Small intestine cancer, also known as small bowel cancer, is one of the rarest forms of cancer affecting the digestive system, accounting for only about 3% of all gastrointestinal cancers in the United States. Despite its rarity, understanding this disease is crucial because its symptoms often appear vague and can be easily mistaken for other, more common conditions, leading to delays in diagnosis and treatment.

Epidemiology

Small intestine cancer is an uncommon disease compared to other cancers that affect the digestive tract. It makes up only about 3% of gastrointestinal cancers diagnosed in the United States each year, making it far less common than cancers of the colon, rectum, esophagus, or stomach.^[1] Because the small intestine is a long organ that folds many times inside the abdomen, it might seem surprising that cancer is so rare there. However, the exact reasons for this rarity are not fully understood by researchers.

The disease can occur in different parts of the small intestine, which consists of three sections. The first section, called the duodenum, is located near the stomach. The middle section is the jejunum, and the longest section at the end is called the ileum. Most small intestine cancers develop in either the duodenum or the ileum.^[1] The location of the tumor within these sections can influence the symptoms a person experiences and the treatment approach doctors recommend.

Different types of small intestine cancer have varying patterns of occurrence. Carcinoid tumors, which develop in hormone-producing cells, account for slightly less than half of all small intestine cancer cases. Adenocarcinomas, which start in the glandular cells lining the intestine, make up about one-third of cases.^[1] Other types include sarcomas, which begin in connective tissues, and lymphomas, which start in immune system cells.

Causes

Small intestine cancer develops when cells in the small intestine undergo changes in their DNA that cause them to grow and multiply out of control. These cells form a mass called a tumor. Over time, if the cancer continues to grow unchecked, cancer cells can break away from the original tumor and travel through the body’s lymph nodes or bloodstream to other organs, where they may form new tumors. This spreading process is called metastasis.^[1]

Researchers do not fully understand what triggers the genetic mutations that cause cells to become cancerous in the small intestine. Unlike some other cancers where specific causes have been identified, small intestine cancer does not have one clear, direct cause. Instead, scientists believe that multiple factors work together to increase the likelihood that these harmful cell changes will occur.

The disease is not contagious and cannot be transmitted from person to person like an infection. It develops spontaneously within an individual’s body when normal cellular processes go wrong. The small intestine’s role in digesting food and absorbing nutrients means its cells are constantly working and dividing to maintain the intestinal lining, and occasionally this process can result in errors that lead to cancer.

Risk Factors

Several factors can increase a person’s chances of developing small intestine cancer. Understanding these risk factors can help individuals and healthcare providers identify those who may benefit from closer monitoring, though having one or more risk factors does not guarantee that cancer will develop.^[3]

Dietary habits play a significant role in risk. People who consume a diet high in fat, particularly from red meats and processed foods, face a higher risk of developing small intestine cancer.^[3] The exact mechanism behind this association is not completely clear, but it may relate to how certain dietary components affect the intestinal lining over time or how they influence the digestive process.

Certain inherited genetic conditions substantially increase cancer risk. Familial adenomatous polyposis, or FAP, is a condition where hundreds of polyps develop in the digestive tract, and people with this syndrome have a much higher likelihood of developing small intestine cancer.^[3] Similarly, Lynch syndrome, another inherited condition, increases the risk dramatically. According to research, individuals with Lynch syndrome face approximately a 4% lifetime risk of developing small intestine cancer, which is about 100 times higher than the risk in the general population.^[26]

Inflammatory bowel diseases also increase risk. People with Crohn’s disease, a chronic inflammatory condition affecting the digestive tract, have been found to have an 8-fold increased risk of developing small intestine adenocarcinomas compared to people without this condition.^[26] The persistent inflammation appears to create an environment where cancerous changes are more likely to occur. Celiac disease, a condition where the immune system reacts to gluten, is another inflammatory condition that raises the risk.^[3]

Lifestyle factors such as smoking, alcohol consumption, and obesity may also contribute to increased risk, though their specific impact on small intestine cancer is still being studied.^[1] These factors affect overall health and may create conditions in the body that favor cancer development.

Symptoms

The symptoms of small intestine cancer can be frustratingly vague and easily confused with other, more common digestive problems. This is one reason why the cancer is often not discovered until it has progressed to a more advanced stage. The specific symptoms a person experiences often depend on where the tumor is located in the small intestine and how large it has grown.^[1]

Abdominal pain or cramping is one of the most common symptoms. This pain typically occurs in the middle of the abdomen and may feel like a general discomfort or sharp cramps. The pain might worsen after eating as food moves through the affected area of the intestine.^[2] Some people describe the sensation as persistent pressure or a dull ache that doesn’t go away.

Unexplained weight loss without trying to lose weight is another significant warning sign. When a tumor grows in the small intestine, it can interfere with the body’s ability to digest food and absorb nutrients properly. This can lead to gradual weight loss even when a person continues eating normally.^[2] The weight loss may be accompanied by feelings of weakness and fatigue.

Nausea, vomiting, and diarrhea can occur as the tumor disrupts normal digestive function. If the cancer grows large enough, it may partially or completely block the intestine, leading to more severe symptoms.^[1] A blockage can cause significant discomfort and requires immediate medical attention.

Blood in the stool is a concerning symptom that should never be ignored. The blood may appear bright red, or the stool may look dark and tarry, which indicates bleeding from higher up in the digestive tract.^[3] This bleeding can also lead to anemia, a condition where the body doesn’t have enough red blood cells to carry oxygen properly, resulting in tiredness, pale skin, and shortness of breath.^[1]

Jaundice, which causes yellowing of the skin and the whites of the eyes, can occur if a tumor in the duodenum blocks the bile duct. This prevents bile from flowing normally through the digestive system.^[1] A lump in the abdomen that can be felt during examination may also be present in some cases.^[2]

Some types of small intestine cancer, particularly carcinoid tumors, may not cause any symptoms at all. These tumors are sometimes discovered accidentally during imaging tests or procedures performed for unrelated medical issues.^[1] When carcinoid tumors do cause symptoms, they may include flushed skin, especially purplish coloring on the arms and upper body.^[1]

Prevention

Because the exact causes of small intestine cancer are not fully understood, there is no guaranteed way to prevent the disease. However, certain lifestyle choices and medical strategies may help reduce risk or detect cancer at an earlier, more treatable stage.

Dietary modifications may help lower risk. Reducing consumption of high-fat foods, particularly red meats and processed foods, is recommended based on the known association between these foods and increased cancer risk.^[3] A diet rich in fruits, vegetables, whole grains, and lean proteins supports overall digestive health and may provide protective benefits.

For people with inflammatory bowel diseases like Crohn’s disease or celiac disease, proper management of these conditions is important. Working with healthcare providers to keep inflammation under control through medication, dietary changes, and regular monitoring may help reduce cancer risk over time. People with celiac disease who strictly avoid gluten can reduce intestinal inflammation and potentially lower their risk.

Genetic counseling and testing can be valuable for individuals with a family history of inherited cancer syndromes. People diagnosed with conditions like familial adenomatous polyposis or Lynch syndrome may benefit from enhanced surveillance programs. Regular monitoring through imaging tests and endoscopic procedures can help detect any abnormal growths early when they are most treatable.

Lifestyle modifications that support overall health can also play a role. Avoiding tobacco use and limiting alcohol consumption are general cancer prevention strategies that may benefit intestinal health. Maintaining a healthy weight through regular physical activity and balanced nutrition supports the body’s ability to function properly and may reduce cancer risk.

There are currently no specific screening tests recommended for small intestine cancer in the general population, unlike colon cancer which has established screening guidelines. However, people at higher risk due to genetic conditions or inflammatory bowel disease should discuss personalized surveillance plans with their healthcare providers.

Pathophysiology

Understanding how small intestine cancer affects the body requires knowledge of the small intestine’s normal function. The small intestine is a long, tube-shaped organ that connects the stomach to the large intestine. It plays a vital role in digestion by breaking down food and absorbing nearly all the nutrients from what we eat, including vitamins, minerals, carbohydrates, fats, and proteins.^[20] The small intestine also produces hormones that aid digestion and contains immune system cells that help fight infections.

When cancer develops in the small intestine, it disrupts these normal functions in several ways. The disease begins when normal cells in the intestinal lining undergo genetic mutations that cause them to multiply uncontrollably. These abnormal cells accumulate and form a tumor. Different types of small intestine cancer originate from different cell types within the intestinal wall.

Adenocarcinomas, the most common type, start in the glandular cells that line the inside of the small intestine. These cells normally produce mucus and digestive fluids. When they become cancerous, they form tumors that typically occur in the duodenum, near the stomach. As adenocarcinomas grow, they can narrow or block the intestinal passage, preventing food from moving through normally.^[3]

Carcinoid tumors develop from neuroendocrine cells, which are specialized cells that produce hormones and help control the release of digestive juices. These tumors grow more slowly than adenocarcinomas and may not cause symptoms for a long time. Sometimes they produce excess hormones that can cause unusual symptoms like skin flushing.^[1]

Sarcomas, particularly gastrointestinal stromal tumors (GIST), originate in the connective tissues of the intestinal wall, such as muscle or cartilage. Lymphomas start in lymphocytes, which are white blood cells that are part of the immune system found throughout the intestinal tissue.^[1]

As tumors grow, they interfere with the intestine’s ability to absorb nutrients effectively. This can lead to malnutrition and weight loss even when a person is eating adequately. If a large portion of the small intestine must be removed during surgery to treat the cancer, a condition called short bowel syndrome can develop. With short bowel syndrome, there isn’t enough intestinal tissue remaining to properly absorb nutrients and water from food, leading to diarrhea, dehydration, and vitamin deficiencies.^[20]

Tumors can also cause bleeding from the intestinal wall, which may be visible in the stool or lead to anemia if the bleeding is slow but persistent. When tumors grow near the bile duct in the duodenum, they can block the flow of bile from the liver, causing jaundice and digestive problems.

If left untreated, cancer cells can break away from the primary tumor and spread through the lymphatic system or bloodstream to other organs, most commonly the liver, lungs, or lymph nodes. This process of metastasis makes the cancer much more difficult to treat and significantly impacts a person’s prognosis.