For decades, lung cancer has been closely associated with smoking — and for good reason. Smoking remains the leading cause of lung cancer worldwide.

But researchers are increasingly recognizing another pattern: an estimated 10–20% of lung cancers are now diagnosed in people who have never smoked.

Scientists now consider lung cancer in never-smokers (LCINS) to be a distinct disease, with different biology, different genetic drivers, and potentially different treatment approaches.

A Different Kind of Lung Cancer

Once considered a disease of older adults who smoke, the rise of lung cancer in nonsmokers and young adults is an alarming trend.

LCINS is now recognized as a distinct disease entity that is biologically different from lung cancer caused by smoking.

Unlike smoking-related lung cancers, which accumulate thousands of DNA changes from years of tobacco exposure, LCINS is often driven by a smaller number of specific gene mutations that fuel tumor growth.

Approximately 10–20% of lung cancers are now in nonsmokers, and two-thirds of LCINS cases occur in women, more frequently in women of Asian descent. Researchers have found that certain cancer-driving mutations occur more frequently in these populations, which may help explain some of the differences in risk.

Learn More About Lung Cancer

Why Are Cases Increasing?

Researchers don’t yet know exactly why lung cancer in never-smokers is becoming more common. The increase likely reflects a combination of factors rather than a single cause. Environmental exposures such as radon, secondhand smoke, and air pollution appear to play an important role, while inherited genetic susceptibility and acquired gene mutations may increase risk in some people.

Researchers are also improving their understanding of LCINS as its own disease, leading to better recognition and diagnosis. Ongoing research continues to investigate how these factors work together to drive cancer development.

Which Types of Lung Cancer Affect Nonsmokers?

There are two major types of lung cancer:

Non-small cell lung cancer (NSCLC) accounts for about 85% of cases. Adenocarcinoma — the most common subtype of NSCLC — is also the type most often diagnosed in people who have never smoked.

Small cell lung cancer (SCLC) is less common and strongly associated with cigarette smoking.

What Increases the Risk?

Exposure to secondhand smoke, radon, and air pollution are considered the greatest risk factors for developing lung cancer in never smokers.

Secondhand Smoke

Contains about 7,000 chemicals, including about 70 that are known to cause cancer. No amount of secondhand smoke exposure is considered safe, and even brief exposure can damage the cells lining the lungs over time.

Radon

Radon is the leading cause of lung cancer among people who have never smoked. Radon is a naturally occurring radioactive gas produced by the radioactive decay of uranium and can be found at high concentrations in indoor environments. It has no color, smell, or taste, making it difficult to identify.

Radon causes cancer by depositing radioactive particles in the cells lining our airways. These particles can damage our DNA, potentially causing lung cancer. In outdoor settings, radon levels are quickly diluted; however, it can be found in higher concentrations in indoor settings with poor ventilation, such as caves, mines, and water treatment facilities. In work and residential buildings, radon levels can vary significantly, which is why testing is important.

Fortunately, radon levels in homes can be measured with inexpensive test kits, and elevated levels can often be reduced through home mitigation systems.

Air Pollution

Especially fine particulate matter PM2.5 can increase cancer risk by traveling deep into the respiratory tract, causing chronic inflammation and creating conditions that allow DNA damage to accumulate. Studies have shown a strong association between air pollution exposure and new genetic mutations in lung tumors in nonsmokers.

The World Health Organization recommends PM2.5 concentrations remain below 5 µg/m³. While the average in the U.S. at any given time is around 7 µg/m³, places like India have an average of nearly 50 µg/m³, with some cities seeing well over 100 µg/m3, highlighting a global disparity in air pollution exposure.

Researchers are also increasingly concerned about the growing frequency and intensity of wildfires, which produce hazardous smoke containing high levels of fine particulate matter. For example, in the summer of 2026, Canadian wildfires drove pollution values over 175 µg/m³ in the New York City metro area and across the U.S.

*New York City, July 2026. Getty Images*

Why Diagnosis Can Be Challenging

Over 70% of lung cancer cases are diagnosed in advanced stages because early-stage tumors often have no obvious symptoms. Additionally, screening guidelines only recommend lung cancer screening for adults over 50 years of age with a history of heavy smoking.

Because younger adults and people who have never smoked aren’t traditionally considered high risk, symptoms may initially be mistaken for asthma, allergies, or other common respiratory illnesses, potentially delaying diagnosis.

Early signs of lung cancer can include:

persistent cough
coughing up blood
chest pain
shortness of breath
unexplained weight loss
persistent fatigue
recurrent pneumonia or bronchitis
hoarseness

Having one or more of these symptoms does not necessarily mean you have lung cancer. However, if they persist for several weeks or worsen over time — especially without a clear explanation — it’s important to discuss them with a healthcare provider.

Treatment Is Becoming More Personalized

Since LCINS is recognized as its own disease category, treatment varies from lung cancer in smokers and depends heavily on the cancer stage and genetic profile:

Targeted therapy: These medications are designed to attack specific gene mutations that allow cancer cells to grow, which can be common in lung cancers that develop in people who have never smoked.
Surgery: Suitable for early-stage tumors that haven’t spread to remove the cancer.
Chemotherapy and radiation: Used to shrink tumors or eliminate lingering cancer cells following surgery.
Immunotherapy: Teaches your immune system to identify and attack cancer cells. While typically less effective in lung cancer in nonsmokers compared to smokers, it’s increasingly being used alongside other therapies.

Lung cancers caused by smoking often carry many DNA mutations, making them easier for the immune system to recognize once the “brakes” on immune cells are released by checkpoint inhibitors. Because LCINS tumors usually have fewer mutations, immunotherapy alone may be less effective for some patients. Researchers are actively studying combination approaches that may improve responses.

Looking Ahead

Although lung cancer in never-smokers remains relatively uncommon compared with smoking-related lung cancer, its rising incidence highlights how much remains to be understood. Researchers around the world are working to uncover why these cancers develop, identify people at greatest risk, and develop more effective, personalized treatments.

While no one can eliminate every risk factor, understanding environmental exposures, recognizing persistent symptoms, and seeking medical evaluation when something doesn’t feel right can make an important difference. As scientists continue to unravel the biology of LCINS, each new discovery brings us closer to earlier detection, more personalized treatments, and better outcomes for patients.