Gallbladder Carcinoma in a Eurasian Otter (Lutra lutra)

An adult female Eurasian otter (Lutra lutra), introduced with another subject in the National Park of Gran Paradiso (Aosta Valley Region, Italy), was found dead. The necropsy found a mass involving mainly the gallbladder walls with other multicentric masses in the liver and pancreas. In addition to these, through the histological examination, other nodules were detected in the pancreas, with structure similar to gallbladder neoplasm. Histopathology diagnosed it as neoplasia composed of epithelioid cells, forming lobules of tubules and pseudoacini, with a very low mitotic count, discrete cellular pleomorphism, and prominent fibrous stroma. Neoplastic cells demonstrated positive immunoreactivity for cytokeratin and negative immunoreactivity for S100. Gross and histologic lesions and immunohistochemical findings were consistent with a primary gallbladder carcinoma (GBC) of metastatic type. GBC is a rare neoplasm in both humans and animals, sometimes associated with cholelithiasis and cholecystitis, with few reports in the veterinary literature especially in cattle, pigs, dogs and cats. To the best of our knowledge, this is the first report of GBC in a Eurasian otter.