Duodenal polyposis. Endoscope view of a tubular polyp (left) on the lining the duodenum (part of the small intestine). The polyp is an adenoma, a benign tumour, in this case caused by a genetic disease called Familial Adenomatous Polyposis (FAP). Most such polyps are without symptoms, but they may cause bleeding and anaemia. Some may become malignant (cancerous), and so require careful monitoring.