Intestinal cancer is a malignancy that develops in the lining or walls of the intestines, which include the small intestine and the large intestine (colon and rectum). While colorectal cancer is one of the most common cancers in the United States, with nearly 148,000 new cases reported in 2022, small intestine cancer is surprisingly rare, accounting for just 0.6% of all cancers diagnosed in the country. Despite the small intestine making up the largest segment of the digestive system, only about 3% of all gastrointestinal cancers originate there.
Small Intestine vs. Large Intestine Cancer
The distinction between small and large intestine cancer matters because these are very different diseases in terms of frequency, behavior, and treatment. Colorectal cancer (large intestine) is far more common and has well-established screening programs, like colonoscopies, that catch precancerous growths early. Small bowel cancer, by contrast, is much harder to detect because the small intestine is long, deeply coiled, and difficult to reach with standard scopes.
When people search for “intestinal cancer,” they may be looking for information on either type. Colorectal cancer has its own extensive body of guidance, so the rest of this article focuses primarily on small intestine cancer, which is less well known and often diagnosed later.
Types of Small Intestine Cancer
There are about 40 different subtypes of small intestine cancer, but four account for the vast majority of cases:
- Adenocarcinoma makes up roughly 30% to 40% of small bowel cancers. These tumors start in the cells that line the inside of the intestine and are most common in the duodenum, the section closest to the stomach.
- Carcinoid tumors (also called neuroendocrine tumors) account for about 35% to 42% of cases. They grow from hormone-producing cells and most often appear in the ileum, the last section of the small intestine. They tend to grow more slowly than adenocarcinomas.
- Lymphoma represents 15% to 20% of small bowel cancers. It starts in immune system cells within the intestinal wall and is most common in the ileum and jejunum (the middle section).
- Sarcoma accounts for 10% to 15% of cases. These tumors develop in the muscle or connective tissue of the intestinal wall and are more evenly distributed throughout the small bowel.
Symptoms to Watch For
Small intestine cancer is notoriously difficult to catch early because its symptoms overlap with many common, benign digestive problems. The most frequently reported signs include abdominal pain or cramping, unexplained weight loss, nausea and vomiting, and fatigue. Some people notice blood in their stool, which can appear bright red or dark and tarry depending on where the bleeding originates.
Carcinoid tumors can cause a distinctive symptom called skin flushing, along with watery diarrhea, because these tumors sometimes release hormones into the bloodstream. Tumors in the duodenum may cause jaundice, a yellowing of the skin and eyes, if they block the bile duct.
One of the more serious complications is bowel obstruction. As a tumor grows, it can physically block the passage of food and waste through the intestine, or it can interfere with the nerves that control intestinal movement. Early obstruction may cause mild, intermittent cramping and bloating. As it progresses, symptoms intensify: frequent vomiting, extreme abdominal swelling, inability to pass gas, and severe pain. A complete obstruction is a medical emergency.
Risk Factors and Genetic Links
Most small intestine cancers develop without a clear inherited cause, but certain conditions significantly raise risk. Crohn’s disease, which causes chronic inflammation in the small bowel, is one of the strongest risk factors for small intestine adenocarcinoma. Celiac disease, an autoimmune reaction to gluten, has also been linked to increased risk, particularly for intestinal lymphoma.
Several inherited genetic syndromes play a role as well. Familial adenomatous polyposis (FAP) causes hundreds to thousands of polyps to form in the intestinal lining, some of which can become cancerous. Lynch syndrome, also known as hereditary nonpolyposis colorectal cancer, is the most common inherited cause of colorectal cancer, responsible for up to 5% of all colorectal cases, and it also raises the risk of small bowel adenocarcinoma. Peutz-Jeghers syndrome, though rarer, involves distinctive polyps in the small intestine that carry cancer risk.
How Intestinal Cancer Is Diagnosed
Diagnosing small bowel cancer has historically been challenging because conventional endoscopes can only reach the upper and lower ends of the digestive tract. Newer technologies have changed this. The typical diagnostic process starts with a three-phase CT scan. If imaging reveals a mass, thickened intestinal wall, or narrowing, more specialized tools come next.
Capsule endoscopy involves swallowing a pill-sized camera that takes thousands of images as it travels through the digestive tract. It’s painless, performed on an outpatient basis, and has a high rate of detecting abnormalities. However, it can’t take tissue samples. When a biopsy is needed, or when the capsule findings need a closer look, balloon-assisted endoscopy allows a doctor to navigate deep into the small bowel using an inflatable overtube system. This technique can both diagnose and sometimes treat lesions. CT enterography, a specialized scan where you drink a bowel-cleansing solution before imaging, provides particularly detailed views of the intestinal wall and can detect masses that standard CT might miss.
Staging and What It Means
Small bowel adenocarcinoma is staged using the TNM system, which evaluates three factors: how deeply the tumor has invaded the intestinal wall (T), whether cancer has spread to nearby lymph nodes (N), and whether it has reached distant organs (M). Early-stage tumors (stage I and II) are confined to the intestine without lymph node involvement. Stage III means the cancer has reached nearby lymph nodes, and stage IV indicates it has spread to distant sites like the liver or lungs.
About 32% of small intestine cancers are caught while still localized. Another 33% are found after spreading to regional lymph nodes, and 27% are not diagnosed until the cancer has already metastasized. These proportions reflect the difficulty of early detection in an organ that doesn’t have routine screening.
Treatment Approaches
Surgery is the primary treatment for small intestine cancer that hasn’t spread widely. The goal is to remove the tumor along with surrounding lymph nodes. What the surgery looks like depends on where the tumor is located. Tumors in the duodenum often require a more complex procedure that removes part of the pancreas and stomach along with the affected intestine. Tumors in the jejunum or ileum are typically treated with removal of the affected segment, sometimes including a portion of the colon if the tumor is near the junction.
Even after successful surgery, recurrence rates remain high. Chemotherapy after surgery is sometimes recommended for more advanced cases, particularly stage III disease. The regimens used are adapted from colorectal cancer treatment, since small bowel cancer is too rare for large dedicated trials.
For cancers that have spread or can’t be surgically removed, chemotherapy combinations can shrink tumors and extend life. In clinical studies, common two-drug regimens achieved tumor shrinkage in roughly 45% to 50% of patients. Some patients with specific tumor characteristics may benefit from immunotherapy, particularly those whose tumors have a feature called microsatellite instability, which makes them more responsive to drugs that activate the immune system.
Survival Rates by Stage
Five-year survival rates for small intestine cancer vary dramatically by how far the disease has progressed at diagnosis. When the cancer is still confined to the intestine, the five-year relative survival rate is 85.6%. If it has spread to nearby lymph nodes, that drops to 79.6%, which is still relatively favorable. Once the cancer has metastasized to distant organs, the five-year survival rate falls to 46.6%. These numbers, based on data from 2015 to 2021, represent averages across all small bowel cancer types. Individual prognosis depends on the specific tumor type, location, overall health, and how the cancer responds to treatment.