Abstract

Squamous cell carcinoma (avian keratoacanthoma) is a neoplastic skin lesion of unknown etiology, that has been well described in birds, including broiler chickens, parrots, common stork, raptors, and different species of aquatic birds. In some studies, the possibility of the involvement of pox viruses in the cause of SCC was reported.

Our case concerned a squamous cell carcinoma of the foot, diagnosed in an adult pelican maintained in captivity. Grossly, a cauliflower-like mass with irregular edges was found on the ventral surface of the foot. The large ulcerated mass caused severe lameness, leading to weight loss and emaciation; leucocytosis and anemia due to continue bleeding of the mass were also noted.

Histologically, the tumor consisted of irregular cords of pleomorphic epithelial cells that showed a disorganized pattern of growth and invaded the adjacent tissues. In some of these cells, pale eosinophilic intracytoplasmic inclusions, characteristic of virus, were seen. Additionally, keratinized epithelial cells and moderate numbers of keratin pearls were readily observed. The mitotic index was low, and, although the tumor was locally invasive, we found no evidence of vascular invasion or metastasis. Tumor showed a strong and diffuse positive immunostain for cytokeratin of different molecular weight, and high nuclear expression of proliferating cell nuclear antigen (PCNA). The morphology of the neoplasm and the immunohistochemistry allowed us to confirm our diagnosis.

This is the first report of a SCC in a pelican. Although the etiology of the carcinoma may have been secondary to chronic focal trauma, the possibility that a latent or chronic form of fowlpox should be considered in the pathogenesis of the lesion.