Updated on April 10, 2025.
Neuroendocrine tumors (NETs) are a rare type of cancer that originate in neuroendocrine cells. Found in many locations throughout the body, neuroendocrine cells produce and release hormones in response to signals from the nervous system. These hormones control many essential functions throughout the body, including mood, metabolism, sleep, and temperature regulation (among many others).
NETs begin when normal neuroendocrine cells undergo mutations and begin to grow in an abnormal, uncontrolled way. Gastroenteropancreatic neuroendocrine tumors (GEP-NETS) refer to NETs that occur in the gastrointestinal tract or the pancreas.
Here are four things to know.
GEP-NETs can be grouped into pancreatic and extrapancreatic
GEP-NETs can be divided into pancreatic NETs and extrapancreatic NETs.
Pancreatic NETs begin in the pancreas, a large gland located behind the stomach. This gland produces and releases enzymes needed for digestion and hormones needed to balance the amount of glucose (blood sugar) in the blood.
Extrapancreatic NETs occur in parts of the body outside the pancreas—the gastrointestinal tract, the lungs, urinary tract, or other parts of the body where neuroendocrine cells are located.
Only a small percentage of NETs are pancreatic NETs, but NETs that occur in the pancreas tend to behave differently than NETs that occur in other locations in the body.
Most GEP-NETs are gastrointestinal (GI) NETs
In general, NETs are considered rare. While the exact prevalence is not known, healthcare researchers estimate that NETs affect between 4 and 6 out of every 100,000 people.
Gastrointestinal neuroendocrine tumors (GI-NETs) are the most common. Gastrointestinal neuroendocrine tumors (GI-NETs) are NETs that begin in the digestive tract, with the majority occurring in the appendix, small intestine, and rectum.
While exact statistics are not known, up to 90 percent of extra-pancreatic NETs occur in the gastrointestinal tract. The remaining 10 percent occur in the pancreas, the lungs, or other locations throughout the body.
GEP-NETs can be functional or non-functional
GEP-NETs originate from hormone-producing neuroendocrine cells, and some GEP-NETs retain this hormone-producing functionality after cells have become cancerous.
GEP-NETs that produce hormones are called functional GEP-NETs and cause what are called functional symptoms, symptoms related to hormone imbalances. Functional symptoms can include flushing skin, diarrhea and/or fatty stools, frequent urination, changes in blood glucose levels, gastric ulcers, dizziness, shakiness, heart palpitations, mouth sores, anxiety, confusion, and difficulty thinking.
Non-functional GEP-NETs do not produce hormones (or do not produce enough hormones to cause symptoms). Non-functional NETs tend to cause mechanical symptoms, symptoms caused by a tumor pressing against tissues, nerves, organs, or other structures in the body. Examples of mechanical symptoms include abdominal pain, nausea, vomiting, constipation, and bleeding.
GEP-NETs can also cause symptoms that overlap with other types of cancers, including fatigue and unexplained weight loss.
Surgery is the preferred treatment option
While treatment for a GEP-NET is different for everyone—and a healthcare provider will be your best source of information about treatment options—surgery is usually the first choice for treatment. The goal of surgery is to remove the tumor (or as much of the tumor as possible).
Medications called somatostatin analogs (SSAs) are also frequently a part of treatment. These medications can ease functional symptoms (if a GEP-NET is functional) as well as slow the growth and reduce the size of tumors (including non-functional GEP-NETs).
Targeted therapy and peptide receptor radionuclide therapy (PRRT) are other treatment options. Targeted therapies are anti-cancer drugs that work by targeting specific features found on cancer cells. Many work by blocking proteins that cancer cells need to grow and spread. PRRT is a drug that works by attaching to cancer cells and delivering radioactive substances that destroy those cancer cells.
Chemotherapy may also be used, especially in cases where a GEP-NET is aggressive and likely to grow and spread quickly.
