Spontaneous hepatocellular carcinoma in laboratory-reared degus (Octodon degus): histopathological and immunohistochemical characterization.

The degu (Octodon degus), a highly intelligent rodent with unique communication abilities, has been used in various research fields. However, reports on spontaneous lesions in degus are limited. During routine examinations, we incidentally observed hepatic nodular lesions in laboratory-reared degus maintained at the University of Miyazaki. We aimed to investigate the prevalence and histopathological characteristics of hepatic nodular lesions in degus. The prevalence of these lesions increased with age, but no sex-related differences were observed. No gross abnormalities were noted in any organ other than the liver. Serum biochemistry revealed significantly higher aspartate aminotransferase levels in animals with hepatic nodules than in those without nodules. Histopathologically, the nodules were sharply demarcated from the normal hepatic parenchyma without fibrous encapsulation, and showed loss of lobular architecture and portal triads, along with markedly thickened hepatic cords. The nodular cells expressed arginase-1 and exhibited abundant clear cytoplasm, moderate anisocytosis, anisokaryosis, and glycogenated nuclei. Despite rare mitotic figures, the Ki67 labeling index of the neoplastic cells was significantly higher than that of normal hepatocytes. There was no evidence of epithelial mesenchymal transition in the lesions. Collectively, these hepatic nodules were diagnosed as spontaneously occurring, well-differentiated hepatocellular carcinomas. This is the first report to compile multiple cases of spontaneous hepatocellular carcinoma in degus. This study provides valuable background pathological information and supports the potential utility of degus as a laboratory animal model in hepatocellular neoplasia.