The small intestine, or small bowel, lies between the stomach and the colon. The small intestine is about 20 feet long. Its primary function is to digest and absorb nutrients. The small intestine makes up more than 70% of the length and 90% of the surface area of the gastrointestinal (GI) tract.
The most common cancerous (malignant) tumors of the small intestine include adenocarcinoma, carcinoid, gastrointestinal stromal tumor, lymphoma, and cancer that has spread from other places in the body.
In industrialized countries, adenocarcinomas occur most often.
In developing countries, lymphomas are much more common.
All these tumors have the potential to invade the bowel wall, move into adjoining lymph nodes, and spread to distant organs (metastasize).
Each year, U.S. doctors diagnose about 1,200 malignant small intestine tumors. This is a small number relative to the frequency of tumors in other parts of the GI tract.
It's been thought the liquid nature of the contents of the small intestine may be less irritating to the mucosa, the innermost lining of the small bowel.
The less time it takes for food to move through the small bowel may reduce exposure to cancer-causing.
Other factors that might limit the impact of potential cancer-causing substances include the following:
A low bacteria count in the GI tract
A large lymphoid tissue component in the wall of the small intestine
An alkaline pH inside the small intestine
The presence of the enzyme benzpyrene hydroxylase
Adenocarcinoma of the small bowel is associated with the following underlying conditions:
Crohn's disease -- An inflammation in the small intestine. Crohn's disease usually occurs in the lower part of the small intestine, called the ileum. The inflammation extends deep into the lining of the affected organ, causing pain and making the intestines empty frequently, resulting in diarrhea.
Familial polyposis syndromes -- An inherited disease in which the large bowel becomes carpeted by polyps of various dimensions during the second or third decade of life. If untreated, the disease invariably leads to cancer of the colon or rectum. Celecoxib (Celebrex) has been FDA approved for this disorder.
Peutz-Jaegher syndrome -- a syndrome characterized by increased skin pigmentation around the nose, lips, gums, hands, and feet, which is also associated with polyps. Up to 50% of people with this disease will develop cancer at an average age of 50.
Cancer is 50 times more common in the large bowel than in the small bowel. Risk factors in the general population include the following:
Consumption of salted or smoked meats and fish
Heavy sugar intake
Risk factors for developing cancer of the small intestine in Crohn's disease include the following:
Long duration of disease
Associated fistulous disease: A fistula is an abnormal tube that passes from one surface to another, such as from the colon to the skin.
Surgical removal of part of the bowel
The risk of developing small intestinal cancer is six times greater for people with Crohn's disease compared to the general population.
Lymphoma of the small intestine is associated with celiac disease and weakened immune systems, such as occurs with AIDS.