Causes and Risk Factors of Carcinoid Tumors

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Carcinoid tumors are rare, slow-growing neuroendocrine tumors (NETs) that usually develop in the digestive, or gastrointestinal (GI) tract, such as the stomach or intestines, or in the lungs. In some cases, a carcinoid tumor develops in another part of the body, such as the pancreas, the testicles, or ovaries.

Carcinoid tumors are considered to be "cancer in slow motion," as many progress very slowly. If you have a carcinoid tumor, you may have it for years and never know it. Since carcinoid cancers grow very slowly, they are usually not diagnosed until ages 55–65.

Among carcinoid tumors, gastrointestinal tumors make up 60% of all neuroendocrine tumors.

This article will discuss the causes and modifiable and unmodifiable risk factors of carcinoid tumors and what you can do to decrease your risk.

Multi ethnic research team studying DNA mutations. Female doctor in foreground

janiecbros / Getty Images

Causes

Although scientists do not specifically know what causes carcinoid tumors, many tumors occur when cells develop mutations in their hereditary material, or DNA (deoxyribonucleic acid). Whereas healthy cells would normally die over time, the mutations in these cells enable them to grow and divide uncontrollably. As these mutated cells accumulate, they grow into clumps of cells known as tumors and may invade nearby tissues (metastasize).

Genetics

Some DNA mutations, known as familial mutations, can be passed on in families. A small number of carcinoid tumors are caused by inherited gene mutations. Scientists have discovered that changes in four tumor suppressor genes are responsible for many inherited cases of carcinoid tumors.

Tumor suppressor genes make proteins that regulate the growth of cells, and they play an important role in preventing the development of cancer cells. When tumor suppressor genes are altered or inactivated, unchecked growth of damaged or abnormal cells occurs, which leads to uncontrolled growth and the development of cancerous tumors.

These tumor suppressor genes include:

  • MEN1 (multiple neuroendocrine neoplasia 1) gene: Multiple neuroendocrine neoplasia 1 is a rare group of endocrine tumors. Changes in the MEN1 gene for most inherited cases. Some studies have shown that MEN1 leads to a higher chance of developing bronchial and intestinal carcinoid tumors. It is estimated that about 5%–10% of carcinoid tumors come from mutations in MEN1.

A smaller number are caused by inherited changes in the following genes:

  • NF1 (Neurofibromatosis type 1) gene: Defects in NF1 cause neurofibromatosis type 1, a genetic disease that forms neurofibromas, which are benign tumors that develop in nerves under the skin and in other parts of the body. Some people with this condition also develop carcinoid tumors of the small intestines.
  • VHL (von Hippel–Lindau) gene: Von Hippel-Lindau are rare, inherited disorders that cause tumors to grow in certain parts of the body, including the brain, spinal cord, eyes, inner ear, adrenal glands, pancreas, kidney, and reproductive tract. Defects in the VHL gene can contribute to pancreatic neuroendocrine tumors (PNETs).
  • TSC1 or TSC2 (tuberous sclerosis complex 1 or 2) genes: Tuberous sclerosis complex can be caused by a defect in the TSC1 or TSC2 gene. People with this condition can also develop carcinoid tumors of the heart, eyes, brain, lungs, and skin.

Prevention

There is no way to prevent carcinoid tumors. However, treating carcinoid tumors early may help you prevent the symptoms of carcinoid syndrome.

Unmodifiable Risk Factors

A risk factor is anything that increases a person’s chance of developing a disease such as cancer. Unmodifiable risk factors are those that cannot be changed. Some unmodifiable risk factors for carcinoid tumors include:

  • Race and gender: Carcinoid cancers are more common In Black people than white people. They are also slightly more common in women than in men.
  • Gastric diseases (pernicious anemia): Pernicious anemia is an autoimmune condition in which the body can’t absorb vitamin B12 correctly. This type of anemia results in very large, malformed red blood cells. It also causes a reduced number of functioning red blood cells in the body.
  • Age: For gastrointestinal carcinoid tumors, the average age at diagnosis is 55–65. Children rarely develop neuroendocrine tumors.
  • Sporadic mutations: Some carcinoid tumors are caused by sporadic changes (mutations) in oncogenes, or tumor suppressor genes. Mutations are called sporadic if they occur after a person is born, rather than having been inherited.

People with pernicious anemia have a higher risk of developing NETs of the stomach. This is thought to be due to chronic inflammation and irritation of the epithelial cells that line and mucosa that line the stomach.

Lifestyle Risk Factors

In cancer, the important lifestyle risk factors that affect the incidence (frequency) and mortality (number of deaths) of the disease include environmental pollutants, radiation, tobacco, alcohol, diet, obesity, and infectious agents, such as bacteria or viruses). Race, gender, and age are also important risk factors in cancer development and progression.

It is important to note that risk factors do not necessarily indicate that a person will develop a specific type of cancer. People with no risk factors at all can still acquire diseases, including cancer. As well, those having one (or even several) risk factors may never get a disease. Lifestyle risk factors include modifiable risk factors.

Modifiable Risk Factors

Modifiable risk factors are those that can be changed. For carcinoid tumors, the primary modifiable risk factors involve exposure to environmental pollutants. This is usually related to a person’s occupation and where they live, such as rural, suburban, or urban communities.

Less is known about other lifestyle risk factors, such as:

  • Radiation
  • Tobacco
  • Alcohol
  • Diet
  • Infectious agents

Reducing your exposure to environmental pollutants can greatly improve your quality of life and decrease the formation of carcinoid tumors. Recent studies have shown that environmental exposures from mining, agriculture, and other industries may lead to a rise in small intestinal carcinoid tumors (SINT). Additionally, early exposure to environmental pollutants from coal and uranium appears to increase the risk of carcinoid tumors.

Environmental Pollutants May Lead to an Increase in SINTs

In one study involving carcinoid tumors, researchers looked at people ages 23–88 who were diagnosed with small intestinal carcinoid tumors from 1948 to 2014, while living in different environments in Utah. Their findings suggest that the incidence of SINT is twice as likely in people who live in large, urban locations that are close to industrial and mining areas than in less urban environments.

Summary

Carcinoid tumors are rare, slow-growing neuroendocrine tumors that usually develop in the digestive tract or in the lungs. In some cases, a carcinoid tumor develops in another part of the body, such as the pancreas, testicle, or ovary.

Although scientists do not specifically know what causes carcinoid tumors, many tumors occur when cells develop mutations in their DNA. The mutations enable cells to grow and divide uncontrollably, whereas healthy cells would normally die over time. As these mutated cells accumulate, they grow into clumps of cells known as tumors and may invade nearby tissues or metastasize.

Carcinoid tumor risk factors include modifiable (environment) and unmodifiable (race and gender,having other gastric diseases) risk factors. Reducing your exposure to environmental pollutants can greatly improve your quality of life and reduce the chance of forming carcinoid tumors.

A Word From Verywell

A carcinoid tumor diagnosis can be frustrating and upsetting, especially when experts are unsure of the exact cause of the disease. Fortunately, medical research continues to reveal new and more effective treatments that are aimed at improving survival rates. As the incidence of carcinoid tumors continues to rise, it is important to note that these neuroendocrine tumors remain relatively rare and have a good prognosis.

That said, scientists and researchers continue to make strides in finding new ways to prevent and treat cancer. Specifically, more efforts are aimed at slowing down the progression of the disease, which would give patients more years of living a healthy, symptom-free life.

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10 Sources
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