August 22, 2017

What Is Lung Cancer: Risk Factors, Genetics and Types


Cancer is a disease in which cells in the body grow out of control. When cancer starts in the lungs, it is called lung cancer. Lung cancer, therefore, is the uncontrolled growth of abnormal cells in one or both lungs. These abnormal cells do not carry out the functions of normal lung cells and do not develop into healthy lung tissue. As they grow, the abnormal cells can form tumors and interfere with the functioning of the lung, which provides oxygen to the body via the blood.

Risk factors for lung cancer

Lung cancer is the leading cause of cancer death and the second most diagnosed cancer in both men and women in the United States. In 2011, 14% of all cancer diagnoses and 27% of all cancer deaths in the USA were due to lung cancer. After increasing for decades, lung cancer rates are now decreasing nationally in many countries, as fewer people smoke cigarettes.

Research has found several risk factors that may increase your chances of getting lung cancer. Cigarette smoking is the number one cause of lung cancer. Lung cancer also can be caused by using other types of tobacco (such as pipes or cigars), breathing secondhand smoke, being exposed to substances such as asbestos or radon at home or work, and having a family history of lung cancer.

1). Smoking

Cigarette smoking is the number one risk factor for lung cancer. In the United States, cigarette smoking is linked to about 80% to 90% of lung cancers. Using other tobacco products such as cigars or pipes also increases the risk for lung cancer. Tobacco smoke is a toxic mix of more than 7,000 chemicals. Many are poisons. At least 70 are known to cause cancer in people or animals.

People who smoke cigarettes are 15 to 30 times more likely to get lung cancer or die from lung cancer than people who do not smoke. Even smoking a few cigarettes a day or smoking occasionally increases the risk of lung cancer. The more years a person smokes and the more cigarettes smoked each day, the more risk goes up.

People who quit smoking have a lower risk of lung cancer than if they had continued to smoke, but their risk is higher than the risk for people who never smoked. Quitting smoking at any age can lower the risk of lung cancer.

Cigarette smoking can cause cancer almost anywhere in the body. Cigarette smoking causes cancer of the mouth and throat, esophagus, stomach, colon, rectum, liver, pancreas, voicebox (larynx), trachea, bronchus, kidney and renal pelvis, urinary bladder, and cervix, and causes acute myeloid leukemia.

2). Secondhand Smoke

Smoke from other people’s cigarettes, pipes, or cigars (secondhand smoke) also causes lung cancer. When a person breathes in secondhand smoke, it is like he or she is smoking. In the United States, two out of five adults who don’t smoke and half of children are exposed to secondhand smoke, and about 7,300 people who never smoked die from lung cancer due to secondhand smoke every year.

3). Radon

Radon is a naturally occurring gas that comes from rocks and dirt and can get trapped in houses and buildings. It cannot be seen, tasted, or smelled. According to the U.S. Environmental Protection Agency (EPA), radon causes about 20,000 cases of lung cancer each year, making it the second leading cause of lung cancer. Nearly one out of every 15 homes in the U.S. is thought to have high radon levels. The EPA recommends testing homes for radon and using proven ways to lower high radon levels.

4). Other Substances

Examples of substances found at some workplaces that increase risk include asbestos, arsenic, diesel exhaust, and some forms of silica and chromium. For many of these substances, the risk of getting lung cancer is even higher for those who smoke.

4). Personal or Family History of Lung Cancer

If you are a lung cancer survivor, there is a risk that you may develop another lung cancer, especially if you smoke. Your risk of lung cancer may be higher if your parents, brothers or sisters, or children have had lung cancer. This could be true because they also smoke, or they live or work in the same place where they are exposed to radon and other substances that can cause lung cancer.

6). Radiation Therapy to the Chest

Cancer survivors who had radiation therapy to the chest are at higher risk of lung cancer.

7). Diet

Scientists are studying many different foods and dietary supplements to see whether they change the risk of getting lung cancer. There is much we still need to know. We do know if smokers who take beta-carotene supplements have increased risk of lung cancer. For more information, visit the CDC's Lung Cancer Prevention.

Also, arsenic in drinking water (primarily from private wells) can increase the risk of lung cancer. For more information, visit the EPA’s Arsenic in Drinking Water.

The Genetic Basis of Lung Cancer

All cells in the body contain the genetic material called deoxyribonucleic acid (DNA). Every time a mature cell divides into two new cells, its DNA is exactly duplicated. The cells are copies of the original cell, identical in every way. In this way our bodies continually replenish themselves. Old cells die off and the next generation replaces them.

A cancer begins with an error, or mutation, in a cell’s DNA. DNA mutations can be caused by the normal aging process or through environmental factors, such as cigarette smoke, breathing in asbestos fibers, and to exposure to radon gas.

Researchers have found that it takes a series of mutations to create a lung cancer cell. Before becoming fully cancerous, cells can be precancerous, in that they have some mutations but still function normally as lung cells. When a cell with a genetic mutation divides, it passes along its abnormal genes to the two new cells, which then divide into four cells with errors in their DNA and so on. With each new mutation, the lung tissue cell becomes more mutated and may not be as effective in carrying out its function as a lung cell. At a later stage of disease, some cells may travel away from the original tumor and start growing in other parts of the body. This process is called metastasis and the new distant sites are referred to as metastases.

Types of lung cancer

1). Small Cell Versus Non-Small Cell

Lung cancers usually are grouped into two main types called small cell and non-small cell. These types of lung cancer grow differently and are treated differently. Non-small cell lung cancer (NSCLC) is more common than small cell lung cancer (SCLC). More about these types in the lung cancer treatment section.

2). Primary Versus Secondary

Primary lung cancer starts in the lungs. The cancer cells are abnormal lung cells. Sometimes, people will have cancer travel from another part of their body or metastasize to their lungs. This is called secondary lung cancer because the lungs are a secondary site compared to the original primary location of the cancer. So, for example, breast cancer cells which have traveled to the lung are not lung cancer but rather metastatic breast cancer, and will require treatment prescribed for breast cancer rather than lung cancer.

1). Centers for Disease Control: Lung Cancer - Basic information. Accessed 22.08.2017. Available here: https://www.cdc.gov/cancer/lung/basic_info/
2). Lung Cancer 101: What is lung cancer?. Accessed 22.08.2017. Available here: https://www.lungcancer.org/find_information/publications/163-lung_cancer_101/265-what_is_lung_cancer

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