Rising Lung Cancer Rates in Never Smokers: Understanding the Risks and New Approaches to Detection and Prevention

Lung cancer remains the leading cause of cancer-related death globally, but a concerning trend is emerging: an increase in diagnoses among individuals who have never smoked. This phenomenon, known as lung cancer in never smokers (LCINS), requires a distinct understanding of its causes, characteristics, and potential strategies for early detection and prevention, as traditional models focused on smoking history are often inadequate for this population.

An Emerging Burden and Distinct Biology

Although the absolute incidence of LCINS remains lower than that of smoking-related lung cancer, it represents a growing percentage of cases worldwide. Historically overshadowed by smoking-associated disease, LCINS is now recognized as a biologically and clinically distinct entity. Research indicates that LCINS tumors often exhibit a lower mutational burden, a higher prevalence of actionable driver mutations, and potentially reduced responsiveness to immune checkpoint inhibitors compared to tumors in smokers.

LCINS is more frequently observed in women and individuals of Asian descent, particularly among women who have never smoked. The reasons for these disparities are still under investigation. A significant challenge in LCINS is that many patients are diagnosed at an advanced or metastatic stage, often due to not meeting the criteria for traditional lung cancer screening.

Genetic Susceptibility and Clonal Hematopoiesis

Identifying individuals at elevated risk of LCINS, despite never smoking, is a complex undertaking. However, emerging research highlights the role of both inherited and acquired biological predispositions. Germline variants – genetic mutations inherited from parents – in genes like EGFR, TP53, ATM, and those within the APOBEC3 family have been linked to increased lung cancer risk. Specific mutations, such as EGFR p.Thr790Met (T790M), can significantly elevate lifetime risk and potentially lead to the development of multiple lung lesions at a younger age.

Population-specific genetic factors too play a role. For example, the APOBEC3A/B germline deletion has been shown to substantially increase the risk of certain lung cancers in specific ethnic groups. These findings suggest that genetic screening, particularly in high-prevalence populations, could inform risk-adapted surveillance strategies.

Clonal hematopoiesis of indeterminate potential (CHIP) is another emerging risk factor. CHIP involves somatic mutations (acquired during life, not inherited) in hematopoietic stem cells, often affecting genes like DNMT3A, TET2, and ASXL1. Individuals with high variant allele fractions associated with CHIP may have a higher risk of solid tumors, including lung cancer, independent of smoking status. The mechanism behind this link may involve chronic inflammation and elevated interleukin-1β (IL-1β) signaling.

Environmental Exposures and the Exposome

Beyond genetic factors, the “exposome” – the cumulative measure of environmental exposures throughout a person’s life – is crucial in the development of LCINS. Radon exposure, particularly in poorly ventilated indoor spaces and certain geographic regions, is a well-established carcinogen. While occupational exposure in miners has been historically recognized, residential radon remains a public health concern.

Exposure to secondhand smoke increases lung cancer risk in never smokers by approximately 20–25%. Interestingly, tumors in these individuals may not consistently exhibit the mutational signatures typically associated with direct smoking, suggesting that indirect tobacco exposure may interact with other biological processes, such as those involving the APOBEC family of enzymes.

Air pollution, particularly fine particulate matter (PM2.5), is a known carcinogen strongly associated with lung cancer incidence. High PM2.5 exposure correlates with a greater mutation burden, TP53 mutations, telomere shortening, and inflammation within the lung. Similar to CHIP, pollution-induced inflammation, particularly IL-1β-mediated signaling, appears to contribute to tumorigenesis.

Screening, Early Detection, and Prevention Strategies

Early detection is critical for improving outcomes in lung cancer. Low-dose computed tomography (LDCT) screening has demonstrated a 20% reduction in lung cancer mortality among heavy smokers. However, applying LDCT to never smokers is controversial due to the difficulty in defining high-risk individuals without a smoking history, concerns about false positives and overdiagnosis, and cost-effectiveness considerations.

A clinical trial in Taiwan identified an elevated risk among never smokers with a first-degree family history of lung cancer, leading to an expansion of national screening criteria. Preliminary data suggest that LDCT may be effective in selected high-risk never-smoker subgroups, such as Asian women with a familial predisposition. However, larger randomized trials are needed to assess mortality benefit and cost-effectiveness in broader never-smoker populations.

Multi-cancer early detection blood tests based on circulating tumor DNA are also under investigation, but their sensitivity for detecting very early lung cancer remains limited.

Prevention strategies are also evolving. Targeted therapies, immunotherapies, and cancer vaccines are being explored for the treatment of premalignant or early-stage disease. Vaccines targeting clonal neoantigens, as well as peptide-based approaches, are being evaluated for their preventive potential. Given the frequent presence of actionable, immunogenic driver mutations in LCINS tumors, this population may be particularly well-suited for vaccine-based interception strategies.

Conclusion

LCINS is an increasingly important global health problem that demands distinct diagnostic, screening, and therapeutic approaches. Integrating genetic susceptibility, clonal hematopoiesis, family history, and environmental exposures into comprehensive risk models may enable more precise screening and prevention strategies. Continued research into the biological underpinnings of LCINS is essential for developing tailored interception strategies to reduce mortality in this underrecognized and growing patient population.