Lung Cancer in Never-Smokers

Environmental Risk Factors

Secondhand smoke increases lung cancer risk by 24% (RR 1.24, 95% CI 1.13-1.36) in adults living with smokers, with workplace exposure conferring similar risk (RR 1.22, 95% CI 1.13-1.33) 1
A dose-response relationship exists between years of secondhand smoke exposure and lung cancer risk, though this association is weaker than active smoking 1, 2
Eight specific lung carcinogens—arsenic, chromium, asbestos, nickel, cadmium, beryllium, silica, and diesel fumes—confer a mean relative risk of 1.59 for lung cancer development 1, 2, 3
Residential radon exposure demonstrates a linear relationship with lung cancer risk, with meta-analysis showing RR of 1.14 (95% CI 1.0-1.3) 1, 2
Indoor air pollution from coal-fueled stoves and cooking fumes contributes significantly to the high burden of lung cancer in never-smoking women, particularly in Asian countries 4, 5

First-degree relatives of lung cancer patients have an 1.8-fold increased risk (95% CI 1.6-2.0) even after adjusting for age, gender, and smoking habits 1, 2
Patients previously treated with chest irradiation have a 13-fold increased risk for new primary lung cancer, while those treated with alkylating agents have RR of 9.4 1, 2

EGFR mutations occur in approximately 43% of lung cancers in never-smokers compared to only 11% in smokers, with higher prevalence in women, adenocarcinoma histology, and East Asian populations 4
ALK rearrangements are present in 12% of never-smoker lung cancers versus 2% in smokers, representing a therapeutically actionable target 4
Adenocarcinoma accounts for 60-80% of lung cancers in never-smokers, with squamous or adenosquamous representing 10-20% and small cell lung cancer less than 10% 4, 5

Women are disproportionately affected, with 19% of female lung cancers versus 9% of male lung cancers occurring in never-smokers in the United States 4, 5
Women are overrepresented among younger patients, raising questions about gender-specific susceptibility to lung carcinogens 4, 5

Adenocarcinoma accounts for the vast majority of lung cancers in never-smokers, with approximately 19% of female and 9% of male lung cancers in the United States occurring in patients without any tobacco smoking history 6, 7
The proportion of NSCLC patients who are never-smokers has been increasing, particularly in Asian countries, where approximately 500,000 deaths annually are attributed to lung cancer in lifetime never-smokers 8, 9

EGFR mutations occur at significantly higher rates in never-smokers (approximately 10% in Caucasians, higher in East Asians), particularly in the adenocarcinoma subtype, women, and younger patients 10, 11, 12
ALK rearrangements are encountered more frequently in never-smokers with adenocarcinoma (approximately 5% of cases), representing younger patients with the adenocarcinoma subtype 10, 11

EGFR mutation testing should be systematically analyzed in all advanced NSCLC with non-squamous histology, though testing is not recommended in squamous cell carcinoma except in never/former light smokers (<15 packs per year) 10, 11
ALK rearrangement testing should be discussed in non-squamous histology, particularly in never/former light smokers, especially when EGFR and KRAS mutations are absent 10, 11

Environmental exposures, such as radon, asbestos, arsenic, and non-tobacco-related polycyclic aromatic hydrocarbons, are alternative etiologic factors for adenocarcinoma in never-smokers 6, 7
Indoor air pollution, including coal-fueled stoves and cooking fumes, contributes to the high burden in women in certain countries 6, 13, 7
Genetic susceptibility, with heritability estimated at 18%, and identified susceptibility loci including CHRNA3, CHRNA5, TERT, BRCA2, CHECK2, and HLA region, play a role in adenocarcinoma in never-smokers 8, 9