raised and ulcerated over time. Humboldt penguins had a unique presentation, forming variably pigmented, cornified lesions in the inguinal area. Original case materials were obtained from all but two cases, and were assessed to define the characteristics of malignancy, evaluate four immunohistochemical markers for melanoma, and look for factors useful to informing prognosis and clinical decisions. Diagnosis was made histologically, based on morphologic features and pigmentation. Though not necessary for diagnosis, PNL-2 was found to be a useful immunohistochemical marker. HMB-45 showed unreliable positive labelling and S-100, Melan-A and Ki67 were not useful. Several factors were associated with prognosis, including gross surface dimension, mitotic index, depth of neoplastic cell invasion, and degree of surface ulceration. Metastatic spread occurred to the liver, lung, adrenal gland, brain, and bone; all lesions showed positive labelling to PNL-2. The average survival after diagnosis was 7 mo, though complete surgical excision of tumors less than 2.0 cm was curative in two cases and radiation therapy prolonged survival in one penguin. The underlying pathogenesis associated with the high prevalence of melanocytic neoplasms in captive penguins could not be identified. Three different molecular methods were performed to look for viral particles and results were negative. Advanced age is the most probable associated risk factor; ultraviolet light and chlorine exposure, viral induction, and genetic predisposition were ruled out or considered unlikely.

Malignant Melanoma of the Syrinx and Liver in an African Grey Parrot (Psittacus erithacus erithacus)

“…16 Ten penguins were identified in that report, and metastasis was found in every animal with a tumor larger than 2 cm in diameter. The World Health Organization classification system for canine oral malignant melanoma classifies any tumor smaller than 2 cm in diameter as a grade I tumor.…”

“…In a penguin with melanoma near the naris, radiation therapy was attempted. 16 The tumor in that bird ultimately regressed, but metastatic lesions arose 29 months later. Radiation therapy with oral antitumor drugs have been previously attempted in a thick-billed parrot with stage IV malignant melanoma, as described by the World Health Organization staging for canine oral melanoma.…”

“…Melanomas have been reported in the following avian species: African grey parrot, 3 thick-billed parrot (Rhynchopsitta pachyrhyncha), 4 umbrella cockatoo (Cacatua alba), 5 budgerigar (Melopsittacus undulatus), 6 zebra finch (Taeniopygia guttata), 7 lesser black-backed gull (Larus fuscus), 8 muscovy (Cairina moschata) and Peking (Anas platyrhynchos) duck cross, 9 Mandarin duck (Aix galericulata), 10 combed duck (Sarkidiornis melanotos), 11 southern Bahama pintail duck (Anas bahama bahamensis), 12 red-tailed hawk (Buteo jamaicensis), 13 merlin (Falco columbarius), 14 rock hopper penguin (Eudyptes chrysocome), 15,16 macaroni penguin (Eudyptes chrysolophus), 13,16 and Humboldt penguin (Spheniscus humboldti). [16][17][18] To our knowledge, no previous case of avian malignant melanoma affecting the syrinx has been described. Melanomas in psittacine birds have been found to affect multiple organ systems and to be markedly malignant, featuring widespread distribution in tissues, aggressive local invasiveness, and cellular pleomorphism.…”

Diagnosis of Retrobulbar Round Cell Neoplasia in a Macaroni Penguin (Eudyptes chrysolophus) Through Use of Computed Tomography

“…Two cases of malignant melanoma have been reported, one of which was also in a macaroni penguin. [12][13][14] There are three reports of round cell tumors of lymphoid origin in penguins. Malignant lymphoma of T-cell origin was found in a Humboldt penguin.…”

“…20 Although melanoma has been reported in birds, including a case in a macaroni penguin, the neoplastic round cells in this case did not contain melanin granules nor did they label with an IHC cocktail for melanoma cell-surface markers designed for canine melanomas, 21 which has anecdotally labeled melanomas in other penguins. 12 Immunohistochemistry has been used successfully in birds, including penguin species, to characterize lymphomatous neoplastic cells as either T-cell or B-cell in origin. 15 In a great horned owl (Bubo virginianus) with disseminated lymphoma, the neoplastic cells were largely CD3-positive and were presumed to be of T-cell origin.…”