Light micrograph section through human stomach tissue showing duodenal polyps. The duodenum is the first part of the small intestine. After foods mix with stomach acid, they move to the duodenum, where they mix bile from the gallbladder and digestive juices from the pancreas. Duodenal polyps are found in people who have an endoscopy to look into the stomach. The most common cause of stomach polyps is chronic stomach inflammation, also known as gastritis. The condition can cause the formation of hyperplastic polyps and adenomas. Hyperplastic polyps are unlikely to become cancerous, although those larger than 1cm carry a greater risk.