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A risk factor is anything that changes your chance of getting a disease such as cancer. Different cancers have different risk factors. Some risk factors, like smoking, can be changed. Others, like a person’s age or family history, can’t be changed.

But risk factors don’t tell us everything. Having a risk factor, or even several, does not mean that a person will get the disease. And many people who get the disease may have few or no known risk factors.

Because small intestine adenocarcinoma is so uncommon, risk factors for this disease have been hard to study. Some of the known risk factors include:

Sex

Small intestine cancer occurs slightly more often in men than in women.

Age

Cancers of the small intestine tend to occur more often in older people. They are most often found in people in their 60s and 70s.

Race/ethnicity

In the United States, African Americans are affected more often by these cancers than people of other races/ethnicities.

Smoking and alcohol use

Some studies have found an increased risk with either smoking or drinking alcohol, but not all studies have found this.

Diet

Some research has suggested that diets high in red meat and salted or smoked foods might raise the risk of small intestine cancer.

Celiac disease

For people with celiac disease, eating gluten (a protein that is found in wheat and some other types of grain) causes the body's immune system to attack the lining of the intestines. People with celiac disease have an increased risk of a certain kind of lymphoma of the intestine called enteropathy-associated T-cell lymphoma. They may also have an increased risk of small intestine cancer.

Colon cancer

People who have had colon cancer have an increased risk of getting cancer of the small intestine. This could be due to shared risk factors.

Crohn's disease

Crohn's disease is a condition in which the immune system attacks the gastrointestinal (GI) tract. This disease can affect any part of the GI tract, but it most often affects the lower part of the small intestine. People with this condition have a much higher risk of small intestine cancer (particularly adenocarcinoma). These cancers are most often seen in the ileum (the last part of the small intestine, near the colon).

Inherited syndromes

People with certain inherited conditions have a higher risk of small intestine cancer (mainly adenocarcinoma).

Familial adenomatous polyposis (FAP)

In this condition, many (often hundreds) of polyps develop in the colon and rectum. If the colon isn’t removed, one or more of these polyps will become cancerous. Polyps can also develop in the stomach and the small intestine, and they can lead to cancers in these areas. In FAP, most small intestine cancers are found in the duodenum. This condition is caused by an abnormal change (mutation) in the APC gene, and is discussed more in Colorectal Cancer.

Lynch syndrome (hereditary nonpolyposis colorectal cancer, or HNPCC)

In most cases, this disorder is caused by a defect in one of several mismatch repair (MMR) genes, such as MLH1, MSH2, MSH6, PMS1, or PMS2. Having an abnormal version of any one of these genes reduces the body’s ability to repair damage to its DNA. This results in an increased risk for cancer of the colon and small intestine, as well as a high risk of endometrial and ovarian cancer. This condition is also discussed in Colorectal Cancer.

Peutz-Jeghers syndrome (PJS)

People with this condition develop polyps in the stomach and intestines, as well as in other areas including the nose, the airways of the lungs, and the bladder. They can also have dark freckle-like spots on the lips, inner cheeks and other areas. PJS can increase the risk of many types of cancer, including small intestine adenocarcinoma. This syndrome is caused by mutations in the STK11 (LKB1) gene.

MUTYH-associated polyposis

People with this syndrome develop colon polyps which will almost always become cancerous if the colon is not removed. They also can get polyps in the small intestine and have an increased risk of small intestine cancer. People with this syndrome can also get cancers of the skin, ovary (in women), and bladder. This syndrome is caused by mutations in the MUTYH gene.

Cystic fibrosis (CF)

People with this condition have severe lung problems. Often, in someone with CF, the pancreas cannot make the enzymes that break food down so that it can be absorbed. People with CF have an increased risk of small intestine cancer. A child must have 2 abnormal copies of the CFTR gene (one from each parent) to get this disease.