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What is neuroendocrine tumors (nets)?
Neuroendocrine tumors, or NETs, grow from neuroendocrine cells — specialized cells scattered throughout the body that act like a bridge between the nervous system and the hormone (endocrine) system. These cells release hormones that help control body functions, and they're found in many places, especially the digestive tract and the lungs. NETs are a diverse family: some are tiny and slow-growing and may never cause trouble, while others grow faster and behave more like typical cancers. A key feature is that some NETs make extra hormones that cause specific symptoms — for example flushing, diarrhea, or wheezing in a condition called carcinoid syndrome — while others, called non-functional, cause no hormone symptoms at all. Because many NETs grow slowly and carry special targets on their surface, they have unique treatment options, including a remarkable form of targeted radiation that travels through the bloodstream to find tumor cells anywhere in the body.
The main types
Doctors group neuroendocrine tumors (nets) by where it starts and how it behaves:
| Type | What it means, simply |
|---|---|
| Gastrointestinal NETs (carcinoid) | The most common type, starting in the stomach, small intestine, appendix, or rectum; often slow-growing and sometimes hormone-producing. |
| Pancreatic NETs | NETs of the pancreas, which can make hormones like insulin or gastrin that cause specific symptoms, or be non-functional. |
| Lung (bronchial) NETs | Neuroendocrine tumors in the lungs, ranging from slow-growing typical carcinoids to more active forms. |
| Grade (how fast cells divide) | NETs are graded G1, G2, or G3 by how quickly the cells multiply; well-differentiated low-grade tumors behave gently, while high-grade neuroendocrine carcinomas are aggressive and treated differently. |
Staging, in plain terms
NETs use a TNM stage like other cancers, but grade matters just as much. Grade describes how fast the tumor cells are dividing — measured by a marker called Ki-67 — and sorts tumors into low (G1), intermediate (G2), or high (G3) grade. A small, low-grade NET behaves very differently from a high-grade one, so doctors always consider stage and grade together when planning treatment.
| AJCC TNM plus tumor grade (Ki-67 / mitotic rate) | What it generally means |
|---|---|
| Localized (Stage I-II) | The tumor is confined to where it started; surgery often cures it, especially for small, low-grade tumors. |
| Regional (Stage III) | Spread to nearby lymph nodes or tissues; treatment combines surgery with other therapies depending on grade. |
| Metastatic (Stage IV) | Spread to distant organs, most often the liver; even so, low-grade NETs can be controlled for many years with a range of treatments. |
| Grade overlay (G1-G3) | Independent of stage, grade guides therapy — low-grade tumors are watched or treated gently, while high-grade carcinomas need prompt, intensive treatment. |
The standard of care
Neuroendocrine Tumors (NETs) is almost always treated by a team that may include a surgeon, a medical oncologist, and a radiation oncologist, combining therapies for the best result. The usual building blocks are:
Surgery
Removing the tumor is the main path to cure for localized NETs, and even reducing tumor bulk can ease hormone symptoms and improve quality of life in advanced disease.
Somatostatin analogs
Injections such as octreotide or lanreotide both calm hormone-related symptoms and slow the growth of many low-grade NETs, often for years.
Peptide receptor radionuclide therapy (PRRT)
A targeted radiation treatment given through the bloodstream that homes in on NET cells anywhere in the body and delivers radiation directly to them.
Other systemic & local therapies
Targeted pills, chemotherapy (especially for high-grade tumors), and liver-directed treatments help control disease that has spread.
How radiation treatment works
Radiation treats neuroendocrine tumors in two complementary ways. The first, external-beam radiation, uses focused high-energy x-rays from a machine to damage the DNA of tumor cells in a defined area so they stop growing — useful for a tumor that can't be removed or a painful deposit. The second is special to NETs: peptide receptor radionuclide therapy, or PRRT. Because most neuroendocrine cells carry a particular receptor on their surface, doctors can attach a radioactive atom to a molecule that seeks out that receptor, infuse it into the bloodstream, and let it travel through the body to deliver radiation directly to tumor cells wherever they hide — even tiny deposits scattered in the liver or bones. This 'theranostic' approach means the same targeting can be used first to image the tumors and then to treat them. Treatments are generally well tolerated; PRRT is given as a series of infusions, and side effects such as temporary fatigue or mild nausea are usually manageable.
The main ways radiation is delivered for neuroendocrine tumors (nets):
Peptide receptor radionuclide therapy (PRRT)
A radioactive atom is attached to a molecule that locks onto receptors found on most NET cells. Given by infusion, it circulates through the body, sticks to tumor cells wherever they are, and delivers radiation precisely to them while largely sparing healthy tissue.
External-beam radiation
Focused radiation from outside the body can treat a NET that can't be removed or relieve symptoms from a specific deposit, such as one pressing on bone or causing pain.
Stereotactic radiation (SBRT)
Very precise, high-dose radiation in a few sessions can control a limited number of spots — for example in bone or the liver — while protecting nearby organs.
Latest studies shaping care
Care keeps improving — often toward getting the same excellent results with less burden on patients. A few developments:
PRRT improves outcomes: The NETTER-1 trial showed that targeted radionuclide therapy markedly delayed tumor growth and improved quality of life for advanced midgut NETs, establishing PRRT as a standard option.[1]
NETTER-1 trial, NEJM
PRRT moving earlier in treatment: The NETTER-2 trial found benefit from using PRRT earlier, in higher-grade well-differentiated tumors, expanding who may benefit from this therapy.[2]
NETTER-2 trial, Lancet
Somatostatin analogs slow growth: Long-acting octreotide and lanreotide were shown to slow tumor progression in low-grade NETs, not just control hormone symptoms, making them a cornerstone of care.[3]
PROMID and CLARINET trials
Common questions
Are all neuroendocrine tumors cancer? Most NETs are considered cancers, but many — especially low-grade ones — grow so slowly that they behave more like a chronic condition than an aggressive cancer. Some tiny NETs found by chance may never cause problems. The grade and stage together tell your team how concerned to be and how actively to treat.
What is PRRT, in simple terms? PRRT is a targeted radiation treatment given through a vein. A radioactive particle is attached to a molecule that latches onto neuroendocrine tumor cells, so the radiation is carried straight to the tumors throughout the body and delivered from the inside, sparing most healthy tissue. It's a powerful option for NETs that have spread.
Can neuroendocrine tumors be cured? Localized NETs are often cured by surgery. When they've spread, many — particularly low-grade tumors — can still be controlled for many years with somatostatin injections, PRRT, and other therapies, allowing people to live well for a long time.
References
Numbered sources for the studies cited above. Links open the primary publication on PubMed or the publisher’s site.