Abstract
A 28-year-old, female Rhesus macaque (Macaca mulatta) 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.
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