The short answer
Neuroendocrine tumors are grouped by where they start, most often the digestive tract, pancreas or lungs, and by whether they release hormones. Grade, which reflects how fast the tumor is likely to grow, is considered alongside stage and location when planning treatment.
Neuroendocrine tumors are grouped by where they start: gastrointestinal (GI) NETs, pancreatic NETs, and lung NETs are the most common groups.
Within each group, tumors are also described as functioning (hormone-releasing) or non-functioning.
Pancreatic functioning tumors have names based on the hormone they release, such as insulinoma, gastrinoma, and glucagonoma.
Grade and stage both shape treatment. For GI NETs, NCI says treatment depends mainly on whether the tumor can be removed by surgery.
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The simple version
This page explains the main types of neuroendocrine tumors (NETs) and why the grade of a tumor matters.
NETs are usually described in two ways at once. One is where they started. The other is whether they release hormones. Both matter for knowing what to expect.
Grouped by location
- Gastrointestinal (GI) NETs start in the digestive tract. The small intestine, rectum, stomach, and appendix are the usual sites. These are sometimes called carcinoid tumors.
- Pancreatic NETs start in hormone-making cells of the pancreas. They are also called islet cell tumors.
- Lung NETs start in the lungs. They are also called lung carcinoid tumors. About 9 in 10 are low-grade ("typical carcinoid") and grow slowly. The rest are intermediate-grade ("atypical carcinoid") and grow faster.
NETs can start elsewhere in the body too. Neuroendocrine cells sit in many organs.
Grouped by hormone activity
- Functioning tumors release hormones that cause symptoms. In the pancreas, each has a name based on that hormone. An insulinoma releases insulin, which lowers blood sugar. A gastrinoma releases gastrin, which causes the stomach to make too much acid. A glucagonoma releases glucagon, which raises blood sugar and can cause a skin rash. There are others.
- Non-functioning tumors do not release hormones that cause obvious symptoms. NCI notes they tend to be found at a later stage, with symptoms from the size of the tumor or its spread.
Grade and stage
Grade describes how a tumor is classified and how fast it is likely to grow. Lung NETs show the idea. The American Cancer Society says about 9 in 10 are low grade and slow growing, and the rest are intermediate grade and grow faster.
For pancreatic NETs, NCI says the stage and grade of the tumor both help guide the treatment plan, along with the type of NET and whether it makes hormones. NCI describes neuroendocrine carcinomas as the most aggressive category. For GI NETs, NCI says treatment depends mainly on whether the tumor can be removed by surgery.
Ask your care team how your tumor was graded and what that means for your plan.
Sources
- National Cancer Institute — Gastrointestinal Neuroendocrine Tumors Treatment (PDQ) – Patient Version
- National Cancer Institute — Pancreatic Neuroendocrine Tumors (Islet Cell Tumors) Treatment (PDQ) – Patient Version
- National Cancer Institute — Pancreatic NET Treatment (PDQ) – Health Professional Version
- American Cancer Society — What Is a Lung Neuroendocrine (Carcinoid) Tumor?
Common questions
Where do neuroendocrine tumors usually start?
The digestive tract, the pancreas, and the lungs are the most common sites. In the digestive tract, NCI says most occur in the small intestine, rectum, and appendix.
What is the difference between functioning and non-functioning tumors?
A functioning tumor makes hormones that cause symptoms. A non-functioning tumor does not, so NCI notes it tends to be found at a later stage, with symptoms from the size of the tumor or its spread.
What are examples of pancreatic neuroendocrine tumors?
Pancreatic NETs that release hormones are named for that hormone: insulinoma (insulin, causing low blood sugar), gastrinoma (gastrin, causing extra stomach acid), and glucagonoma (glucagon, causing high blood sugar and a skin rash), among others.
What does grade mean for a NET?
Grade is part of how a tumor is classified. For lung NETs, the American Cancer Society says about 9 in 10 are low grade and slow growing, and the rest are intermediate grade and grow faster. Ask your care team how your tumor was graded.
Does grade matter more than stage for NETs?
NCI says both the stage and the grade of a pancreatic NET help guide treatment. For GI NETs, NCI says treatment depends mainly on whether the tumor can be removed by surgery. Ask your care team how grade and stage apply to you.
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Last updated: 2026-10-02Next planned review: 2027-08-03
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Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes, and this is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and then compared with the sources listed on it, looking for statements those sources do not back up. That check is not a sentence-by-sentence record and can miss errors. It is not a medical review, and it does not confirm the page is complete or right for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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