Pulmonary carcinoid tumour is a rare form of lung cancer that begins in specialised neuroendocrine cells deep within the lungs, growing slowly in most cases and offering better prospects than many other lung malignancies.
When most people think of lung cancer, they picture aggressive diseases linked to smoking and rapid decline. But pulmonary carcinoid tumours represent a different story altogether. These uncommon cancerous growths arise from neuroendocrine cells, which are special cells in the lungs that act like both nerve and hormone-producing cells. These cells help manage important lung functions, such as controlling airflow, regulating blood flow, monitoring oxygen and carbon dioxide levels, and even influencing how other lung cells grow and divide.
Unlike more common lung cancers, carcinoid tumours typically develop more slowly and behave less aggressively. Many patients live for years or even decades after diagnosis, especially when the tumour is caught early. Yet despite their relatively better outlook, these are still true cancers that require proper medical attention and treatment. Understanding what makes them different helps patients and families navigate the journey with more clarity and less fear.
How Common Are Lung Carcinoid Tumours
Lung carcinoid tumours stand out for their rarity. Only about 1% to 2% of all lung cancers fall into this category. In the United States, doctors diagnose somewhere between 2,000 and 4,500 new cases each year. To put this in perspective, tens of thousands more people are diagnosed annually with other types of lung cancer, making carcinoid tumours a truly uncommon finding.[1]
The incidence of lung carcinoid tumours has been rising slightly in recent years compared to other neuroendocrine tumours, though researchers are still working to understand why this increase is occurring. Part of the rise may simply reflect better detection methods, as more chest scans are performed for various reasons and more small tumours are spotted incidentally before they cause any symptoms.[3]
These tumours can develop in anyone, but certain patterns emerge when looking at who is most commonly affected. Women appear to be at slightly higher risk than men. The most common age at diagnosis falls between 45 and 55 years old, though these tumours can appear at any age, including in children and young adults. There is no strong geographic pattern, though carcinoid tumours appear somewhat more frequently in white populations compared to other racial and ethnic groups.[1][7]
About one in three carcinoid tumours that occur anywhere in the body starts in the lungs. The rest develop in other organs, particularly the digestive system, appendix, kidneys, and other sites where neuroendocrine cells naturally exist.[1]
What Causes Lung Carcinoid Tumours
The precise cause of lung carcinoid tumours remains something of a mystery. Scientists know that these growths begin when neuroendocrine cells in the lungs start multiplying out of control. Normal cells follow strict rules about when to divide and when to stop. But in carcinoid tumours, something goes wrong with the genetic instructions inside these cells, causing them to ignore the usual stop signals and keep reproducing.
As these abnormal cells accumulate, they form small clusters called tumorlets. Over time, these tiny clusters can grow into larger masses that doctors identify as carcinoid tumours. Depending on how the cells look under a microscope and how they behave, they might be classified as typical carcinoid tumours, atypical carcinoid tumours, or even more aggressive types of neuroendocrine cancers.[1]
What triggers this initial malfunction in the cell’s DNA remains unclear. Unlike many other lung cancers, where smoking is the primary culprit, the connection between smoking and carcinoid tumours is much weaker. Typical carcinoid tumours, which make up the vast majority of cases, don’t appear to be strongly linked to smoking at all. However, atypical carcinoid tumours, which are more aggressive, are found somewhat more often in people who smoke.[1][7]
Risk Factors for Developing Lung Carcinoid Tumours
While the exact cause remains unknown, certain factors seem to increase a person’s likelihood of developing these tumours. The most significant known risk factor is having a rare inherited condition called multiple endocrine neoplasia type 1, or MEN1. People with this genetic disorder have mutations that make them prone to developing tumours in various hormone-producing glands throughout the body, including the lungs.[1][7]
Beyond MEN1, other risk factors are less clearly defined. Being female appears to confer slightly higher risk, though the reasons for this gender difference are not well understood. Age matters too, with most cases occurring in middle-aged adults between 45 and 55, though younger and older individuals can certainly develop these tumours as well.
As mentioned earlier, smoking may play a role in atypical carcinoid tumours specifically, though the association is not as strong as it is with other lung cancers. Some research suggests that smoking may affect how aggressive the tumour becomes or how well a patient responds to treatment, even if it didn’t directly cause the tumour to form in the first place.[6]
Family history beyond MEN1 is not clearly established as a major risk factor, though having close relatives with carcinoid tumours may slightly increase risk. Unlike many other cancers, there are no clear environmental or occupational exposures that have been definitively linked to lung carcinoid development.
Symptoms of Lung Carcinoid Tumours
One of the challenging aspects of lung carcinoid tumours is that they often don’t announce themselves with obvious symptoms. In fact, roughly a quarter of patients have no symptoms at all when their tumour is discovered. These cases are typically found by accident when someone has a chest X-ray or CT scan for an entirely different reason, such as checking on pneumonia or investigating an unrelated health concern.[3]
When symptoms do appear, they tend to develop gradually and can easily be mistaken for other common respiratory problems. A persistent cough is one of the most frequent complaints. This cough may occasionally produce blood or mucus, which understandably causes alarm. Chest pain, though often mild at first, can occur as the tumour grows or affects surrounding tissues.[1][4]
Breathing difficulties form another common symptom cluster. Patients may notice shortness of breath, especially during physical activity. Wheezing can occur when the tumour partially blocks one of the airways, creating a whistling or rattling sound as air tries to squeeze through the narrowed passage. Some people experience recurrent bouts of pneumonia in the same part of the lung, which happens because the tumour blocks normal drainage and creates a space where bacteria can thrive.[3]
In rare cases, lung carcinoid tumours produce large amounts of hormones, particularly serotonin, which is a chemical messenger that affects various body systems. When this happens, patients may develop carcinoid syndrome, a collection of symptoms that includes severe diarrhea, sudden flushing or warmth in the face and neck, unexpected weight gain, and worsening breathing problems that mimic asthma. Carcinoid syndrome occurs much less frequently with lung carcinoids than with carcinoid tumours in the digestive system, and it typically only appears when tumours are very large or have already spread to other parts of the body.[1][4]
Some patients also develop other unusual symptoms related to hormone production, similar to those seen with small cell lung cancer. These might include features of Cushing’s syndrome if the tumour makes hormones that affect cortisol levels, though this is uncommon.[5]
How Lung Carcinoid Tumours Are Different From Each Other
Not all lung carcinoid tumours behave the same way. Doctors divide them into two main types based on how the cells look under a microscope and how aggressively they grow: typical and atypical.
Typical carcinoid tumours account for about 85% to 90% of all lung carcinoid cases. These are the slower-growing, less aggressive variant. They rarely spread beyond the lungs to other organs, though they can occasionally reach nearby lymph nodes. Under the microscope, typical carcinoid cells look fairly organized and well-differentiated, meaning they still resemble normal lung cells in many ways. The outlook for people with typical carcinoid tumours is generally quite good, with 85% to 90% surviving at least five years after diagnosis.[1][7]
Atypical carcinoid tumours make up the remaining 10% to 15% of cases. These grow faster and behave more aggressively. They have a higher chance of spreading to other organs, including the liver, bones, or brain. Under the microscope, atypical carcinoid cells look more abnormal and disorganized, with more frequent cell division and areas of dead tissue. The five-year survival rate for atypical carcinoid is lower, ranging from 50% to 70%, reflecting their more aggressive nature.[1][7]
Another way to describe these tumours involves their location within the lungs. Central carcinoids develop in the large airways near the centre of the chest. These may be more likely to cause symptoms like coughing or wheezing because they can block major airways. Peripheral carcinoids grow in the smaller airways near the outer edges of the lungs and may remain silent for longer periods because they don’t interfere with major airflow passages. Atypical carcinoids are more often peripheral, though they can appear in either location.[1]
Preventing Lung Carcinoid Tumours
Because the exact causes of lung carcinoid tumours remain unknown, there are no proven strategies to prevent them from developing. Unlike some other lung cancers where avoiding tobacco definitively reduces risk, the weak connection between smoking and carcinoid tumours means that even lifelong non-smokers can develop these growths.
That said, maintaining overall lung health remains important. If you do smoke, quitting offers numerous health benefits beyond cancer prevention, including better cardiovascular health, improved breathing, and enhanced ability to recover from surgery or other treatments if a tumour is found. Avoiding secondhand smoke and occupational lung irritants also contributes to better respiratory health overall.
For individuals with multiple endocrine neoplasia type 1, regular screening and monitoring by healthcare professionals familiar with the condition may help catch tumours earlier when they’re easier to treat, though this isn’t prevention in the traditional sense.
There are no specific dietary supplements, lifestyle changes, or screening tests currently recommended for preventing lung carcinoid tumours in the general population. Regular health check-ups and promptly reporting any persistent respiratory symptoms to your doctor remain the best approach for early detection.
How Lung Carcinoid Tumours Change Normal Body Functions
To understand how carcinoid tumours affect the body, it helps to know what neuroendocrine cells normally do. These remarkable cells scattered throughout the lungs have a dual nature. On one hand, they act like nerve cells, receiving signals from the nervous system about the body’s needs. On the other hand, they function like endocrine cells, responding to those signals by releasing hormones and other chemical messengers.
In healthy lungs, neuroendocrine cells help maintain a delicate balance. They participate in regulating airflow by influencing the muscles around airways, adjusting blood flow through lung vessels, monitoring oxygen and carbon dioxide levels in the air, and even influencing how quickly other lung cells grow and replace themselves. It’s a complex system that normally works seamlessly in the background.[1]
When neuroendocrine cells become cancerous and form a carcinoid tumour, several things can go wrong. First, the physical presence of the tumour can cause mechanical problems. If the growth occurs in a major airway, it acts like a partial roadblock, making it harder for air to flow in and out. This explains the wheezing and shortness of breath that some patients experience. The blockage can also trap mucus behind it, creating a breeding ground for bacteria and leading to repeated infections in the same lung area.
Second, carcinoid tumours are often very vascular, meaning they develop a rich blood supply. This makes them prone to bleeding, which is why some patients cough up blood. The tumours appear pink or purplish in color because of all the blood vessels running through them. They usually grow with intact lung tissue covering them, at least initially, giving them a smooth surface that can sometimes be seen during bronchoscopy, a procedure where doctors look inside the airways with a camera.[5]
Third, because these tumours come from hormone-producing cells, they sometimes make and release excessive amounts of various substances. The most notable is serotonin, which can cause carcinoid syndrome when present in large quantities. The flushing, diarrhea, and other symptoms of this syndrome all stem from too much serotonin circulating through the body. However, this typically only happens when the tumour is quite large or has spread to the liver, because the liver normally breaks down excess serotonin before it can cause problems.
As carcinoid tumours grow, they can also cause local tissue damage. They may invade into the bronchial wall and surrounding lung tissue, even though they usually do this more slowly than other lung cancers. In advanced cases, tumours can spread to nearby lymph nodes or travel through the bloodstream to distant organs like the liver, bones, or brain. When this metastasis occurs, it can disrupt the function of those organs as well.
Some tumours produce small satellite clusters called tumorlets in nearby areas, though it’s unclear whether these represent early metastases or simply other areas where neuroendocrine cells are misbehaving. When present, tumorlets may indicate a somewhat more aggressive tumour that requires closer monitoring.[5]
Complications can develop even with typical slow-growing carcinoids. Pneumonia can become recurrent when airways remain partially blocked. Complete airway obstruction can cause a section of the lung to collapse. The tumour itself can bleed into the airway. And if carcinoid syndrome develops, the chronic diarrhea and other symptoms can significantly impair quality of life and lead to nutritional deficiencies.[1]