Intrahepatic Cholangiocarcinoma With Pulmonary Metastasis in a Rhesus Macaque ( <i>Macaca mulatta</i> )

A 28-year-old, female Rhesus macaque (<i>Macaca mulatta</i>) was lethargic and inappetent despite supportive treatment. Euthanasia was elected. Necropsy revealed numerous nodules in the liver and lung. Microscopically, the liver and lung were multifocally effaced by a poorly demarcated proliferation of neoplastic epithelial cells arranged in irregular and tortuous tubules and nests. Neoplastic cells showed positive immunolabeling for CK7 and negative immunolabeling for Hep-Par1. Findings in the liver and lung were consistent with cholangiocarcinoma, which is a rare neoplasm in non-human primates and has not been previously reported as a spontaneous finding in laboratory-kept Rhesus macaques. Rhesus macaques exhibit increased tumor incidence with age similar to humans, emphasizing the need for a comprehensive understanding of spontaneous neoplasia in this species.