Gastrointestinal neuroendocrine tumors are rare cancers that develop in specialized cells of the digestive system, often growing slowly and sometimes without symptoms for years. Treatment approaches range from careful monitoring to surgery and specialized therapies, depending on tumor location, size, and stage—offering many patients the possibility of long-term control or even cure.

Understanding Treatment Goals for Gastrointestinal Neuroendocrine Tumors

When someone receives a diagnosis of a gastrointestinal neuroendocrine tumor, the first question that often comes to mind is: what happens next? The answer depends on many factors unique to each person. Treatment for these tumors focuses on several goals: controlling symptoms that can significantly affect daily life, slowing or stopping tumor growth, preventing the cancer from spreading to other parts of the body, and improving overall quality of life.^[1]

The approach to treating gastrointestinal neuroendocrine tumors is highly personalized. Doctors consider where the tumor is located in the digestive tract—whether it’s in the stomach, small intestine, appendix, colon, or rectum. They also look at the tumor’s size, how fast it’s growing, whether it has spread to lymph nodes or other organs like the liver, and whether it’s producing excess hormones that cause symptoms.^[4] Some tumors are discovered accidentally during tests for other conditions and may be so small and slow-growing that immediate treatment isn’t necessary. Others require prompt intervention.

Medical societies and organizations have established standard treatments based on years of research and clinical experience. These proven approaches form the backbone of care for gastrointestinal neuroendocrine tumors.^[1] At the same time, researchers continue to study new therapies in clinical trials, testing innovative drugs and treatment methods that may offer additional options for patients, particularly those whose tumors don’t respond well to standard treatments or who have advanced disease.^[1]

The treatment journey often involves a team of specialists working together. This team might include surgeons who can remove tumors, medical oncologists who manage drug therapies, gastroenterologists who perform diagnostic procedures, radiologists who interpret imaging tests, and specialized nurses who coordinate care and provide education and support.^[4] Each member brings expertise that contributes to developing the best treatment plan for each individual patient.

Standard Treatment Approaches

Surgery as the Primary Treatment

For many people with gastrointestinal neuroendocrine tumors, surgery represents the most effective treatment and the best chance for cure. When a tumor is localized—meaning it hasn’t spread beyond its original site—surgical removal can completely eliminate the cancer.^[1] The type of surgery depends on where the tumor is located and how large it has grown.

In the stomach, small tumors may be removed through an endoscopy, a procedure where a flexible tube with a camera is passed down the throat, allowing the doctor to see and remove the tumor without making any incisions in the abdomen. Larger stomach tumors might require removing part of the stomach through traditional surgery.^[1] For tumors in the small intestine, surgeons typically remove the affected section of bowel along with nearby lymph nodes to check for cancer spread. Appendix tumors often come out during an appendectomy, and if the tumor is small and confined to the appendix, no further treatment may be needed.^[1]

Rectal tumors are often removed using techniques that preserve bowel function. Small rectal neuroendocrine tumors can sometimes be taken out through the anus without external incisions. Larger ones may require more extensive surgery.^[1] Even when the cancer has spread to the liver, surgery may still be an option. Doctors can sometimes remove portions of the liver containing metastatic tumors, which can significantly extend survival and improve quality of life.^[1]

Hormone Therapies

Many gastrointestinal neuroendocrine tumors produce hormones, and some treatment approaches work by targeting this hormone production. Somatostatin analogues are medications that mimic a natural hormone called somatostatin, which normally helps regulate other hormones in the body. The two main somatostatin analogues used are octreotide and lanreotide.^[4]

These medications serve dual purposes. First, they help control symptoms caused by excess hormone production, particularly those of carcinoid syndrome—a condition that can cause flushing of the skin, diarrhea, wheezing, and rapid heartbeat. Second, somatostatin analogues can slow tumor growth in some patients, helping to keep the cancer stable for months or years.^[4] Patients typically receive these medications as injections, either monthly or every few weeks, depending on the specific drug and formulation used.

Common side effects of somatostatin analogues include digestive problems like nausea, diarrhea or constipation, and abdominal pain. Some people develop gallstones because these medications affect gallbladder function. Pain or irritation at the injection site is also common. Most side effects are manageable and tend to decrease over time as the body adjusts to the medication.^[4]

Liver-Directed Therapies

Because gastrointestinal neuroendocrine tumors frequently spread to the liver, specialized treatments targeting liver metastases have become important tools. These interventional radiology procedures work by either blocking blood flow to tumors or delivering treatment directly to cancer cells in the liver.^[4]

One approach is hepatic artery embolization, which involves blocking the arteries that supply blood to liver tumors. Since tumors depend heavily on blood supply for nutrients and oxygen, cutting off this supply can cause them to shrink. A variation called chemoembolization combines blocking the blood vessels with injecting chemotherapy drugs directly into the liver, delivering high doses of medication to the tumor while minimizing exposure to the rest of the body.^[4]

Radiofrequency ablation uses heat generated by radio waves to destroy tumor tissue. A thin needle is inserted into the tumor, usually guided by ultrasound or CT imaging, and heat is applied to kill cancer cells. This works best for smaller tumors. Another technique called cryoablation uses extreme cold instead of heat to destroy tumors.^[4]

These liver-directed treatments can cause temporary side effects including fever, nausea, abdominal pain, and fatigue lasting several days to a few weeks after the procedure. More serious complications are rare but can include bleeding, infection, or damage to nearby organs.^[4]

Chemotherapy

Chemotherapy uses drugs that kill rapidly dividing cancer cells throughout the body. For gastrointestinal neuroendocrine tumors, chemotherapy is typically reserved for more aggressive, faster-growing tumors or when the cancer has spread extensively and other treatments haven’t worked.^[4]

Well-differentiated neuroendocrine tumors, which are the slower-growing type, often don’t respond well to traditional chemotherapy. However, poorly differentiated tumors and neuroendocrine carcinomas—which grow more aggressively—may be treated with chemotherapy combinations similar to those used for small cell lung cancer. Common regimens include drugs like etoposide combined with cisplatin or carboplatin.^[3]

For certain types of pancreatic and gastrointestinal neuroendocrine tumors, doctors may use a combination called CAPTEM, which includes capecitabine and temozolomide. Another option is streptozocin combined with fluorouracil.^[4] The specific chemotherapy regimen, treatment schedule, and duration depend on tumor characteristics and how well the patient tolerates the medication.

Chemotherapy side effects vary depending on which drugs are used but commonly include fatigue, nausea and vomiting, hair loss, increased risk of infections due to low white blood cell counts, and mouth sores. Many of these side effects can be managed with supportive medications, and most resolve after treatment ends.^[4]

Radiation Therapy

External beam radiation therapy, which directs high-energy rays at cancer cells to destroy them, is used less commonly for gastrointestinal neuroendocrine tumors than for many other cancers. However, it can be helpful in specific situations, such as treating tumors that have spread to bones and are causing pain, or targeting cancer in areas where surgery isn’t possible.^[4]

A specialized form called peptide receptor radionuclide therapy (PRRT) has become an important treatment option in recent years. This approach takes advantage of the fact that many neuroendocrine tumor cells have receptors for somatostatin on their surface. A radioactive substance is attached to a molecule similar to somatostatin, and when injected into the bloodstream, it seeks out and binds to tumor cells throughout the body, delivering radiation directly to the cancer. Lutetium Lu 177 dotatate is one such treatment approved for use in certain gastrointestinal neuroendocrine tumors.^[4]

PRRT is typically given as an infusion through a vein, with treatments repeated several times over a period of months. Side effects can include nausea, vomiting, and effects on kidney function and bone marrow, which require monitoring through regular blood tests. This therapy can help shrink tumors, slow their growth, and improve symptoms in many patients.^[4]

Treatment Being Tested in Clinical Trials

While standard treatments work well for many patients with gastrointestinal neuroendocrine tumors, researchers are continuously working to develop new and more effective therapies. Clinical trials test these innovative approaches to determine whether they are safe and work better than existing treatments.

Targeted Therapy

Targeted therapies are drugs designed to attack specific molecular features of cancer cells while causing less harm to normal cells. Unlike traditional chemotherapy, which affects all rapidly dividing cells, targeted drugs zero in on particular proteins or pathways that cancer cells use to grow and survive.^[4]

One class of targeted drugs being studied for neuroendocrine tumors includes mTOR inhibitors. The mTOR protein is part of a signaling pathway that helps control cell growth and division. When this pathway becomes overactive in cancer cells, it drives tumor growth. Drugs like everolimus work by blocking mTOR, essentially putting the brakes on cancer cell growth. Everolimus has been approved for pancreatic neuroendocrine tumors and is being studied in gastrointestinal neuroendocrine tumors in various clinical trials.^[4]

Another group of targeted therapies focuses on blood vessel formation. Tumors need blood vessels to supply nutrients and oxygen as they grow, a process called angiogenesis. Drugs called angiogenesis inhibitors block the signals that tumors send to create new blood vessels. By cutting off the tumor’s blood supply, these drugs can slow or stop growth. Drugs like sunitinib and bevacizumab work through this mechanism and are being evaluated in clinical trials for gastrointestinal neuroendocrine tumors.^[4]

These targeted therapies are typically tested in Phase II and Phase III clinical trials. Phase II trials focus on determining whether the drug works against the specific cancer—in this case, whether it can shrink tumors or slow their growth in patients with gastrointestinal neuroendocrine tumors. Phase III trials compare the new drug to standard treatment to see if it offers better outcomes.^[4] Patients in these trials are carefully monitored for both effectiveness and side effects.

Common side effects of targeted therapies differ from traditional chemotherapy. mTOR inhibitors can cause mouth sores, skin rashes, increased blood sugar, increased cholesterol levels, and fatigue. Angiogenesis inhibitors may cause high blood pressure, fatigue, decreased appetite, and changes in blood counts. While these side effects can be significant, they are often manageable with dose adjustments or supportive medications.^[4]

Immunotherapy

Immunotherapy represents one of the most exciting areas of cancer research. These treatments work by helping a person’s own immune system recognize and attack cancer cells. While the immune system normally identifies and destroys abnormal cells, cancer cells have developed ways to hide from or suppress immune responses. Immunotherapy aims to overcome these evasion tactics.^[4]

One approach involves drugs called checkpoint inhibitors. Cancer cells often exploit molecular “checkpoints” that normally prevent the immune system from attacking the body’s own cells. By blocking these checkpoints, drugs like pembrolizumab and nivolumab can unleash the immune system to fight cancer. These drugs are being tested in clinical trials for patients with advanced or high-grade neuroendocrine tumors that haven’t responded to other treatments.^[4]

Immunotherapy tends to work best in tumors with certain characteristics, such as high levels of genetic mutations or specific biomarkers. Researchers are working to identify which patients with gastrointestinal neuroendocrine tumors are most likely to benefit from these treatments. Clinical trials are exploring immunotherapy both alone and in combination with other treatments like targeted therapy or chemotherapy.

The side effects of immunotherapy are different from those of chemotherapy because they result from an overactive immune response rather than direct toxicity to cells. These can include fatigue, skin rash, diarrhea, and inflammation of various organs including the lungs, liver, intestines, or hormone-producing glands. While most side effects are mild to moderate, some can be serious and require treatment with steroids or other immune-suppressing drugs.^[4]

Novel Radionuclide Therapies

Building on the success of lutetium Lu 177 dotatate, researchers are developing new radioactive compounds that can target neuroendocrine tumor cells even more effectively. These experimental treatments attach different radioactive isotopes to molecules that bind to receptors on tumor cells, allowing radiation to be delivered directly to cancer throughout the body.^[4]

Some clinical trials are testing higher doses of existing radionuclide therapies or multiple cycles of treatment to see if this improves outcomes. Others are combining radionuclide therapy with other treatments like chemotherapy or targeted drugs to achieve better tumor control. Phase I and Phase II trials evaluate the safety, optimal dosing, and effectiveness of these novel approaches.

Combination Approaches

Recognizing that cancer is complex and uses multiple pathways to grow and survive, many clinical trials now test combinations of different types of treatments. Researchers are exploring whether combining targeted therapy with immunotherapy, or adding chemotherapy to radionuclide therapy, might produce better results than any single treatment alone.^[4]

These combination studies typically start in Phase I trials, where the main goal is to determine safe doses of the drugs when used together and to identify any unexpected interactions or side effects. If the combination appears safe and shows promising signs of activity against the cancer, it moves to Phase II trials to better understand its effectiveness. Successful Phase II results can lead to Phase III trials, which directly compare the new combination to the current standard of care.

Early results from some combination trials have shown encouraging signs, with some patients experiencing tumor shrinkage or longer periods without cancer progression. However, it’s important to remember that these are preliminary findings, and more research is needed to confirm whether combination approaches truly improve outcomes and are worth any additional side effects they might cause.

Most Common Treatment Methods

• Surgery
  • Endoscopic removal for small stomach and rectal tumors without external incisions
  • Surgical resection of affected bowel sections for small intestine tumors
  • Appendectomy for appendiceal tumors
  • Liver resection for metastases confined to portions of the liver
  • Complete tumor removal offers the best chance for cure when cancer is localized
• Hormone therapy (Somatostatin analogues)
  • Octreotide and lanreotide delivered as regular injections
  • Control symptoms of carcinoid syndrome including flushing and diarrhea
  • Slow tumor growth and help maintain disease stability
  • Treatment often continues long-term, with injections every few weeks
• Liver-directed therapies
  • Hepatic artery embolization to block blood supply to liver tumors
  • Chemoembolization combining vessel blocking with localized chemotherapy
  • Radiofrequency ablation using heat to destroy tumor tissue
  • Cryoablation using extreme cold to kill cancer cells
  • Particularly useful when tumors have spread to the liver
• Chemotherapy
  • Etoposide combined with cisplatin or carboplatin for aggressive tumors
  • CAPTEM regimen (capecitabine and temozolomide) for certain tumor types
  • Streptozocin-based combinations for selected cases
  • More effective for poorly differentiated, fast-growing tumors
• Peptide receptor radionuclide therapy (PRRT)
  • Lutetium Lu 177 dotatate delivers radiation directly to tumor cells
  • Targets somatostatin receptors present on many neuroendocrine tumors
  • Given as intravenous infusions repeated over several months
  • Can shrink tumors and improve symptoms
• Targeted therapy
  • mTOR inhibitors like everolimus block cell growth pathways
  • Angiogenesis inhibitors such as sunitinib and bevacizumab prevent new blood vessel formation
  • Designed to attack specific molecular features of cancer cells
  • Being studied in clinical trials for gastrointestinal neuroendocrine tumors
• Immunotherapy
  • Checkpoint inhibitors like pembrolizumab and nivolumab activate the immune system
  • Help immune cells recognize and attack cancer
  • Tested in clinical trials for advanced or high-grade tumors
  • May work better in tumors with specific characteristics
• Watchful waiting
  • Careful monitoring with regular imaging and blood tests
  • Appropriate for very small, slow-growing tumors without symptoms
  • Treatment begins only if tumor shows growth or causes problems
  • Helps avoid unnecessary treatment and side effects