The duodenum is the C-shaped, first part of the small intestine, which begins at the pylorus that controls the outlet of the stomach and ends at the duodenojejunal flexure where it becomes the jejunum. The duodenum is fixed in position in the retroperitoneal space. It is intimately attached to the head of the pancreas and pancreatic uncinate process.
Duodenal tumours are rare and varied. They may arise from the duodenal mucosal epithelium, endocrine cells of the duodenum, pacemaker cells called interstitial cells of Cajal or the duodenal muscle cells. Tumours in the duodenum may also have extended into the duodenum from the ampulla of Vater. These tumours may have also invaded through the duodenal wall from the pancreatic head or pancreatic uncinate process. Tumours that arise from the duodenal mucosa and the ampulla of Vater termed "adenomas" if they are benign. Adenocarcinomas are malignant. Adenomas, however, can undergo malignant transformation to adenocarcinoma.
Tumours that arise from endocrine cells are called neuroendocrine tumours. The most common functioning neuroendocrine tumours are gastrinomas. Microscopic submucosal tumours that secrete excessive amounts of the hormone gastrin and may be solitary or multiple. The excessive gastrin secretion results in excessive secretion of hydrochloric acid by the stomach, which results in the Zollinger-Ellison syndrome characterized by peptic ulceration of the stomach and duodenum and diarrhoea. Some neuroendocrine tumours (NETs) do not secrete excessive amounts of hormones and are known as non-functioning NETs. Most NETs occur sporadically, but some are associated with inherited genetic mutations that result in various syndromes (Multiple Endocrine Neoplasia Syndromes 1 and 2, Von Hippel-Lindau Syndrome and Neurofibromatosis).NETs are malignant, but usually of low-grade malignancy. Sometimes a tiny duodenal primary NET is only found after being found to have isolated or diffuse metastases (secondaries), which may be much larger than the primary tumour(s). Occasionally, however, NETs are high-grade malignant tumours.
Tumours that arise from the pacemaker cells are known as Gastro-Intestinal Stromal Tumours (GISTs). These vary from small submucosal tumours to massive tumours that invade adjacent structures (stomach, pancreas, kidney, colon etc.) and from low-grade malignant to high-grade malignant. About 80% of cases are associated with a mutation in the KIT gene. About 10 per cent of cases are associated with a mutation in the PDGFRA gene. At the same time, a few affected individuals have mutations in other genes. Mutations in the KIT PDGFRA genes are associated with both familial and sporadic GISTs.
Soft tissue sarcomas that arise from mesenchymal (connective tissue, muscle, etc.) may also occur in the duodenum, and small intestine and are usually only diagnosed when they have reached enormous sizes.
Treatment with curative intent involves surgery, with or without some form of medical therapy.
Medical therapy for low-grade neuroendocrine tumours may include a somatostatin analogue (octreotide/lanreotide). GISTs are treated with a group of drugs called tyrosine kinase inhibitors. Imatinib, sunitinib and regorafenib etc. are used for tumours that are resistant to imatinib.
Palliative treatments, to control symptoms and prolong survival, are many and varied, but generally involve systemic treatments supplemented with local therapies including surgery, radiotherapy and endoscopic and percutaneous interventions.