Malignancies of the small bowel are almost always treatable and some may be curable. Their prognosis and treatment depend on the cellular origin.
Types Small intestinal malignancies are generally adenocarcinomas, sarcomas, carcinoid tumors and lymphomas.
The most common of all—half of small intestine tumors—are adenocarcinomas that develop in glandular tissue . Most people with adenocarcinomas have metastases to the lymph nodes , liver or peritoneum (abdominal lining) at the time of diagnosis.
Sarcomas are slow-growing tumors that account for 11 percent of small bowel cancers. Sarcomas can develop in any soft tissue such as fat cells (liposarcoma), blood vessels (angiosarcoma) or nerves (neural sarcomas, neurofibrosarcomas or malignant schwannomas, which develop from the nerve sheath, most commonly in the ileum). But 75 percent of the sarcomas, called leiomyosarcomas, originate in the smooth muscles encircling the bowel. These malignancies may reach a large size before diagnosis (many are larger than 2 in. (5 cm)). Only a third of smooth muscle tumors are malignant.
Carcinoid tumors account for 30 percent of small bowel malignancies. They are often small (usually 1/2 to 1 1/2 in./1 to 5 cm in diameter) and slow growing. There may be multiple lesions and may be present for years ( see "Carcinoids of the Gastrointestinal Tract" ).
