While a non-small cell lung cancer (NSCLC) diagnosis is often connected to smoking, it’s possible to develop lung cancer even if you’ve never smoked.

Non-small cell lung cancer (NSCLC) is the most common type of lung cancer, accounting for up to 85% of lung cancer diagnoses. It includes cancers such as adenocarcinomas, squamous cell carcinomas, and large cell carcinomas that develop in large, defined epithelial cells of the lungs.

NSCLC is highly associated with smoking, but you can develop this type of lung cancer even if you’ve never smoked. When this happens, it’s natural to wonder “How could this have happened to me?”

Understanding more about the nature of NSCLC can help you find answers to those lingering questions after an unexpected diagnosis.

The causes of lung cancer aren’t always clear, and it’s possible to develop lung cancer even if you have no known risk factors. While smoking is high on the list of contributing factors, the exact causes of all lung cancers are not fully understood, and there are likely contributors that have not yet been discovered.

Genetics, age, environmental pollutant exposure, lung disease, and secondhand smoke exposure are all examples of factors that can contribute to lung cancer even if you’ve never smoked.

Experts aren’t sure why some people develop cancer from smoking while others don’t. It’s believed that, just as you can develop risk factors that increase the likelihood of cancer, you can develop protective factors that reduce the risk.

It’s possible that individual characteristics such as genetics, immunity, physiology, and lifestyle can decrease a person’s chances of developing cancer even if they smoke.

As with risk factors, not all protective factors are yet known.

Most NSCLC diagnoses are directly related to smoking, but other potential causes include:

  • exposure to environmental pollutants such as radon, exhaust, and asbestos
  • chronic lung disease
  • changes in the expression of your genes
  • inherited genetic mutations that predispose you to certain cancers
  • genetic mutations that can occur throughout your life
  • exposure to radiation
  • excessive alcohol consumption
  • inadequate diet and exercise habits
  • chronic stress

For many people, the underlying causes of NSCLC likely stem from a complex combination of multiple known and unknown risk factors.

Genetic testing can analyze your DNA and look for specific genetic mutations or variations that are associated with an increased risk of NSCLC. Common genes that this testing may screen for include:

  • CHEK2
  • ATM
  • TP53
  • BRCA1
  • EGFR
  • APC
  • PALB2
  • EGFR
  • ALK
  • ROS1
  • MET
  • RET
  • BRAF
  • NTRK

A genetic counselor can help you understand the link between your genetics and an NSCLC diagnosis. But remember: Testing positive for a known genetic risk factor is not a guarantee that you’ll develop NSCLC.

About 10% of all new lung cancer diagnoses occur in nonsmokers, according to population-based research from 2021, the most recent year research was completed.

NSCLC is also the most common cancer among nonsmokers, and adenocarcinoma is the most common type of NSCLC diagnosed in this group.

According to the American Cancer Society, the 5-year relative survival rate for NSCLC ranges from 28% to 65%, depending on the cancer stage at diagnosis.

A relative survival rate compares the survival chances of someone with a disease to that of someone without that disease. For example, a 5-year relative survival rate of 65% means that someone with lung cancer is 65% as likely to survive for the next 5 years as someone without lung cancer.

Being a nonsmoker can improve your survival rates in NSCLC.

A comparative study from 2024 found that nonsmokers with a diagnosis of lung cancer, including NSCLC subtypes such as adenocarcinoma, had a 20% lower risk of death than smokers.

Your treatment approach for NSCLC may be different if you’re a nonsmoker.

NSCLC cases not linked to smoking are more likely to have a genetic connection such as an EGFR genetic mutation. This means your NSCLC treatment might involve more targeted therapies than the treatment plan for someone who smokes.

Medications such as Tarceva and Tagrisso have been developed specifically to treat EGFR variants, and other targeted therapies are available to treat different genetic variations.

As a nonsmoker with NSCLC, you might also have fewer underlying conditions to manage, since smoking often contributes to additional health conditions such as chronic obstructive pulmonary disease and asthma. And you won’t have to worry about quitting smoking since you never started in the first place.

NSCLC is the most common lung cancer diagnosis. While it’s typically associated with a history of smoking, you can develop NSCLC even if you’ve never smoked.

Genetics, environmental exposures, underlying health conditions, and still-undiscovered risk factors may all increase your risk of NSCLC.