Abstract
An 11-year-old male common marmoset (Callithrix jacchus) presented with chronic, progressive weight loss and diarrhoea. Response to treatment with nutritional supplementation, antibiotics and immunosuppressants was modest and transient, and the animal was humanely euthanized. At necropsy, the proximal 8 cm of small intestine was diffusely pale with transmural thickening. The lungs contained coalescing tan, firm nodules measuring up to 4 mm in diameter. Histological examination revealed infiltrative mucinous adenocarcinoma of the duodenum with extensive metastases to the lungs, liver and left parapatellar adipose tissue. The mucinous matrix secreted by the primary and metastatic lesions was strongly periodic acid-Schiff positive. Warthin Starry staining for spirochaetes was negative. Pancytokeratin expression was attenuated in the primary tumour as well as in the metastases, which correlated to a poorly differentiated phenotype. To the authors' knowledge, this is the first report of a proximal duodenal adenocarcinoma with extensive metastatic disease in a common marmoset.