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Hepatocellular Carcinoma in Black-tailed Prairie Dogs (Cynomys ludivicianus): Tumor Morphology and Immunohistochemistry for Hepadnavirus Core and Surface Antigens

Northwest ZooPath, Monroe, WA (MMG, JTR); and College of Veterinary Medicine, Cornell University, Ithaca, NY (IT, BCT)

From 1994 to 2002, tissues from 61 prairie dogs were submitted to Northwest ZooPath for histopathology. Of these, 12 (20%) had hepatocellular carcinoma (HCC). Three were pets submitted from private veterinary practices. The others were submitted from zoos in the United States. All were adults, ranging from young adult to 7 years of age, with average age of 5.1 years. The most common clinical signs were weight loss, lethargy, palpable abdominal mass, and respiratory difficulty. All tumors were well-differentiated HCCs in which four histologic patterns were recognized. The trabecular pattern was predominant in nine tumors, and the pseudoglandular pattern was predominant in two tumors. The pelioid pattern was also represented in eight tumors. A papillary pattern was present in one case. In seven cases vacuolar change resembling lipidosis was present in the neoplastic hepatocytes of both primary and metastatic tumors. Anaplasia was mild to moderate in most tumors, but a marked degree of anaplasia was noted in the metastatic foci of the case with papillary differentiation. Metastasis to lung was noted in five cases. One of these also had metastasis to the spleen, and another had metastasis to heart and mediastinum. In two cases there was concurrent hepatitis and in two cases, cirrhosis. All tumors and nonneoplastic liver stained negatively for woodchuck hepatitis virus surface and core antigens, and orcein and Victoria blue positive staining of hepatocytes typical of hepadnavirus infection in humans and woodchucks was not present. HCC is apparently common in captive prairie dogs. The hepatic neoplasia observed in prairie dogs was similar to that associated with hepadnaviral infection in humans, woodchucks, and ground squirrels, but no direct evidence of hepadnaviral infection was detected. The rate of metastasis in captive prairie dogs was higher than that reported in woodchucks.

Key words: Black-tailed prairie dogs; Cynomys ludivicianus; hepadnavirus; hepatocellular carcinoma; immunohistochemistry; Marmota monax; morphology; woodchucks.

Request reprints from Dr. M. M. Garner, Northwest ZooPath, 654 W. Main, Monroe, WA 98272 (USA). E-mail: zoopath{at}aol.com