Smoking is one of the biggest risk factors for lung cancer. However, lung cancer can still occur in a person who has never smoked. While it is rarer, lung cancer can develop following exposure to radon, secondhand smoke, air pollution, and other factors.

According to the American Lung Association, as many as 20% of people in the United States who die of lung cancer every year are nonsmokers. The “nonsmoker” classification includes people who have never smoked and those who have smoked fewer than 100 cigarettes in their lifetime.

In this article, we explore lung cancer in nonsmokers, including causes, symptoms, and treatments.

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Although there are some similarities between lung cancer in smokers and nonsmokers, there are also a few differences, such as the following:

Subtype

The most common type of lung cancer diagnosed in nonsmokers is adenocarcinoma. Research estimates that 93% of lung cancers in nonsmokers are adenocarcinoma. This type of cancer involves cells that line the small airways of the lungs.

Nonsmokers may also develop squamous cell cancer or mesothelioma, but these types are rarer. Research also notes that certain genetic mutations are more common in lung cancer among nonsmokers.

Evidence also suggests that lung cancers in nonsmokers tend to grow slower. However, while they are less likely to spread, they can still recur, even following successful surgery.

Sex

Worldwide, up to 20% of males with lung cancer are nonsmokers. But over 50% of females with lung cancer are nonsmokers.

Researchers are still unsure why, but current evidence suggests it may relate to genetics, certain hormones, or higher rates of exposure to secondhand smoke.

Outlook

Although there are conflicting studies, some research indicates that the outlook is better among nonsmokers compared to former smokers or current smokers.

Possibly increasing rates

Overall, lung cancer rates have appeared to decline in the last several years. But some studies indicate that there may be an increase in lung cancer among nonsmokers.

For example, a 2017 study involving 12,103 people with lung cancer in three U.S. hospitals notes an increase. From 1990–1995, 8% of the lung cancer patients were nonsmokers. But the number of patients with lung cancer that were nonsmokers from 2011–2013 increased to 14%.

There are several possible causes of lung cancer in nonsmokers, including:

Environmental factors

Various environmental factors may contribute to the development of lung cancer in nonsmokers, such as:

Carcinogens

Carcinogens are substances that may cause cancer. Possible lung cancer carcinogens include:

  • asbestos
  • uranium
  • heavy metals

Genetics

Genetics likely play a significant role in the development of lung cancer in people that do not smoke.

A 2015 study notes that 73% of nonsmokers with lung cancer had a notable mutation or alteration. In particular, alterations in the genes EGFR, ALK, KRAS, and RET occur more frequently in nonsmokers with lung cancer.

According to the Centers for Disease Control and Prevention (CDC), the symptoms of lung cancer are similar in smokers and nonsmokers. Symptoms may include:

  • a cough that does not get better
  • coughing up blood
  • shortness of breath
  • fatigue
  • hoarseness
  • wheezing
  • chest pain

Smoking is a well-known risk factor for lung cancer. As potential causes in nonsmokers are not as well known, people may not seek immediate treatment and instead attribute symptoms to allergies or other respiratory conditions, such as asthma.

Treatment for lung cancer in nonsmokers depends on the stage of the disease. Typically, treatment may include:

  • Surgery: Usually, for early-stage lung cancer, surgery is part of the treatment plan. Different surgical approaches include removing only the tumor, part of the lung, or the entire lung.
  • Chemotherapy: Chemotherapy includes a combination of cancer-fighting medications administered through a vein or taken by mouth.
  • Radiation therapy: Radiation therapy involves directing high-energy rays to destroy cancer cells.
  • Targeted therapies: This type of medication targets specific proteins that affect how cancer cells divide, grow, and spread.

A 2020 study notes that lung cancer in nonsmokers is likely to respond differently to targeted therapies. This study notes the distinct attributes and hallmarks of lung cancer in nonsmokers and suggests they may help enable a path of precision medicine to manage nonsmoking lung cancer.

Not smoking is one of the best ways to reduce the risk of lung cancer. But nonsmokers can also take additional steps to decrease their chances of lung cancer. Changes that may help to reduce the risk include:

  • eating a healthy diet, such as one high in vegetables and fruits
  • avoiding secondhand smoke
  • decreasing exposure to pollution as much as possible
  • following health and safety guidelines to limit exposure to carcinogens at work and using appropriate protective equipment
  • having the home tested for radon
  • knowing family history to be aware of an increased genetic risk for lung cancer

Studies on the difference in lung cancer outlook between smokers and nonsmokers are conflicting.

While some research does show better outcomes in nonsmokers, it is not definitive. It is also important to understand that the outlook varies based on factors such as the stage at diagnosis, age, and response to treatment.

There are two main types of lung cancer: small cell and non-small cell lung cancer (NSCLC). Adenocarcinoma is the most common form of lung cancer in nonsmokers and is a type of NSCLC.

According to the American Cancer Society, the 5-year survival rates for people with all types of NSCLC range from 63% with localized disease to 7% for people with lung cancer classified as distant, meaning the cancer has spread. The overall 5-year survival rate is 25%.

Up to 20% of cases of lung cancer may occur in people that are nonsmokers. Nonsmoking lung cancer is more common in females, and adenocarcinoma is the most common type of lung cancer in nonsmokers.

Causes of lung cancer in nonsmokers may include exposure to secondhand smoke, air pollution, and carcinogens. Genetics may also play a role in the development of lung cancer in nonsmokers.

Symptoms and treatments for lung cancer in nonsmokers are typically similar to those in smokers. The outlook varies based on stage, but some studies indicate that nonsmokers have a slightly better outlook than smokers.