Neuroendocrine Tumours (NETs): Symptoms, Causes, Stages, Diagnosis and Treatment 

Introduction

Persistent digestive problems, unexplained abdominal discomfort or pain, changes in bowel habits, flushing, weight changes, or ongoing tiredness can leave you wondering what might be causing them. In some cases, these symptoms may be linked to neuroendocrine tumours (NETs), which can develop in different parts of the body¹. This article covers everything you need to know about NET, including its causes, symptoms, types, risk factors, diagnosis, treatment options, and when to seek medical attention. 

What Is a Neuroendocrine Tumour (NET)?

A neuroendocrine tumour (NET) is an abnormal growth that develops from neuroendocrine cells². Neuroendocrine cells have features of both nerve cells and hormone-producing cells and they release hormones in response to signals from the nervous system³. NETs have variable malignant potential and can occur in different parts of the body such as the stomach, intestine, lungs, and pancreas³. Some NETs produce excess hormones and can cause different symptoms².

Types of Neuroendocrine Tumours

There are different types of neuroendocrine tumours based on where they grow. These include: 

• Gastrointestinal NETs: These tumours develop in the digestive system and may occur in the stomach, small intestine, appendix, colon or rectum. They are among the more common types of NETs⁶.
• Pancreatic NETs: These are also known as islet cell tumours and start in the pancreas (an organ located behind the stomach, which produces hormones like insulin). These are among the rare types of pancreatic cancer . Examples: Insulinomas, glucagonomas, gastrinomas, etc⁷.
• Lung NETs: These tumours begin in the neuroendocrine cells of the lungs. They include typical carcinoids, which generally grow slowly and are less likely to spread, and atypical carcinoids, which tend to grow faster and have a greater chance of spreading to other parts of the body⁸.
• Other NETs: NETs can also occur in areas such as the adrenal glands, thyroid gland, and skin. Examples include pheochromocytoma, medullary thyroid cancer, Merkel cell carcinoma, etc².

Grades and Stages of Neuroendocrine Tumours

The grade and stage of a neuroendocrine tumour (NET) describe two aspects. Grade helps doctors understand how quickly the tumour cells are growing and how aggressive they look under a microscope. Stage describes how large the tumour is and whether it has spread to nearby lymph nodes or other parts of the body. 

Tumour Grades

Grading of a tumour can be determined by different factors such as: 

• How fast they are growing and multiplying 
• Do they look similar to normal cells (well-differentiated) or different from normal cells (poorly differentiated) 

Well-differentiated tumours are less aggressive than poorly differentiated ones. 

Based on these, grades of NETs are: 

• Grade 1 (G1): These tumours usually grow and divide slowly and tend to be less aggressive (well differentiated and low grade). 
• Grade 2 (G2): These tumours grow at a higher rate than grade 1 tumours and are considered to be moderately aggressive (well differentiated and intermediate grade). 
• Grade 3 (G3): These tumours have a high growth and multiplication rate. Some G3 tumours are well-differentiated (less aggressive) and are called neuroendocrine cancers (NETs), while others are poorly differentiated and are highly aggressive, and are called neuroendocrine carcinomas (NECs)⁹.

Stages of NETs

The stages of NETs include: 

NETs are generally staged using the TNM system, which considers: 

• T: the size and/or local extent of the primary tumour 
• N: whether nearby lymph nodes are involved 
• M: whether the tumour has spread to distant organs⁹.

Symptoms of Neuroendocrine Tumours

Neuroendocrine tumour symptoms can vary based on the type and grade. Some people may not even notice any symptoms in the early stages. The possible symptoms of NETs are mentioned below. 

Symptoms related to Gastrointestinal /Intestinal NETs 

• Changes in bowel habits (constipation or hard stool, watery diarrhoea, bowel obstruction) 
• Nausea or vomiting 
• Abdominal pain/discomfort 
• Indigestion 
• Yellowing of skin (jaundice) 
• Unexplained weight loss 
• Unexplained weakness or fatigue 
• Rectal bleeding¹

Symptoms Related to Pancreatic NETs 

• Unexpected diabetes/ sudden variations in blood sugar levels (low or high) 
• Jaundice 
• Diarrhoea 
• Back pain 
• Peptic ulcers 
• Rashes 
• Unexplained weight loss¹

Symptoms Related to Lung NETs 

• Breathing difficulty 
• Wheezing 
• Frequent chest infections 
• Unexplained tiredness 
• Cough (sometimes with blood)¹

Symptoms Related to Carcinoid Tumour 

• Wheezing 
• Flushing (sudden warmth and redness over the face or upper body) 
• Heart palpitations or rapid heartbeat 
• Severe or watery diarrhoea 
• Abdominal pain or cramping³

Note: The symptoms listed above can occur with many different health conditions and do not necessarily indicate a neuroendocrine tumour. Some NETs may cause no noticeable symptoms, especially in the early stages. If you have persistent, unusual, or worsening symptoms, consult a qualified doctor for proper evaluation and diagnosis. It is wiser to avoid self medications and undergoing multiple investigations without seeking an opinion from an expert doctor. 

Causes of Neuroendocrine Tumours

NETs can occur for different reasons. The following are the possible causes of neuroendocrine tumours: 

• Inherited Conditions: Some NETs are associated with inherited conditions that run in families. Examples: Multiple endocrine neoplasia 1 (MEN1), neurofibromatosis type 1, Von Hippel-Lindau (VHL), etc¹⁰.
• Sporadic Cases: Most NETs occur during lifetime of an individual due to DNA mutations and altered cellular mechanisms that allow abnormal cells to survive and multiply¹¹.

Risk Factors

Factors which increase the risk of getting a disease are called a risk factors. The following are some risk factors of NETs: 

• Smoking: Smoking can increase the risk of certain NETs, especially lung-related. 
• Age: Though people of any age can get NETs or NECs, people over 55 years are at greater risk. 
• Alcohol: Alcohol is associated with risk of NETs. 
• Stomach Inflammation: Long-term inflammatory conditions such as atrophic gastritis are said to increase the risk of stomach NETs. 
• Family History: Having close family members with certain NETs or related inherited conditions can increase the likelihood of developing some types of NETs. 
• Diabetes: High blood sugar levels can increase the risk of pancreatic NETs¹⁰.

Note: Having one or more of these risk factors does not mean that a person will develop a NET. NETs can occur in people without any known risk factors, and the level of risk may vary depending on the type and location of the tumour. If you are concerned about your risk, speak with a qualified doctor. 

Diagnosis of Neuroendocrine Tumours

Diagnosing a NET may involve several tests. The following are the methods usually used by doctors to diagnose NETs: 

• Physical Examination: The doctor might check the abdomen for swelling, tenderness or a lump and look for signs such as jaundice, skin changes, or enlarged lymph nodes. They might also enquire about other symptoms like tiredness, coughing or breathing difficulties¹. Depending on the symptoms, the doctor may also examine other parts of the body. 
• Medical History: The doctor may ask about previous illnesses, existing health conditions and any history of tumours. They may also ask whether close family members have had NETs or inherited conditions linked to them¹⁰. 
• Biochemical Tests: Blood or urine tests may be used to look for hormones or other substances produced by NETs. The tests chosen depend on a person’s symptoms and the suspected type of NET. Some tests look for specific hormones or substances linked to certain NETs, while others, such as chromogranin A (non-specific), which may be used as a screening test.
• Hormone Test: If the tumour is suspected to produce hormones, the doctor may check hormone levels in the blood or urine. For example, a 24-hour urine test for 5-hydroxyindole acetic acid (5-HIAA), a substance made when the body breaks down serotonin, may be done if carcinoid syndrome is suspected⁵.
• Other Blood Tests: The doctor might recommend blood tests to check for organ function, like liver, kidney, and blood cells (platelets, red blood cells, etc.). 
• Imaging Tests: Imaging tests such as computed tomography (CT), magnetic resonance imaging (MRI), positron emission tomography (PET) scan, and ultrasound may be recommended to find a tumour, determine its size, and check whether it has spread. The doctor might also recommend some specialised tests such as somatostatin receptor imaging, which may help identify certain NETs. 
• Endoscopy: Based on the symptoms and type of suspected NET, the doctor might suggest tests to look closely, such as endoscopy to view the inside of the stomach, bronchoscopy to look inside the lungs, and colonoscopy to look inside the bowel. All of these will involve a long tube with a small camera attached at its end, which will be introduced by the doctor through the respective routes. 
• Biopsy: The doctor might remove a small portion of the suspected tumour and send it to the laboratory for confirmation. A biopsy is usually performed during endoscopy. A biopsy specimen can be valuable in confirming the disease, further, it helps with definitive classification and grading of disease. 
• Genetic Testing: This may be suggested when the doctor suspects an inherited condition. A genetic study might be helpful to determine risk of involvement of other organs at times, and risk of having similar disease amongst different family members¹².

Note: Not everyone with possible NET symptoms will need the same tests. The doctor might choose the tests based on your symptoms, overall health and where the tumour may be located. Only a qualified doctor can decide which tests are appropriate for you. 

Neuroendocrine Tumour Treatment Options

The treatment option for NET depends on the type, stage, and grade. The following are some common treatments suggested by doctors for NET: 

• Active Surveillance: The doctor might not recommend immediate treatment for some small, slow-growing NETs, such as small non functioning pancreatic NETs. Instead, they may monitor the tumour regularly with scans, blood tests or other examinations and start treatment if it shows signs of growth¹³.
• Surgery: Surgery may be recommended when the tumour can be safely removed. This the most common treatment. The surgeon might remove the tumour and, when necessary, some of the surrounding tissue or nearby lymph nodes^6,14.
• Somatostatin analogues: These are medicines that help control symptoms caused by excess hormones. They may also slow the growth of some NETs. Examples: Octreotide and lanreotide. 
• Targeted Therapy: This is a treatment which uses certain medicines that act on specific features of tumour cells to slow or stop their growth. Examples: Everolimus and sunitinib. 
• Chemotherapy: In this treatment, certain medicines are used to destroy or slow the growth of rapidly dividing tumour cells. Chemotherapy may be considered for some aggressive or advanced NETs. Some of The drugs can be given orally. Examples: Temozolomide and capecitabine. 
• Peptide Receptor Radionuclide Therapy (PRRT): This treatment uses a radiolabeled somatostatin receptor-targeting peptide targets specific receptors found on some NET cells. The radioactive material then delivers radiation directly to these cells. Examples of radioactive substances are lutetium-177 and yttrium-90¹⁴. 
• Radiation Therapy: This treatment uses high-energy X-rays to destroy or kill tumour cells. It may be considered for some NETs such as gastrointestinal NETs.The therapy is mostly external , where the radiation is given to the affected body part using a machine⁶.
• Liver-Directed Treatments: When a NET has spread to the liver, doctors may consider treatments such as radiofrequency ablation, which uses heat made by radio waves to control or destroy tumours in the liver. In severe cases, they might also recommend a liver transplant¹⁴.

How to Prevent Neuroendocrine Tumours?

An NET cannot always be prevented. However, maintaining a healthy lifestyle and being aware of personal risk factors may support overall health. The following are some ways which may help reduce the risk: 

• Avoid smoking and reduce the consumption of alcohol. 
• Maintain a healthy body weight. 
• Manage underlying conditions such as diabetes¹⁰.
• Know your family history of any genetic disease and discuss it with your doctor for any genetic screening. 
• Notice ongoing symptoms and consult your doctor for proper diagnosis. 

Note: NETs cannot always be prevented, and these tips do not guarantee that you can avoid them. If you have ongoing symptoms or concerns about your risk, speak with a qualified doctor for personalised advice and appropriate screening. 

When to Consult a Doctor?

Consulting a doctor is very important if you have ongoing stomach pain, diarrhoea, unexplained weight loss, repeated flushing, tiredness, breathing problems, or unusual hormone-related symptoms¹. It is also important to seek medical advice if you have a strong family history of NETs or related genetic conditions¹⁰. Getting checked can help with the proper diagnosis and treatment, if needed. 

Also Read: Stomach Cancer: Symptoms, Causes, Stages, Types & Treatment

Conclusion

NETs are uncommon cancers that can start in different parts of the body and may affect each person differently. Their symptoms and treatment depend on where the tumour develops, how fast it grows, and whether it makes hormones. Most NETs cannot be prevented, but knowing the risk factors and getting persistent symptoms checked can help with early diagnosis and proper care. 

Frequently Asked Questions (FAQs)

References

1. What are the symptoms of neuroendocrine tumours? Cancer Australia. 2024. Available from: https://www.canceraustralia.gov.au/cancer-types/neuroendocrine-tumours/what-are-symptoms-neuroendocrine-tumours 

2. Definition of neuroendocrine tumor. NCI.  Available from:  https://www.cancer.gov/publications/dictionaries/cancer-terms/def/neuroendocrine-tumor 

3. Neuroendocrine tumors and carcinoid Tumors. American Cancer Society. 2025.  Available from:  https://www.cancer.org/cancer/types/carcinoid-neuroendocrine-tumors.html 

4. Neuroendocrine spore. NCI. 2025.  Available from: https://dctd.cancer.gov/research/spores/focus-area/neuroendocrine 

5. Raphael MJ, Chan DL, Law C, Singh S. Principles of diagnosis and management of neuroendocrine tumours. CMAJ. 2017;189(10):E398-E404. doi:10.1503/cmaj.160771. Available from: https://www.cmaj.ca/content/189/10/e398

6. Gastrointestinal neuroendocrine tumors treatment. NCI. 2025.  Available from: https://www.cancer.gov/types/gi-neuroendocrine-tumors/patient/gi-neuroendocrine-treatment-pdq 

7. What is a pancreatic neuroendocrine tumor? American Cancer Society. 2025. Available from:  https://www.cancer.org/cancer/types/pancreatic-neuroendocrine-tumor/about/what-is-pnet.html 

8. Lung neuroendocrine tumor. American Cancer Society. 2025.  Available from: https://www.cancer.org/cancer/types/lung-carcinoid-tumor.html 

9. Grading & staging. Neuroendocrine Cancer Australia.  Available from: https://neuroendocrine.org.au/understanding-neuroendocrine-cancer/what-are-neuroendocrine-cancers/grading-staging/ 

10. Risks and causes of neuroendocrine cancer. Cancer Research UK. 2025.  Available from: https://www.cancerresearchuk.org/about-cancer/neuroendocrine-tumours-nets/risks-causes 

11. Oncogenes, tumor suppressor genes, and DNA repair genes. American Cancer Society. 2026.  Available from: https://www.cancer.org/cancer/understanding-cancer/genes-and-cancer/oncogenes-tumor-suppressor-genes.html

12. Tests to diagnose neuroendocrine cancer. Cancer Research UK. 2025.  Available from: https://www.cancerresearchuk.org/about-cancer/neuroendocrine-tumours-nets/getting-diagnosed/tests-diagnose 

13. Maratta MG, Chiloiro S, Raia S, et al. Somatostatin analogs versus active surveillance in small pancreatic neuroendocrine tumors. Pancreas. 2024;54(6):e524-e529. doi:10.1097/MPA.0000000000002425. Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC12175780/ 

14. Treatment options for neuroendocrine cancer. Cancer Research UK.  Available from: https://www.cancerresearchuk.org/about-cancer/neuroendocrine-tumours-nets/treatment/options#treatment-for-neuroendocrine-tumours-(nets) 

15. Life Expectancy with neuroendocrine cancer: Survival rates.  Available from: https://neuroendocrine.org.au/resources/net-information/life-expectancy/ 

16. Signs and symptoms of gastrointestinal neuroendocrine tumors. American Cancer Society. 2025.  Available from: https://www.cancer.org/cancer/types/gastrointestinal-carcinoid-tumor/detection-diagnosis-staging/signs-symptoms.html 

Disclaimer: The information provided here is for educational/awareness purposes only and is not intended to be a substitute for medical treatment by a healthcare professional and should not be relied upon to diagnose or treat any medical condition. The reader should consult a registered medical practitioner to determine the appropriateness of the information and before consuming any medication. PharmEasy does not provide any guarantee or warranty (express or implied) regarding the accuracy, adequacy, completeness, legality, reliability or usefulness of the information; and disclaims any liability arising thereof. 

Links and product recommendations in the information provided here are advertisements of third-party products available on the website. PharmEasy does not make any representation on the accuracy or suitability of such products/services. Advertisements do not influence the editorial decisions or content. The information in this blog is subject to change without notice. The authors and administrators reserve the right to modify, add, or remove content without notification. It is your responsibility to review this disclaimer regularly for any changes.