Although the digestive tract is one of the more common places cancer arises in the body (colorectal cancer, for example, is one of the four most common types of cancer in the United States), it’s unusual for cancer to affect the small intestine. 

This may be surprising, since the small intestine makes up 90% of the digestive tract. But only 3 to 5% of digestive tract cancers occur in the small intestine.  

Small intestine cancers are difficult to diagnose. The small intestine is a body part that isn’t screened regularly, unlike the colon for which patients undergo regular screening colonoscopies. And people with small intestine cancer often don’t notice symptoms until their disease has progressed. When people do experience symptoms, they’re often vague ones that could indicate many other problems related to the digestive system.  

Small intestine cancer is slightly more common among men than women, and it’s typically diagnosed in people who are 65 and older.  

“The management of small intestine adenocarcinoma is largely extrapolated from colorectal cancer, which has had numerous advances over the past decade,” says Smilow Cancer Hospital oncologist Michael Cecchini, MD, a specialist in gastrointestinal cancers. “Like colorectal cancer, when the cancer is localized at the time of diagnosis, the majority of patients will be cured.” 

Small intestine cancer is the umbrella term used for a number of different types of cancers that affect different parts of the small intestine.  

It’s a fairly uncommon type of cancer. Only about 11,000 Americans are diagnosed with small intestine cancer each year, accounting for fewer than 1% of all new cancer diagnoses.  

There are several common types of small intestine cancer including adenocarcinoma, neuroendocrine tumors, lymphomas, and gastrointestinal stromal tumors (a rare type of sarcoma). The most common type of tumor to occur in the small intestine is a neuroendocrine tumor. The next most common type is adenocarcinoma. Each of the cancers of the small intestine are treated very differently.  

Most adenocarcinomas occur in the duodenum, the first stretch of the small intestine that connects to the stomach. It’s also possible for adenocarcinomas to form in other parts of the small intestine, including the jejunum or the ileum—the middle and last portions of the small intestine.

When certain cells within the small intestine mutate or change, they may begin to multiply uncontrollably, forming tumors or cancer.  

One theory on why this may happen is that chronic inflammation within the small intestine has been linked with mutation and excessive cell reproduction. Over time, inflammation is believed to cause changes to cells within the small intestine, leading the cells to mutate and multiply uncontrollably.  

Conditions like Crohn’s disease, ulcerative colitis, celiac disease, and other digestive conditions may cause chronic inflammation of the small intestine. It may also be caused by smoking and alcohol consumption, as well as by certain dietary habits, such as eating a lot of red meat or saturated fat.

Many people don’t have symptoms during the early stages of disease. Those who do may experience:

• Abdominal pain or cramping
• Unexplained weight loss
• Bleeding in the gastrointestinal tract, leading to blood in bowel movements (which may appear as fresh blood or dark-colored stool)
• Indigestion
• Bloating
• Nausea and/or vomiting
• Diarrhea
• A change in bowel habits
• Small bowel obstruction
• Loss of appetite
• Weakness
• Jaundice
• Anemia
• Trouble breathing

People may be at higher risk if they have, or have had, these medical conditions:

• Crohn’s disease
• Celiac disease
• Peptic ulcers
• Colorectal cancer
• A family history of conditions that raise the risk of intestinal cancer, including familial adenomatous polyposis, Lynch syndrome, and Peutz-Jeghers syndrome
• Cystic fibrosis
• HIV or AIDS
• An organ transplant
• Previous radiation therapy
• Surgery to remove the gallbladder

Additionally, eating the following types of food may raise a person’s risk of small intestine adenocarcinoma:

• Red meat
• Smoked meat
• Salt-cured meat
• Saturated fat
• Sugar

Consuming alcoholic beverages and smoking cigarettes are additional habits linked to small intestine cancer.

The fact that many people don’t experience symptoms means that these cancers tend to be discovered late, since doctors aren’t looking for them. But when there are problems suggestive of the condition, doctors ask questions to learn about the person’s medical history and symptoms.  

Doctors will want to know if the patient has Crohn’s disease, celiac disease, or other digestive conditions. They will ask if there is a personal or family history of digestive disease cancer or inherited conditions, such as Lynch syndrome, which raise the risk of these cancers. They’ll also ask about diet and lifestyle habits, to find out if the patient consumes a lot of beef or cured meats, and to learn how much alcohol they drink—and whether they smoke.  

During a physical exam, the doctor will press on the abdomen to see if it feels distended or bloated, or to see if the person experiences pain. A doctor may also perform a digital rectal exam to check for bleeding.  

Diagnostic tests to identify or rule out small intestine cancer include:  

• CT scan or MRI are imaging tests that allow doctors to visually examine internal tissues and organs.
  
• Barium X-ray, during which the patient drinks a beverage containing barium, so that abnormal areas within the small intestine will stand out on X-ray images
  
• Capsule endoscopy, during which the patient swallows a pill containing a camera, which is used to examine the inside of the small intestine
• Enteroscopy, during which a long, thin tube with a camera on the end is inserted into the mouth or anus, to view the inside of the small intestine; a special balloon attached to the tube is inflated to help move the tube farther along through the intestinal tract.
  
• Endoscopic ultrasonography, during which a long, thin tube with an ultrasound device is inserted into the mouth, down the esophagus to the first section of the small intestine; ultrasound waves can show images of the interior of the digestive system.
• Blood tests to look for cancer markers or other conditions
• Fecal occult blood test, which checks for the presence of blood in the stool

If doctors see a tumor or other signs of cancer, they must biopsy the tissue to make a formal diagnosis. The biopsy is often done with endoscopy. Sometimes, when the tumor is in a location that isn’t reachable by an endoscope, a surgical biopsy is necessary.

Whenever possible, surgery to remove the cancer is the preferred treatment for many types of small intestine cancer, including adenocarcinoma. Typically, doctors remove the tumor, some healthy surrounding tissue, and lymph nodes. Sometimes, when the cancer is in the duodenum, a segment of the pancreas is also removed. Often, people receive chemotherapy after surgery, with or without radiation.  

If small intestine cancer has spread to other body parts, called metastatic disease, the patient may receive chemotherapy or immunotherapy to help the body’s immune system fight the cancer, or a combination of these therapies. Rarely, surgery is sometimes used in treating small intestine adenocarcinoma if it has spread to other body parts.

The earlier that small intestine cancer is diagnosed and treated, the better the outlook is for patients.  

About 85% of people who have localized small instestine adenocarcinomas survive 5 years or more, while for those who have metastatic small intestine adenocarcinomas, the 5-year survival rate drops to 42%.

“The teams at Yale Cancer Center and Smilow Cancer Hospital use a multidisciplinary approach when treating small intestine adenocarcinomas, including surgical oncologists, colorectal surgeons, medical oncologists, radiation oncologists, and gastroenterologists,” says Yale Medicine oncologist and director of the Center for Gastrointestinal Cancers at Smilow Cancer Hospital and Yale Cancer Center Pamela Kunz, MD. “These teams often discuss patients in one of the Gastrointestinal [GI] Tumor Boards to get expert input from multiple specialists. In addition, for patients with metastatic disease, we have teams who specialize in developing and evaluating novel treatments in clinical trials.”