Carcinoid tumours are rare. There is very little information about what causes them. Doctors think that most cases happen by chance.
Anything that can increase your risk of getting a disease is called a risk factor.
Different cancers have different risk factors. Having one or more risk factors doesn't mean you will definitely get cancer. Many people who have risk factors never get cancer, and some people with no risk factors do develop cancer.
Family history and genetic syndromes
Carcinoid tumours develop more often than usual in people who have a rare family syndrome called multiple endocrine neoplasia type 1 (MEN1). Around 1 in 10 people with MEN1 (10%) develop carcinoid tumours. They are more likely to be diagnosed with carcinoid at a younger age than average. Your doctor might ask you about your family history of cancer.
A Swedish study showed that children of parents with carcinoid tumours may have a risk of carcinoid that is 4 times higher than the general population. People with a brother or sister with carcinoid may have a risk that is 3 times higher. But as carcinoid tumours are rare, this risk is still small.
The same study showed that people may have a slightly increased risk of carcinoid if they have a parent with non-Hodgkin lymphoma, or cancer of the brain, breast, liver, bladder or endocrine system. People with a brother or sister diagnosed with cancer of the bowel, brain, cervix or endocrine system also have an increased risk of carcinoid tumours.
Other studies have found that a family history of any cancer might increase the risk of carcinoid tumours.
People who have the conditions neurofibromatosis or tuberous sclerosis have a higher than normal risk of getting a carcinoid tumour.
People with von Hippel-Lindau syndrome have a higher than normal risk of developing carcinoid of the pancreas.
Carcinoid is slightly more common in black people of African descent than in white people.
Overall, slightly more women than men develop carcinoid.
People who have diabetes for a long time have an increased risk of getting carcinoid tumours. The risk is especially increased in women.
Other medical conditions
If you have had long term inflammation of the stomach lining (called chronic atrophic gastritis), you have a slightly higher risk of carcinoid of the stomach.
You also have a higher risk of stomach carcinoid if you have MEN1 or a condition called Zollinger Ellison syndrome, where the stomach lining makes too much acid.
Possible risk factors
These risk factors have been studied, but it is not clear whether they increase the risk of carcinoid tumours.
An American study has shown that people who eat a lot of saturated fat have a higher risk of carcinoid tumours of the small bowel than people who have low levels of saturated fat in their diet. But we need more research to really know whether dietary fats affect the risk of carcinoid tumours.
Smoking and alcohol
Smoking might increase the risk of carcinoid tumours. And drinking alcohol may also increase the risk of some tumours, such as those in the pancreas. But we need larger studies to be sure.
An American study has shown that people who are morbidly obese have double the risk of carcinoid tumours of the small bowel compared to those with a healthy weight. Morbidly obese means you have a body mass index (BMI) greater than 35.
Hormone replacement therapy (HRT)
The same American study has suggested that current use of hormone replacement therapy is linked with doubling the risk of carcinoid tumours of the small bowel. But more research is needed to look into the different types of hormone therapy and how long it is taken for, and its possible link with carcinoid tumours.
Other possible causes
Stories about potential causes are often in the media, but it isn’t always clear which ideas are supported by evidence. There might be things you have heard of that we haven’t included here. This is because either there is no evidence about them or because it isn't yet clear what the evidence shows.