Why Is Lung Cancer Increasing in Non-Smokers?

The reason why lung cancer is increasing in non-smokers and never-smokers isn't entirely clear. Research suggests that some people may have a genetic predisposition for lung cancer that makes them vulnerable to environmental carcinogens (like air pollution, radon, asbestos, and secondhand smoke) that other people may be more resistant to. Young females and Asian people who have never smoked are especially vulnerable.

Because lung cancer is largely regarded as a "smoker's disease," non-smokers may miss the signs of the disease until it is advanced and has begun to spread. This is why it is important to recognize the signs of lung cancer whether you smoke heavily or have never touched a cigarette in your life.

How Common Is Lung Cancer in Never-Smokers?

In recent decades, the rate of lung cancer among never-smokers (as opposed to non-smokers who may have smoked at one time) has risen dramatically.

Although tobacco smoking accounts for the vast majority of lung cancer cases, lung cancer among never-smokers is today the fifth most common cause of cancer-related deaths worldwide, according to a 2023 study published in the National Review of Clinical Oncology.

The rise in lung cancer cases among never-smokers comes at a time when cigarette smoking has declined, reaching an all-time low of 11.5% in 2021 (down by 42% from 1964 when the U.S. Surgeon General first linked cigarettes to cancer).

In 2023, over 20,000 lung cancer deaths were reported among never-smokers in the U.S., accounting for just under one-fifth of all cancer deaths for that year.

Statistically speaking, this makes lung cancer among never-smokers the eighth leading cause of cancer-related deaths in the U.S. Globally, it is the fifth most common cause of cancer-related deaths.

All told, between 10% to 15% of lung cancer cases in the United States occur in never-smokers, with rates expected to increase.

Who Is at Risk of Lung Cancer Among Never-Smokers?

Studies have shown that two groups of never-smokers are especially vulnerable to lung cancer: females and Asian people.

Statistically, female never-smokers are more than twice as likely as male never-smokers to get lung cancer. In total, around two-thirds of all cases involve women. This is despite the fact that U.S. men represent over 80% of lung cancer cases overall.

Of these women, over 55% are Asian, followed by Hispanic females who account for more than 30% of cases.

As with smokers, lung cancer among never-smokers tends to affect people over 60, albeit slightly earlier than either smokers or former smokers.

Never-smokers also differ in that they almost exclusively develop a type of cancer called lung adenocarcinoma. Adenocarcinoma is a typically slow-growing non-small cell lung cancer (NSCLC) that affects the lining of the small airways (called bronchioles).

Genetics and Risk of Lung Cancer in Never-Smokers

Although lung cancer is strongly associated with cigarette smoking, only around 15% of smokers end up getting the disease. This suggests that other factors contribute to the risk of cancer, both in smokers and non-smokers.

While environmental factors play a large role in this—causing inflammation and DNA damage that causes cells to mutate—certain genetic factors may make it easier for these changes to occur.

This is evidenced by the fact that lung cancer in smokers has different genetic mutations than lung cancer in never-smokers. These include the EGFR, Ki-67, and HTERT mutations commonly seen in smokers, and p-AKT and p27 mutations common in never-smokers.

There also appear to be differences in how cancer-causing mutations develop.

In most cases, cancerous mutations develop in lungs that have been genetically altered by years of smoking (referred to as acquired mutations). As these mutations mount, one atop the next, cells can begin to transform and become malignant (cancerous).

With never-smokers, many of these mutations may already be present at birth. As such, fewer acquired mutations may be needed for cells to turn malignant.

This may explain in part why never-smokers tend to get lung cancer at an earlier age than smokers.

Possible Causes for Lung Cancer in Never-Smokers

As with other types of cancer, lung cancer may develop for no apparent reason. In theory, cancerous mutations may develop spontaneously in someone who is genetically predisposed to the disease.

However, lung cancer is generally thought to involve some sort of environmental "trigger" that turns an overwise benign growth cancerous.

The American Cancer Society notes three possible causes among never-smokers:

Radon Gas

Radon gas is an invisible, odorless gas that can accumulate in homes built to soil containing even modest deposits of uranium. Exposure to radon gas is considered one of the leading causes of cancer among never-smokers, accounting for around 21,000 lung cancer deaths in the United States each year.

Secondhand Smoke

Secondhand smoke is the tobacco smoke you inhale from another person’s cigarette or cigar. It is estimated that over 7,000 lung cancer deaths occur in the U.S. due to secondhand smoke.

It is also possible to get exposed to thirdhand smoke. This is the invisible film of nicotine and other chemicals left on surfaces, clothing, and furniture that you can touch and introduce into your body. Children who crawl on contaminated floors and carpets are especially vulnerable.

Occupational Exposure

There are many carcinogenic (cancer-causing) agents used in industrial and manufacturing industries that can be inhaled and increase the risk of lung cancer. These include solvents, toxins, pesticides, and heavy metals like:

• Air pollution
• Arsenic
• Asbestos
• Beryllium
• Carbon dioxide
• Coal smoke and soot
• Chromium
• Cobalt
• Diesel fumes
• Dioxin
• Formaldehyde
• Ionizing radiation
• Nickel
• Phenoxyacetic acid
• Vinyl chloride

People who work in construction (including masonry, painting, and sand-blasting), coal/coke plants, or ceramics, rubber, or glass manufacturing are especially vulnerable. Traffic police and long-distance drivers are at high risk of exposure to air pollution and car fumes.

Ionizing radiation exposure can occur with fracking, nuclear power plants, and uranium processing facilities, but stringent safety measures usually minimize the risk.

Signs of Lung Cancer in Never-Smokers

The early signs of lung adenocarcinoma are often vague and non-specific and easily missed by someone who doesn't smoke. Even if treatment is sought, X-rays can often miss the cancer because it will look less like a solid mass and more like specks of sand inside the tiny bronchioles.

To this end, you should be aware of the signs and symptoms of lung cancer, particularly if you have a family history of the disease.

These include:

• A cough that doesn’t go away or gets worse over time
• Chest pain or discomfort
• Fatigue
• Shortness of breath
• Wheezing
• Hoarseness
• Difficulty swallowing
• Loss of appetite
• Recurrent lung infections, including pneumonia
• Unexplained weight loss
• Swelling of the face and/or neck
  

Other tests like sputum cytology or endobronchial ultrasound can be performed if imaging studies are negative or inconclusive.

How to Prevent Lung Cancer If You Don't Smoke

Lung cancer can affect never-smokers as well as smokers and former smokers. To reduce your risk and the risk of others in your family who don't smoke:

• Never allow smoking in your home or cars.
• Avoid public places where smoking is allowed.
• If traveling, only book non-smoking rooms or use a nicotine detection test like KnowSmoke to check for signs of thirdhand smoke residue.
• Always follow occupational safety guidelines in industries when exposure to carcinogens is common. The guidelines are largely regulated by the Occupational Safety and Health Administration (OSHA).
• Get a radon home test available at most major hardware stores. If radon mitigation is needed, contact your state radon program for authorized providers in your area. They can also advise you if there are federal or state programs to help reduce the cost of mitigation.

Summary

Between 10% and 15% of lung cancer cases in the United States involve people who never smoked. Of the roughly 125,000 people who die each year from lung cancer, never-smokers account for around 20,000 of these deaths. Females and Asian people are at greatest risk.

The cause of lung cancer in never-smokers is poorly understood, but genetics is thought to play a part. Among the most common causes in never-smokers are radon gas in the home, secondhand smoke, and occupational exposure to carcinogens like diesel fume, asbestos, and vinyl chloride.