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.
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. All these tumors have the potential to invade the bowel wall, move into adjoining lymph nodes, and spread to distant organs (metastasize).
In industrialized countries, adenocarcinomas occur most often.
In developing countries, lymphomas are much more common.
Each year, U.S. doctors diagnose close to 9,000 malignant small intestine tumors. While the number of cases of small bowel cancer is on the rise, this is a small number relative to the frequency of tumors in other parts of the GI tract. Reasons given include:
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 chemicals.
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
But the number of cases of small bowel cancer in the United States is steadily increasing.
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-Jeghers syndrome -- a syndrome characterized by increased skin pigmentation around the nose, lips, gums, hands, and feet, which is also associated with polyps. The risk of colorectal cancer and cancer of the small bowel is increased in people with this syndrome. The risk for other types of cancer including breast and gallbladder is also increased.
Lymphoma of the small intestine is associated with celiac disease and weakened immune systems, such as occurs with AIDS.
Cancer is about 15 times more likely to be found in the large bowel than in the small bowel. Risk factors in the general population include the following: