Neuroendocrine tumours are rare cancers that can develop almost anywhere in the body, most commonly in the digestive system, lungs, or pancreas, and while they can be serious, many grow slowly and can be managed for years with the right treatment and care.

Understanding Neuroendocrine Tumours

Neuroendocrine tumours, often called NETs, are unusual cancers that begin in special cells scattered throughout the body. These cells are unique because they share features of both nerve cells, which send and receive signals from the brain, and hormone-making cells that help regulate different body functions. Most neuroendocrine tumours are malignant, which means they are cancerous, but they often behave differently from other cancers people may be more familiar with.^[1]

These tumours can appear in many parts of the body, but they have a preference for certain areas. The digestive system is the most common location, particularly the intestines, appendix, rectum, stomach, and pancreas. The lungs are the second most frequent site. Less often, NETs can develop in the thyroid gland, adrenal glands, pituitary gland, or other organs where these special neuroendocrine cells are found.^[2]

What makes neuroendocrine tumours particularly complex is their variety. Some NETs are called functional tumours because they produce excess hormones that cause noticeable symptoms. Others are non-functional tumours, meaning they don’t release enough hormones to cause symptoms, though they can still create problems if they grow large enough to press on nearby organs.^[1]

How Common Are Neuroendocrine Tumours

Neuroendocrine tumours are considered rare in the medical world. Worldwide, they affect approximately six out of every one hundred thousand people. While this may sound like a very small number, the diagnosis of NETs has been increasing in recent years. This rise is likely not because more people are developing these tumours, but because doctors have better tools and tests to identify them earlier than they could in the past.^[2]

These tumours are uncommon in younger people. Children, teenagers, and young adults rarely develop NETs. Most people who receive this diagnosis are between the ages of fifty and sixty years old. Anyone can potentially develop a neuroendocrine tumour, but the risk increases as people get older.^[2]

The digestive tract accounts for just over half of all neuroendocrine tumour cases, with the large bowel and appendix being particularly common sites. The lungs are the location for about one quarter of cases. The pancreas and stomach account for smaller percentages. This distribution helps doctors understand where to look when they suspect a patient might have a NET.^[8]

What Causes Neuroendocrine Tumours

The exact cause of neuroendocrine tumours remains a mystery to medical researchers. What doctors do know is that NETs begin when neuroendocrine cells start to divide and multiply in an uncontrolled way. Over time, these abnormal cells form masses called tumours. These tumours can then affect the organs where they’re located. However, scientists haven’t yet discovered what triggers this abnormal cell behaviour in the first place.^[2]

Unlike some diseases that can be traced to specific behaviours or exposures, neuroendocrine tumours don’t appear to have clear preventable causes. This can be frustrating for patients who naturally wonder “Why did this happen to me?” or “What could I have done differently?” The current understanding is that these tumours develop somewhat randomly in most cases.^[8]

Because NETs often grow slowly, the body may have been dealing with them for years before any symptoms appear or before they’re discovered during medical tests. This long, quiet growth period means that by the time someone feels unwell enough to see a doctor, the tumour may have been present for quite some time.^[23]

Risk Factors for Neuroendocrine Tumours

While most neuroendocrine tumours develop without any known risk factors, researchers have identified certain rare inherited conditions that increase a person’s chances of developing NETs. These are genetic syndromes caused by changes, or mutations, in specific genes that are passed down through families.^[2]

One such condition is called Multiple Endocrine Neoplasia, or MEN for short. This syndrome causes overactive tumours to form in various organs and glands that make hormones. Type 1 MEN, also written as MEN1, is the most common inherited cancer syndrome linked to neuroendocrine tumours. People with this condition need regular monitoring by their doctors.^[2]

Other genetic conditions that raise the risk include Von Hippel-Lindau disease and neurofibromatosis. However, it’s important to understand that having one of these syndromes doesn’t guarantee someone will develop a NET—it simply means they face a higher risk than the general population. Most people with NETs do not have any of these genetic conditions. The vast majority of cases are described as “sporadic,” meaning they occur randomly without being related to another disease or inherited from parents.^[8]

Symptoms of Neuroendocrine Tumours

One of the challenges with neuroendocrine tumours is that they often don’t cause symptoms in their early stages. Many people feel perfectly fine until the tumour grows large enough to press on an organ or until it produces enough hormones to affect how the body works. This is why NETs are sometimes discovered by accident during tests or scans performed for completely unrelated reasons.^[2]

When symptoms do appear, they vary greatly depending on where the tumour is located in the body. A NET in the digestive system might cause stomach pain, diarrhoea, nausea, or vomiting. People with lung NETs might experience shortness of breath or a persistent cough, sometimes with blood. General symptoms that can occur regardless of location include feeling unusually tired all the time, which doctors call fatigue.^[2]

Some neuroendocrine tumours that produce hormones create a specific pattern of symptoms called carcinoid syndrome. This happens when certain NETs release large amounts of hormones into the bloodstream. People with carcinoid syndrome often experience sudden reddening of the skin, especially on the face and neck, which is called flushing. They may also have severe diarrhoea, painful gas and bloating, or wheezing and shortness of breath. These symptoms can be triggered by specific foods, drinks, or even stress.^[1]

It’s crucial to remember that experiencing these symptoms doesn’t automatically mean you have cancer. Many common, less serious conditions can cause similar problems. However, if you notice symptoms that persist or worsen over time, it’s important to discuss them with a healthcare provider. Early investigation can lead to earlier diagnosis if a problem does exist.^[2]

Prevention of Neuroendocrine Tumours

Unlike some cancers where specific lifestyle changes can reduce risk—such as not smoking to prevent lung cancer—there are no known preventive measures for neuroendocrine tumours. Because researchers don’t fully understand what causes NETs to develop in the first place, they cannot yet offer specific advice on how to prevent them. This reality can feel discouraging, but it’s important to understand that developing a NET is not a result of something you did or failed to do.^[8]

For people with inherited genetic syndromes that increase NET risk, prevention takes a different form. It focuses on early detection rather than stopping tumours from forming. Regular monitoring with blood tests, imaging scans, and check-ups allows doctors to find any tumours when they’re still small and potentially easier to treat. This approach doesn’t prevent NETs, but it can significantly improve outcomes by catching problems early.^[8]

General healthy living practices remain valuable even though they don’t specifically prevent NETs. Maintaining a balanced diet, staying physically active, avoiding tobacco, and limiting alcohol all contribute to overall health and may help your body better cope with medical challenges if they arise. Regular medical check-ups also mean that if a NET does develop, there’s a better chance it will be discovered sooner rather than later.^[8]

How Neuroendocrine Tumours Affect the Body

To understand how neuroendocrine tumours affect the body, it helps to know what happens when these special cells stop working normally. Healthy neuroendocrine cells throughout the body have important jobs. They create, store, and release small proteins and hormones that the body needs for normal functions. When these cells become cancerous, they can multiply out of control and form tumours.^[8]

The way a NET affects the body depends partly on whether it’s functional or non-functional. Functional tumours produce excessive amounts of hormones. These hormones flood into the bloodstream and can cause dramatic effects throughout the body. For example, some NETs produce too much of a substance called serotonin, which affects digestion, blood flow, and mood. This excess can lead to the flushing, diarrhoea, and other symptoms of carcinoid syndrome.^[1]

Non-functional tumours cause problems in different ways. As they grow, they take up space and can press on nearby organs. A tumour in the pancreas might block ducts that carry digestive enzymes, leading to pain and digestive problems. A NET in the lung might partially block an airway, making breathing difficult. Some tumours can weaken the wall of blood vessels or organs, potentially causing serious complications.^[8]

Like other cancers, neuroendocrine tumours can spread beyond their original location, a process called metastasis. The liver is a particularly common site for NET spread, especially from tumours that started in the digestive system. When NETs reach the liver, they can interfere with this vital organ’s many functions, including filtering blood, producing proteins, and processing nutrients. This is why monitoring and treating liver involvement is often a critical part of NET care.^[8]

The growth rate of neuroendocrine tumours varies significantly. Some NETs are described as “low grade” and grow very slowly, sometimes taking years to cause serious problems. Others are “high grade” and grow more aggressively. The grade, along with how differentiated the cells appear under a microscope, helps doctors predict how the tumour might behave and what treatment approach might work best.^[6]