Neuroendocrine Tumors (NETs): What to Know on World NET Cancer Day

November 10, 2026 · Cancer Information

A smiling doctor in a white coat talks with a patient in a clinic. — Photo: National Cancer Institute on Unsplash

Today, November 10, is World NET Cancer Day. Neuroendocrine tumors, or NETs, are uncommon cancers that are often slow-growing and easy to miss, and they can take years to diagnose because their symptoms look like everyday problems. Here's what to know.

What neuroendocrine tumors are

Neuroendocrine cells are found throughout the body. They're a bit like nerve cells and a bit like hormone-making cells, and they help control things such as digestion and breathing. Tumors that start in these cells are called neuroendocrine tumors. Some make extra hormones, which can cause symptoms of their own.

You may also hear the older name carcinoid tumor, which is still often used for NETs of the digestive tract and lungs.

Where NETs start

The digestive tract. Gastrointestinal NETs most often start in the small intestine, rectum and appendix, and sometimes in the stomach or colon. The American Cancer Society estimates about 8,000 are diagnosed in the U.S. each year, and the number has been rising for many years, possibly because more are found by chance on tests done for other reasons. The average age at diagnosis is in the early 60s.
The pancreas. Pancreatic NETs, also called islet cell tumors, make up less than 2% of pancreatic cancers. They're a different disease from the more common pancreatic cancer (adenocarcinoma), with different tests and treatments, and they generally have a better outlook.
The lungs. About 1% to 2% of lung cancers are NETs. Most are "typical" carcinoids, which grow slowly, rarely spread beyond the lungs, and don't seem to be linked to smoking.

Symptoms

Many NETs cause no symptoms for a long time and are found by accident. For example, NETs of the appendix are often found when the appendix is removed for another reason. When digestive NETs do cause symptoms, these can include cramps or belly pain, bloating, diarrhea, nausea, weight loss and tiredness. These symptoms may come and go for years, which is one reason NETs are easily mistaken for conditions such as irritable bowel syndrome. Rectal NETs may cause bleeding, pain or constipation.

Carcinoid syndrome

About 1 in 10 carcinoid tumors release enough hormone-like substances to cause a group of symptoms called carcinoid syndrome:

flushing (redness and warmth) of the face and neck
severe diarrhea
wheezing or trouble breathing
a fast heartbeat

Stress, heavy exercise and alcohol can trigger these symptoms. Most cases happen after the tumor has spread, especially to the liver. Over time, the substances can damage heart valves, so people with carcinoid syndrome need their heart checked.

How NETs are found

Doctors may use:

Blood tests for hormones, including a tumor marker called chromogranin A;
a 24-hour urine test for 5-HIAA, a breakdown product of serotonin, to help diagnose carcinoid syndrome;
imaging such as CT, MRI and special nuclear medicine scans;
endoscopy, colonoscopy or capsule endoscopy to look inside the digestive tract, and a biopsy to confirm the diagnosis.

How NETs are treated

Treatment depends on where the tumor is, its grade (how fast it's likely to grow) and whether it has spread:

Surgery to remove the tumor, which can be curative for many tumors found early. Some small rectal and stomach tumors can be removed during an endoscopy.
Somatostatin analogs, such as octreotide and lanreotide. These hormone-blocking drugs help control flushing and diarrhea and may also slow tumor growth.
Peptide receptor radionuclide therapy (PRRT). In 2018, the FDA approved lutetium Lu 177 dotatate (Lutathera), a radioactive drug that seeks out tumors carrying somatostatin receptors, for adults with these tumors in the digestive tract and pancreas. It was the first drug of its kind approved for these cancers.
Liver-directed treatments, such as blocking the blood supply to tumors in the liver, plus chemotherapy, radiation and other drugs in some cases.

Because NETs are uncommon, it can help to be seen at a center with a team experienced in treating them. Our directory lists cancer research centers and oncologists, and you can read more about gastrointestinal carcinoid tumors.

The bottom line

NETs are uncommon and often slow-growing, but they're easy to miss. If you have long-running belly symptoms, diarrhea or flushing that haven't been explained, ask your doctor whether a neuroendocrine tumor could be the cause. And if you've been diagnosed, look for a care team with NET experience.

This article is for general information and is not medical advice. Talk with your doctor about your own situation.