A neuroendocrine neoplasm that involves the duodenum. The disease is Monarch Disease Ontology entry MONDO_0024500 (duodenal neuroendocrine neoplasm). Also known as: duodenum NET, duodenum neuroendocrine neoplasm, duodenum neuroendocrine tumor, duodenum neuroendocrine tumor, well differentiated, low or intermediate grade, duodenum neuroendocrine tumour, neuroendocrine neoplasm of duodenum.