Risk Factors

Researchers have identified several risk factors that increase a person’s risk of developing lung cancer. Some risk factors are controllable, while others are not.

Smoking

Smoking is the major cause of both small cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC). It is estimated that 90% of lung cancer cases are due to active smoking. Male smokers are 23 times more likely to develop lung cancer, and female smokers are 13 more likely to develop lung cancer, compared to people who have never smoked. Smoking contributes to 80% of lung cancer deaths in women and 90% of lung cancer deaths in men.1

Cigarette smoking was modest in the U.S. before World War I. It has been estimated that the average adult smoked fewer than 100 cigarettes per year in 1900. By the mid-1960s, that number rose to approximately 4400 cigarettes per person per year. The number of diagnoses and deaths from lung cancer has increased along with the increase in cigarette smoking. The enormous effect of cigarette smoking far outweighs all other factors leading to lung cancer, and the risk increases with the duration of smoking and the number of cigarettes smoked per day. While there is also an increased risk for lung cancer with other forms of tobacco use, such as cigar and pipe smoking, the risk appears less than with cigarette smoking. The effects of inhaling smoke from marijuana are less studied, but cellular changes indicative of precancerous lesions have been found in smokers of marijuana.2

Secondhand Smoke Exposure

Nonsmokers are 20-30% more likely to develop lung cancer if they are exposed to secondhand smoke at home or at work. Secondhand smoke, also known as environmental tobacco smoke (ETS), includes both the smoke exhaled from a smoker and the smoke from a lighted cigarette, pipe, cigar or hookah. Exposure to secondhand smoke causes approximately 7,330 lung cancer deaths among nonsmokers every year, and there is some evidence suggesting that secondhand smoke may be linked to other cancers in adults and children, including leukemia and brain, bladder, breast cancers.1,3

One study estimated that at least 17% of lung cancers in nonsmokers are attributable to exposure to high levels of secondhand smoke during childhood and adolescence. Nonsmokers exposed to secondhand smoke also have an increased rate of smoke-related problems, such as upper respiratory symptoms and eye irritation.2

Age

As with most cancers, increasing age is an important risk factor for lung cancer. Most lung cancers are diagnosed among people 65-74 years of age.4

Exposure to Radon

Radon is a colorless, tasteless, and odorless gas that is produced by decaying uranium. It occurs naturally in soil and rock, and underground miners have a high risk of exposure to radon. Exposure to radon increases a person’s risk of developing lung cancer, and radon exposure is estimated to be the second-leading cause of lung cancer. It is estimated that approximately 21,000 deaths from lung cancer each year are due to radon exposure. The majority of these deaths are in people who smoke, as the risk of lung cancer is even greater when smokers are exposed to radon.1,2

Exposure to Asbestos & Other Workplace Carcinogens

Carcinogens are substances that are known to cause cancer or increase the risk of developing cancer. Lung cancer can be caused by exposures to carcinogens in the workplace, including asbestos, uranium, and coke (fuel) from iron manufacturing. In addition, the risk of developing lung cancer is even greater for smokers who are exposed to occupational carcinogens. Nonsmokers who are exposed to asbestos are five times more likely to develop lung cancer than those who aren’t exposed to asbestos. Exposure to workplace carcinogens also increases the risk of death from lung cancer.1

Beta-Carotene Supplements in Smokers

Several studies have shown an increased risk of lung cancer among smokers who use high doses of beta-carotene supplements long-term. In normal, healthy, nonsmokers, beta-carotene supplements show a beneficial effect, however, smokers taking beta-carotene have developed more lung cancer tumors than those not taking the supplement.5

Family History of Lung Cancer

There is a genetic component to the development of lung cancer, as the incidence of lung cancer is greater in those with a family history of the disease, with or without smoking or exposure to environmental carcinogens. One meta-analysis that leveraged data from 32 studies demonstrated a 2-fold increased risk for lung cancer in people with a family history of the disease. This increased risk was present for both smokers and nonsmokers.2

Diet

Research suggests that diet is responsible for approximately 30% of all cancers, and many studies suggest that diet plays a contributing role in the risk of lung cancer. In particular, low concentrations of antioxidants, including vitamins A, C, and E, have been associated with the development of lung cancer. A diet rich in fruits and vegetables has been linked to a decreased risk of cancer.2

Radiation Therapy to the Breast or Chest

Radiation therapy is a treatment option for many cancers. One of the potential side effects from radiation therapy is an increased risk of developing secondary cancers (an additional, different cancer from the initial cancer). People who undergo radiation therapy to the breast or chest are at an increased risk of developing lung cancer. This risk is increased in people who smoke.3,6

Air Pollution

Air pollution has long been considered to be a health risk and to increase the risk for lung cancer. The effect of low levels of air pollution exposure over time are difficult to measure, but some studies have shown that people who live in urban areas or cities have a 10-40% increase in lung cancer deaths than those in rural areas.2

Written by: Emily Downward | Last reviewed: January 2017.
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