ON THIS PAGE: You will find some basic information about this disease and the parts of the body it may affect. This is the first page of Cancer.Net’s Guide to Small Bowel Cancer. To see other pages, use the menu on the side of your screen. Think of that menu as a roadmap to this full guide.
Small bowel cancer starts when cells in the lining of the small bowel (also called the small intestine) change and grow uncontrollably, forming a mass called a tumor. A tumor can be benign (noncancerous) or malignant (cancerous, meaning it can spread to other parts of the body). These changes can take a long time to develop. Both genetic and environmental factors can cause such changes, although the specific causes of small bowel cancer are generally not well understood.
About the small bowel
The small bowel is part of the digestive system, and its function is to break down food and nutrients to be absorbed into the body. It links the stomach to the large intestine (colon). The small bowel is divided into three parts: the duodenum, the part closest to the stomach; the jejunum, the middle portion; and the ileum, the bottom section, which connects to the large intestine, or colon. The small bowel is approximately 15 feet long, folds many times to fit inside the abdomen, and makes up three-quarters of the digestive system.
Types of small bowel cancer
There are five main types of small bowel cancer:
Adenocarcinoma. Adenocarcinoma is the most common type of small bowel cancer, usually occurring in the duodenum or jejunum. Adenocarcinoma begins in the gland cells of the small bowel.
Sarcoma. Small bowel sarcoma is generally a leiomyosarcoma (a tumor that arises in the muscle tissue that makes up part of the intestine) and most often occurs in the ileum. Learn more about sarcoma.
Gastrointestinal stromal tumor (GIST). GIST is an uncommon tumor that is believed to start in cells found in the walls of the gastrointestinal (GI) tract, called interstitial cells of Cajal (ICC). GIST belongs to a group of cancers called soft tissue sarcomas. Learn more about gastrointestinal stromal tumors.
Carcinoid tumor. Carcinoid tumors are classified as neuroendocrine tumors (tumors that originate in the hormone-producing cells of various organs) and generally occur in the ileum. Learn more about carcinoid tumors.
Lymphoma. Lymphoma is a cancer of the lymph system, which is part of the body’s immune system. Lymphoma that occurs in the small bowel usually occurs in the jejunum or ileum and is most commonly non-Hodgkin lymphoma. Learn more about non-Hodgkin lymphoma.
To continue reading this guide, use the menu on the side of your screen to select another section.