7 Causes of Lung Cancer in Non-Smokers

It's not just smokers who are at risk for lung cancer—about 20% of lung tumors develop in non-smokers. However, there are enough differences between the groups to almost consider them two different diseases, says Vincent Lam, M.D., a lung cancer specialist at the University of Texas MD Anderson Cancer Center in Houston. People with lung cancer who have never smoked tend to be younger than smokers (and former smokers) who get the disease, and are more likely to be women.

The tumors, too, are distinct, and tend to have different genetic mutations. About half of tumors in people who have never smoked have mutations that can be targeted by newer drugs. This may help explain why non-smokers with lung cancer tend to live longer than current and former smokers with the disease.

Researchers are still testing out all the different factors that can contribute to lung cancer in people who’ve never smoked. Some cases may never be explained, but here’s what is known so far.

RELATED: The Stages of Lung Cancer, Explained

The Environmental Protection Agency identifies radon as the main cause of lung cancer after smoking. Radon gas, a byproduct of uranium breaking down, can be found in the air around us and is generally harmless. The danger comes when this naturally occurring radioactive gas gets trapped and concentrated, as can happen in mines and in the lower floors of some homes. Even then, you need to be exposed for a long time to get sick.

Because radon can’t be seen and has no odor, the only way to know if it’s there is to test for it. Officials recommend that all homes be tested with an easy-to-use kit. If levels are too high, they can be reduced. While radon can be found in any area, some states tend to have higher levels than others. (Check this EPA Map of Radon Zones to see if you live in an area that's more radon-prone.)

RELATED: Former USA Hockey Star Rachael Malmberg, 33, Says Radon Gas Caused Her Stage 4 Lung Cancer

Some 15% to 35% of lung cancers in non-smokers may be caused by secondhand smoke, also referred to as passive smoke. There are two different types. Sidestream smoke (the more toxic of the two) is when a non-smoker inhales smoke from the lighted end of a person’s cigarette or cigar. Mainstream smoke is when a non-smoker inhales the exhaled smoke from the smoker.

Fortunately, great strides have been made in reducing exposure to secondhand smoke. “That’s why we banned smoking in restaurants, at workplaces, in a park,” says Ahmedin Jemal, PhD, vice president of Surveillance and Health Services Research at the American Cancer Society in Atlanta.

Some groups are more susceptible to getting lung cancer from secondhand smoke, including people exposed to it in childhood and those living in poverty.

RELATED: Yes, There's Such a Thing as Third-Hand Smoke. Here's What You Need to Know

Asbestos refers to a group of minerals found in many building materials as well as car parts and ships. Because the link to lung cancer is well known, asbestos is used much less often today than it was in years past. You’re most at risk for developing lung cancer from asbestos if you work in a high-risk industry such as construction, especially if the job involves removing asbestos.

“Its contribution [to lung cancer] is quite small and has probably decreased over time,” says Jemal.

RELATED: This Woman Thought She Had Pneumonia—but It Turned Out to Be Stage 4 Lung Cancer

Pollution from vehicle exhaust, power plants, wood stoves, and other sources contain tiny particles that can also contribute to lung cancer. The Clean Air Act has greatly reduced air pollution—and lung cancer caused by air pollution—in the U.S., but it is still a major problem in other parts of the world, like China.

In fact, in 2013 the International Agency for Research on Cancer (IARC) declared outdoor air a potential carcinogen because of the link to lung and bladder cancer.

RELATED: What Is Lung Cancer’s Survival Rate?

People who’ve had radiation treatment to their chest (usually for another type of cancer), also have a higher risk for lung cancer, even if they’ve never smoked.

“Women who’ve had previous radiation for breast cancer or younger patients who’ve had Hodgkins lymphoma with chest radiation—that does increase your risk for lung cancer, but that’s not common,” says Dr. Lam.

RELATED: This Woman Posted a Photo of Her Curved Nail on Facebook—and Had 'No Idea' It Was a Sign of Cancer

In addition to genetic differences between lung cancer tumors in people who smoke or have smoked versus those who never have, researchers are also finding genetic differences in the people themselves. These can be inherited (which is why lung cancer sometimes runs in families) or acquired during your lifetime.

RELATED: Lung Cancer and COPD Turned This Person’s Lungs Completely Black

According to the World Health Organization, around 3 billion people around the world cook and heat their home with solid fuels (wood and coal) or cook over open flames. This type of cooking paired with poor ventilation leads to high levels of indoor air pollution which can contribute to lung cancer.

Women and children are more likely to be affected by this indoor pollution due to their proximity to the cooking fire, and time spent in the household. Lower income populations across the world, like in rural China, are often where these high levels of indoor air pollution occur.

RELATED: The Lung Cancer Symptoms You Need to Know, Even If You've Never Smoked

If you’ve never smoked, the best thing you can do to avoid lung cancer is stay away from people who are smoking, test for radon at home, and make sure work safety standards are in place if you work in a high-risk industry.

CT screenings are now recommended for lung cancer screenings in people who are at high risk (long-term smokers over 55, in addition to other risk factors), but for other people, the risks of screening generally outweigh the benefits. For example, the test exposes people to a dose of radiation and some people end up having a false positive—the test indicates cancer, but more testing reveals that the patient does not actually have cancer.

RELATED: These Foods and Eating Habits May Increase Your Risk of Lung Cancer

There’s also evidence that a healthy diet with fruits and vegetables may help ward off lung cancer. “Eating healthy and being healthy—these things that may increase your risk of lung cancer when you’re not doing [them]” can help prevent cancer, says Ticiana Leal, M.D., assistant professor of medicine at the  University of Wisconsin Carbone Cancer Center in Madison, Wis.

To get our top stories delivered to your inbox, sign up for the Healthy Living newsletter