Neuroendocrine Tumors (NETs) is a “catch-all” category for a group of solid tumors that arise from neuroendocrine cells, which are cells that release hormones in response to a signal from the central nervous system.

NETs occur most often in the gastrointestinal (GI) tract, but, as neuroendocrine cells are found in virtually every organ of the body, they may also occur in the lungs, kidneys, etc.

The two most common NETs are Carcinoid and Pancreatic Islet Cell tumors.  Carcinoids occur in the GI tract, and are classified as foregut, midgut or hindgut depending on location.  Islet cell tumors occur in the pancreas and make up 5% of all pancreatic cancers.  (It is important to note that pancreatic islet cell is completely different than the more common pancreatic adenocarcinoma, which is NOT a neuroendocrine tumor.)

Other, less common tumors within the NETs umbrella include:

Paragangliomas, Pheochromocytomas, and Merkel cell carcinoma.

The majority of NETs are indolent (slow growing), low-grade tumors that are well-differentiated.  However, while much less common, there are NETs  which are faster growing (high grade) tumors which can be highly aggressive.  It is important to distinguish between the two as therapeutic interventions vary greatly between the two.

Is it cancer?  YES.  It can, and most often does spread, unless caught very early.  The most common sites for disease spread (metastases) are the lymph nodes, liver, mesentery and bones.  Confusing to patients, this disease can be referred to by many different names; it can be known as neuroendocrine tumor (NET), neuroendocrine cancer, carcinoid cancer, pancreatic islet cell NET,  or cancer, carcinoid cancer of the lungs, etc.  Regardless of primary site, once the cancer has spread, the same set of potential interventions apply.

Occasionally, a medical professional will refer to a tumor as “benign” if it has not spread and has been resected (surgically removed).  All neuroendocrine tumors have the potential to spread, whether they have at diagnosis or not.  Patients should be aware of this, and aware that some reasonable frequency of monitoring (often or not often, as each situation dictates) for up to 10 years may be appropriate.  Having said that, it is true that some tumor primary sites are less likely to spread to distant sites than others.

If you are not confused enough already, NETs are also divided into two categories:  functional or non-functional.

“Functional tumors” refers to those tumors which secrete hormones (above and beyond normal body function) and cause different syndromes, each classified by an array of symptoms.  Carcinoid syndrome, primarily caused by excess serotonin, is the most prevalent syndrome associated with these tumors.  Pancreatic islet cell tumors are most often non-functional, but in some cases can cause additional syndromes, depending on their secreted hormone.

Carcinoid syndrome can be comprised of any combination, or all of the following:  diarrhea, flushing, wheezing, swelling, shortness of breath, abdominal pain, fatigue, heart disease, bloating and heart palpitations.


There are some excellent foundations serving patients with this disease which do an extraordinary job of detailing information and resources for patients.    On their sites, you can find lists of qualified medical specialists, as well as, local support groups.

For much more detailed information, please see our patient resources link for foundations which serve the net patient community.