Back to
Updated on March 18, 2025
Neuroendocrine tumors (NETs) are a rare type of cancer that originate in neuroendocrine cells, a type of cell that produces and releases hormones in response to signals from the nervous system. The hormones released by neuroendocrine cells control many essential functions throughout the body, including mood, metabolism, sleep, temperature, and many others.
NETs begin when normal neuroendocrine cells undergo mutations and begin to grow in an abnormal, uncontrolled way.
There are different types of neuroendocrine cells, which are located in different tissues and organs throughout the body. Likewise, there are different types of NETs that can occur in various locations throughout the body.
One way of categorizing NETs is whether the cancer began in the pancreas (pancreatic NETs) or a place outside the pancreas (extra-pancreatic NETs).
Pancreatic NETs and extra-pancreatic NETS
The pancreas is an organ located in the upper abdomen, behind the stomach. This organ produces and releases enzymes that the body needs to digest food. It also releases hormones that balance the amount of glucose in the blood (glucose is a blood sugar that is the body’s main source of energy).
Numbers vary depending on the source, but less than 10 percent of NETs are pancreatic NETs. The majority of extra-pancreatic NETs (up to 90 percent according to some sources) occur in the gastrointestinal tract (GI tract). Extra-pancreatic NETs also occur in the lungs, urinary tract, and other locations throughout the body.
Why pancreatic vs. extra-pancreatic?
Different parts of the body contain different types of neuroendocrine cells. The neuroendocrine cells where a NET originates will influence how that cancer grows and behaves.
NETs that occur in the pancreas tend to behave differently than extra-pancreatic NETs that occur in other locations in the body (and again, in most cases, “extra-pancreatic” refers to NETs that begin in the GI tract). Pancreatic NETs and extra-pancreatic NETs can cause different symptoms and require different approaches to treatment.
Both pancreatic and extra-pancreatic NETs can be categorized as functional or non-functional depending on whether the cancer cells are producing hormones.
What are functional NETs?
“Functional” refers to whether the cancerous cells are producing hormones. Because NET cells originate from hormone-producing neuroendocrine cells, some NETs retain this hormone-producing functionality after cells have become cancerous.
These cancers produce excess hormones that can cause a variety of symptoms, which are sometimes referred to as hormonal symptoms. Hormonal symptoms can vary depending on the type of hormones that are being produced by the NET. Common hormonal symptoms include:
- Flushing skin
- Diarrhea and/or fatty stools
- Frequent urination
- High or low blood glucose (blood sugar)
- Gastric ulcers
- Dizziness
- Shakiness
- Heart palpitations
- Mouth sores
- Anxiety, confusion, difficulty thinking
What are non-functional NETs?
“Non-functional” means that the cancer cells are not producing hormones or not producing enough hormones to cause symptoms.
Non-functional NETs typically cause mechanical symptoms, or symptoms caused by the presence of a tumor in a specific location of the body. For example, if a pancreatic tumor is pushing against a nerve and causing pain, or a GI tumor is blocking a section of the bowel. In many cases, non-functional NETs do not cause any symptoms until the cancer has advanced and are not diagnosed until it has reached an advanced stage.
It’s important to remember that there are different types of NETs, and symptoms can overlap. In addition to causing hormonal symptoms, functional NETs can also cause mechanical symptoms. NETs can also cause symptoms that overlap with other types of cancers. These include fatigue, weight loss, and symptoms related to the location of the tumor—for example, NETs in the lungs can cause symptoms that occur with other types of lung cancer.
Treatment for NETs
Surgery to remove the cancer (or as much of the cancer as possible) is often the first choice of treatment for functional and non-functional NETs. Treatment also often includes medications called somatostatin analogs (SSAs). These medications can reduce the amount of hormones being made and help alleviate symptoms caused by excess hormones in functional NETs. These medications can also slow the growth and reduce the size of some non-functional NETs.
Treatment can also include radiation, chemotherapy, and or targeted therapy drugs (drugs that acts on specific substances that cancer cells need to survive).
Treatment for an NET will be different for everyone. Your best source of information will be a healthcare team experienced in treating this rare type of cancer.
