What causes lung cancer in nonsmokers? 

Public health campaigns and surgeon general warnings have long focused on smoking as a leading cause of lung cancer. But not everyone diagnosed with lung cancer has a history of smoking.

In fact, about 15% to 20% of people with lung cancer have never smoked cigarettes, says Ravi Manglani, M.D., a pulmonary and critical care physician with Sutter.

While smoking remains the biggest risk factor, it’s not the only one. Genetics, secondhand smoke, radon gas and environmental exposures can also increase the risk of lung cancer in nonsmokers

What causes lung cancer?

Smoking cigarettes accounts for about 80% to 85% of lung cancer diagnoses. But other factors can contribute to lung cancer, even in people who have never smoked.

Genetics may play a role for some patients. Certain inherited gene mutations can increase the likelihood of developing lung cancer.

“There are particular genes that are passed down within families that portend to a higher rate of development of these cancers,” Manglani says.

Family history is another important consideration.

“People who have had a first-degree relative, say a parent or sibling, who had lung cancer, that increases your risk by about one and half times,” Manglani says. The risk appears to be especially high among siblings, he adds.

Secondhand smoke exposure can also increase lung cancer risk over time.

“The person who is actually smoking the cigarette is getting a filtered version of carcinogens,” Manglani explains. “The sidestream smoke that’s coming off the edge of the cigarette is unfiltered.”

Some studies estimate that long-term exposure to secondhand smoke increases lung cancer risk by about 20% to 30%.

Radon gas is another major risk factor and is considered the second leading cause of lung cancer after smoking. Radon is a naturally occurring radioactive gas that can enter homes through cracks and openings in the foundation.

“It’s a naturally ocurring breakdown product of uranium,” Manglani says. “And it seeps up from the soil and into the homes of people, unbeknownst to them.”

Because radon is colorless and odorless, many people don’t realize they have elevated levels in their homes. Testing kits are widely available, and radon mitigation systems can help reduce exposure if radon levels are high.

Other environmental exposures — including air pollution, asbestos and certain workplace chemicals — may also increase lung cancer risk. 

Lung cancer symptoms

Lung cancer symptoms can vary, but common warning signs include fatigue and unexplained weight loss, a persistent or worsening cough, coughing up blood, and shortness of breath.

Unfortunately, lung cancer often doesn’t cause symptoms in its earliest stages. By the time symptoms appear, the disease may already be in an advanced stage.

The overall five-year lung cancer survival rate is about 30%, according to the American Cancer Society. But survival rates improve significantly when cancer is caught early, before it has spread.

That’s why screening is so important, Manglani says. Yet only about 16% of people in the United States who are eligible for lung cancer screening actually undergo yearly screening. 

Lung cancer screenings

The United States Preventive Services Task Force (USPSTF) recommends annual lung cancer screening with low-dose CT scans for certain high-risk patients.

In general, screening is recommended for adults ages 50 to 80 who have at least a 20-pack-year smoking history and who currently smoke or quit within the past 15 years.

Current screening guidelines don’t include the many nonsmoking-related risk factors, such as family history or radon exposure. However, the National Comprehensive Cancer Network (NCCN) recommends that people with a family history of lung cancer talk with their healthcare provider about their risk.

In some cases, genetic counseling or testing may also be appropriate. “If you have concerns about your risk, it’s worth having a conversation with your doctor,” Manglani says. 

Lung cancer treatment

Lung cancer treatment depends on the type of cancer and how advanced it is when diagnosed. Treatment options may include surgery, chemotherapy, radiation therapy, immunotherapy and targeted therapy.

Targeted therapies can be especially helpful for some patients whose lung cancer is caused by specific genetic mutations. These medications are designed to target cancer cells with certain genetic characteristics while limiting damage to healthy cells.

“The silver lining in that cloud,” Manglani says, “is that those non-smoking patients with this genetic cause of lung cancer typically have these particular genes that we can target for treating the lung cancer.”

As with many cancers, early detection remains one of the most important factors in improving outcomes. If you have concerns about lung cancer risk or whether you may qualify for screening, talk with your healthcare provider.