Lung Cancer Rates in Never-Smokers Are Rising – Causes and What to Know
In this article
🌍 Why Is This in the Spotlight?
Lung cancer is the leading cause of cancer-related deaths worldwide. According to 2022 data, in Canada alone, cancer deaths attributable to lung cancer account for %24,3 , exceeding the combined total from colon, pancreatic and breast cancers. Lung cancer in people who have never smoked may not be increasing in absolute case numbers, but this group represents approximately one-quarter of all lung cancer patients . This makes reassessment of screening programs and public awareness necessary.[1]
🔬 Lung Cancer Types
By cell type, lung cancer is divided into small cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC). Small cell cancers account for %15 of all cases and are almost entirely associated with smoking. NSCLC is classified into adenocarcinoma, squamous cell, large cell and mixed types. Adenocarcinoma is the most common subtype in never-smokers.
- Adenocarcinoma — %40
- Squamous cell carcinoma — %30
- Large cell carcinoma — %10
- Other — %5
- Small cell lung cancer — %15
Note: Percentages are an example distribution and may vary between epidemiological series.
📊 Historical Data: 1990–2013 United States Study
In 2017, the Journal of the National Cancer Institute (JNCI) published a study presenting detailed analyses of 10.593 non-small cell lung cancer (NSCLC) and 1.510 small cell lung cancer (SCLC) patients. This large dataset is based on three major cancer centers in the United States and all their patient records from 1990–2013. Rather than absolute case numbers, the research assessed changes over time in patient proportions by smoking status .
Results showed that among NSCLC patients, the proportion of never-smokers in the 1990s was around %10 and in 2011–2013 rose to %16. Sex-based analysis found the increase reached %17,5 in women and %6,9 in men. This shows a more pronounced increase in female never-smoker NSCLC patients.
The study also found no significant change in the never-smoker proportion in small cell lung cancer or the NSCLC squamous cell subtype. The findings are important because they show changes in proportions within the patient pool rather than an absolute case increase and suggest nonsmoking risk factors have become more visible.[2][3]
🇨🇦 2025 Canadian Update
Current data and expert views published in Canada in 2025 highlight the tendency toward late-stage diagnosis in lung cancer and limitations of screening programs:
- Never-smoker patients: In Canada, lung cancer diagnoses are estimated to include %20–25 in people who have never smoked.[1]
- Late-stage diagnosis: Approximately %50 of patients at stage III or IV are diagnosed; this rate exceeds those for breast, colon and prostate cancers.[4]
- Lack of screening: Current low-dose CT screening protocols rely only on older age and a high pack-year smoking history , leaving never-smokers almost entirely outside their scope.[5]
- Symptom awareness problem: Warning symptoms such as persistent cough or breathlessness are often disregarded by both patients and physicians when there is no smoking history, contributing to delayed diagnosis .[5]
- Molecular medicine and survival: With broad molecular testing panels and immunotherapies, in advanced lung cancer 5-year survival has doubled over the last 15 years. Experts report that with personalized treatment according to tumor biology , some advanced-stage patients live 10 years or longer.[6]
This current picture clearly shows that lung cancer risk in nonsmokers is not rare, screening criteria need review and personalized treatments are becoming more important.
🧭 Possible Reasons for the Increasing Never-Smoker Share
- Relative (proportion) effect: Declining smoking and smoking-related lung cancer cases → in the total group , the proportion of never-smokers appears to increase.
- Changes in diagnosis and classification: High-resolution CT, PET-CT and 2011 IASLC classification updates (such as reclassification of bronchioloalveolar patterns) increased adenocarcinoma detection.
- Access to molecular diagnosis: With wider NGS availability, EGFR, ALK, ROS1, RET, METex14 and similar drivers are detected more often; some of these subtypes occur more frequently in never-smokers.
- Environmental exposures: Radon (especially in insulated enclosed environments), PM2.5 and air pollutants such as diesel exhaust, asbestos/silica and other occupational factors; the burden varies by country.
- Passive smoking: Chronic exposure to secondhand tobacco smoke at home and work.
- Indoor sources: In some regions, unvented/cooking smoke, heaters, solid fuels and volatile organic compounds.
- Demographic-cultural dynamics: Urbanization, longer lifespans and differences in healthcare access → affect the likelihood and timing of diagnosis.
- Hormonal and biological factors: Certain adenocarcinoma subtypes particularly seen in women and possible estrogen receptor signaling are being discussed.
- Previous treatments: To the chest area, radiotherapy (for example after lymphoma/breast cancer) is a rare but known risk.
- Screening and care pathways: LDCT criteria focused on smoking history → in never-smokers, late-stage diagnosis and reporting increase.
- Registry and awareness effect: Improved awareness and registry systems allow more accurate coding of never-smoker status.
Note: These factors have different weights across countries; rather than one cause, the picture is multifactorial .
🧬 Molecular Subtypes and the Treatment Revolution
The greatest leap in lung cancer over the last 15 years came through integrating molecular diagnostic technologies and immunotherapies into clinical practice. Next-generation sequencing (NGS) panels routinely detect many driver mutations and fusions, including EGFR, ALK, ROS1, RET, METex14, KRAS G12C . This knowledge has enabled personalized targeted treatment options for patients.
Particularly in EGFR-mutated or ALK-positive adenocarcinomas, oral tyrosine kinase inhibitors (TKIs) have enabled long-term disease control even in metastatic disease. In addition, PD-1/PD-L1 and CTLA-4 axis-targeting immunotherapies dramatically prolong survival alone or with chemotherapy.
According to clinical assessments in Canada, 5-year survival has doubled over the last 15 years . Widening nationwide NGS access during the COVID-19 pandemic accelerated this success. Today, in some molecular subtypes, survival of 10 years or longer is possible even in metastatic disease. These advances have led lung cancer to be viewed as a “group of diseases” with dozens of subtypes rather than one disease.
📌 Conclusions and Recommendations
- Lung cancer in never-smokers is not rare; one-quarter of all patients belong to this group.
- Late-stage diagnosis rates are high; cough and breathlessness should be taken seriously even without a smoking history.
- Expanding screening criteria and awareness efforts is critical.
- Molecular testing should be recommended at diagnosis for all patients.
Sources
2. Pelosof L, Ahn C, Gao A, et al. Proportion of Never-Smoker NSCLC Patients at Three Diverse Institutions. J Natl Cancer Inst. 2017.
3. Canadian Partnership Against Cancer. Stage at Diagnosis Data. 2022.
4. Moffatt J. Ontario Lung Screening Program, 2025 yorumları.
5. Drozdogan.com. Sigara dışı akciğer kanseri nedenleri.
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