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What Causes Lung Cancer?

Posted on January 04, 2021

Article written by Emily Wagner, M.S.

Like other cancers, lung cancer is caused by genetic mutations that allow cells to divide and grow in a disorganized way. Anything that increases the risk for developing genetic mutations can also increase your risk for lung cancer.

Genetic Mutations and Lung Cancer

There are two main types of genetic mutations — inherited and acquired.

Inherited mutations:

  • Are passed down through family, from parents to children
  • Are present in the DNA of all cells at birth
  • Occur less often than acquired mutations

Acquired mutations:

  • Accumulate over the course of a person’s life
  • Are present in the DNA of only some cells
  • Are caused by aging and exposure to cancer-causing agents (carcinogens), such as cigarette smoke, chemicals, radiation, and more

Most gene changes related to lung cancer are acquired during life, as opposed to being inherited from family. Lung cancer can run in families, but it is usually caused by environmental factors. It remains unclear why some people develop lung cancer and others do not.

Acquired Mutations Associated With Lung Cancer

Some acquired mutations are thought to play important roles in different types of lung cancer. For example, mutations in the tumor suppressor gene (TSG) RB1 are thought to be important in the development of small cell lung cancer (SCLC). Mutations in TSG p16 and the cancer-causing gene KRAS are thought to be important in the development of non-small cell lung cancer (NSCLC). Every case of lung cancer is different, and each will have different gene changes, including some that may have not been found yet.

How Cells Transform Into Cancer

Normal cells divide in a regular, ordered fashion, creating new cells that are exact copies to replace old ones. Certain genes are responsible for telling cells when to divide and when to stop. Other genes and proteins search for problems in DNA and fix them when DNA is not copied correctly. If a problem is found that cannot be fixed, the cell will self-destruct.

If a genetic mutation turns certain genes on or off, then cells can divide at a faster rate without regulation or order. In turn, this allows more and more mutations to accumulate, speeding the unchecked growth of abnormal cells. Eventually, these cells will form a tumor and become cancerous.

Risk Factors for Lung Cancer

It is important to note that while science is good at finding correlations — or apparent relationships — between factors and disease, correlation does not prove the factor causes the disease. Many risk factors for lung cancer have been identified and are being studied for their role in the development of the disease.

Since genetic mutations cause lung cancer, risk factors for lung cancer include anything that can encourage these mutations. It is also important to note that risk factors may vary by the type of lung cancer.

Age

Mutations in DNA are inevitable, and they accumulate with age. In rapidly dividing tissues, researchers estimate that tens of thousands of mutations may accumulate by age 60. However, cancer only develops in a small percentage of people.

For most cases of lung cancer, risk increases with age. Most people are diagnosed with lung cancer at age 65 or older. The average age of diagnosis with lung cancer is around 70 years old. A very small number of people are diagnosed under the age of 45.

Inherited Risk Factors for Lung Cancer

If you have a family history of lung cancer, you are at an increased risk of developing it yourself. Having siblings or parents who had lung cancer may slightly increase your risk, particularly if they were diagnosed at a younger age. It is also possible that you may share exposure to environmental risk factors with them, such as radon or secondhand tobacco smoke. Overall, approximately 8 percent of lung cancer cases are inherited or due to genetic predisposition.

In some cases of lung cancer, people may inherit faulty genes or mutations from their parents. People who inherit mutations found on chromosome 6 are more likely to develop lung cancer, regardless of their smoking status. Usually, these few inherited mutations are not enough alone to cause many lung cancers.

Since cancer is an age-related disease, it is thought that lung cancer in younger people may be due to inherited factors. Some people may inherit faulty DNA-repair mechanisms or a reduced ability to break down carcinogens. All of these factors can contribute to an increased risk of lung cancer.

Sex and Ethnicity

According to the American Lung Association, more men are diagnosed with lung cancer each year, but more women currently live with the disease. Black men are more likely to develop and die from lung cancer compared to any other racial or ethnic group in the U.S.

Those with American Indian/Alaska Native, Asian/Pacific Islander, and Hispanic ethnicity develop lung cancer at lower rates compared to white and Black groups. One mutation in the epidermal growth factor receptor (EGFR) protein is associated with NSCLC adenocarcinoma cases in young Asian women who do not smoke.

Environmental Factors for Lung Cancer

Environmental factors play a large role in the risk of developing lung cancer, because the air you breathe can bring chemicals, pollution, and other irritants into the lungs. Continued exposure to these risk factors may increase your chances of developing lung cancer.

Smoking

Some people who smoke all their lives never develop lung cancer, while some light smokers or nonsmokers may develop it. However, the leading risk factor for lung cancer is smoking, and smoking accounts for around 80 percent of lung cancer deaths. Smoking is a major risk factor for SCLC in particular, which is almost never diagnosed in people who do not smoke.

The method of smoking does not seem to affect the risk of developing lung cancer — cigarettes, cigars, and pipes all contribute to the increased risk. Tobacco smoke contains known carcinogens that damage lung cells and lead to cancer. Therefore, exposure to secondhand smoke may also increase your risk of lung cancer.

Vaping and e-cigarettes are newer forms of smoking, and no studies are available on their long-term effects. However, researchers believe that vaping might not directly cause lung cancer, but vaping raises the risk of developing lung cancer in people who have never smoked before. Inhaling secondhand e-cigarette vapor may also carry risks.

Air Pollution

Air pollution seems to slightly increase the risk of lung cancer. This can be true in cities with high levels of air pollution, especially near busy roads. However, it appears to be far less of a risk compared to smoking. About 5 percent of all lung cancer deaths may be caused by outdoor air pollution.

Radon

Radon is a radioactive gas that naturally forms when uranium found in rocks and soil breaks down. It is invisible and has no smell or taste. According to the Environmental Protection Agency, radon is the second leading cause of lung cancer behind smoking. It is also the leading cause of lung cancer in people who do not smoke.

Radon gas can be found in buildings in nearly any part of the United States, especially in basements. Breathing in radon exposes your lungs to microdoses of radiation, increasing your risk of developing lung cancer.

Asbestos

Asbestos is a fibrous material that was commonly used as insulation in older buildings. If asbestos fibers are inhaled or ingested, they can become permanently trapped in the body. This can cause inflammation and irritate the lungs, eventually leading to cancer.

People who work with asbestos and are exposed to large amounts of it have a greater risk of developing mesothelioma, a type of lung cancer. Asbestos can be found in many workplaces, such as mills, mines, textile plants, and shipyards. Furthermore, the lung cancer risk is much greater in workers exposed to asbestos who also smoke. Most cases of lung cancer occur at least 15 years after the first exposure to asbestos.

Chemicals in the Workplace

Here are some other carcinogens found in some workplaces that can increase the risk of lung cancer:

  • Diesel exhaust
  • Radioactive ores, such as uranium
  • Inhaled chemicals, such as cadmium, arsenic, nickel compounds, coal products, chromium compounds, and mustard gas

Recently, there has been more awareness around protecting workers from harmful chemicals, but any exposure may still put you at risk. Always use protective equipment and limit your exposure to carcinogenic materials whenever possible.

Dietary Supplements

While they may appear beneficial, some vitamins and dietary supplements can actually increase the risk of lung cancer. Two large studies found that beta carotene supplements increased the risk of lung cancer in people who smoke. It is now recommended that people who smoke avoid taking beta carotene supplements.

Radiation Treatment for Cancer

Radiation therapy is a useful cancer treatment that damages cancer cells beyond repair, causing them to stop growing or die. Unfortunately, radiation can also damage healthy cells in the body, increasing the risk of cancer.

People who have had radiation therapy to the chest to treat other types of cancer are at a higher risk for developing lung cancer, especially if they smoke. This might include women who have been treated with chest radiation for breast cancer and people who have been treated for Hodgkin lymphoma. However, women who receive radiation therapy following a lumpectomy on the breast do not appear to have a higher risk of lung cancer.

Can Lung Cancer Be Prevented?

There is no certain way to avoid getting lung cancer, but you can lower your chances. While risk factors such as family history and previous cancer treatment cannot be changed, there are lifestyle and environmental factors that may be within your control.

If you are concerned that you may be at a higher risk for developing lung cancer, here are some measures you can take to lower your risk:

  • Stop smoking and avoid exposure to secondhand smoke.
  • Take precautions when working with carcinogenic chemicals or radiation to limit your exposure. Use protective equipment at all times and follow posted safety procedures.
  • Avoid taking any dietary supplements that may increase your risk of developing lung cancer.
  • Eat a healthy diet with plenty of fresh fruits, vegetables, and whole grains, while limiting your intake of processed meats.

Lung Cancer Condition Guide

References

  1. Germline and Somatic Mutations: What Is the Difference? — ONS Voice
  2. Key Statistics for Lung Cancer — American Cancer Society
  3. If You Have Non-Small Cell Lung Cancer — American Cancer Society
  4. If You Have Small Cell Lung Cancer — American Cancer Society
  5. Familial risk for lung cancer — Oncology Letters
  6. How do genes control the growth and division of cells? — MedlinePlus
  7. Aging and the rise of somatic cancer-associated mutations in normal tissues — PLOS Genetics
  8. What Causes Lung Cancer? — American Cancer Society
  9. Lung Cancer Fact Sheet — American Lung Association
  10. Rate of New Cancers in the United States — Centers for Disease Control and Prevention
  11. Lung Cancer Risk Factors — American Cancer Society
  12. Small Cell Lung Cancer Treatment — National Cancer Institute
  13. How Tobacco Smoke Causes Disease — Centers for Disease Control and Prevention
  14. Does Vaping Cause Lung Cancer? — Moffitt Cancer Center
  15. The Impact of E-Cigarettes on the Lung — American Lung Association
  16. Small Cell Lung Cancer Causes, Risk Factors, and Prevention — American Cancer Society
  17. Asbestos — Asbestos.com
  18. Asbestos and Cancer Risk — American Cancer Society
  19. Healthy Eating — American Institute for Cancer Research

Emily is passionate about immunology, cancer biology, and molecular biology, and understanding how they relate to diseases. Learn more about her here.

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