Lung Cancer in Non-Smokers: Why a “Smoker’s Disease” Is Increasingly Diagnosed in People Who Never Smoked

Why this matters

For most of the twentieth century, lung cancer was framed — accurately — as the signature disease of tobacco. Smoking still causes the majority of lung cancers worldwide and remains, by far, the single most important modifiable risk factor. But as smoking rates have fallen across high-income countries, a parallel story has come into clearer view: a sizeable and apparently growing share of lung cancers is occurring in people who have never smoked.

Recent peer-reviewed work, including a 2025 comprehensive review in JAMA^[1] and a landmark global genomic analysis published in Nature^[2], now estimate that 15–25% of all lung cancers worldwide occur in never-smokers, with the proportion approaching 50% in parts of East Asia. If lung cancer in never-smokers (LCINS) were classified as its own disease, it would rank among the most common causes of cancer mortality in the United States (Samet et al., Clinical Cancer Research, 2009^[3]; Murphy et al., JAMA, 2025^[1]).

This article walks through what the current evidence does — and does not — tell us about who is being diagnosed, why incidence appears to be rising, and what general, population-level prevention looks like.

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What “never-smoker” actually means

In the research literature, a never-smoker is consistently defined as a person who has smoked fewer than 100 cigarettes in their lifetime (Murphy et al., JAMA, 2025^[1]). Studies sometimes use slightly different thresholds, but this is the most widely accepted definition and the one used in the major epidemiologic datasets cited below.

Two abbreviations appear in the literature: LCINS (Lung Cancer In Never-Smokers) and LCNS (Lung Cancer in Never-Smokers). They mean the same thing.

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A growing share of cases

The most consistently reported trend is not that lung cancer overall is rising — in the United States, age-adjusted lung cancer incidence has actually fallen substantially as smoking rates declined from about 23% in 2000 to about 11.5% in 2021 (Murphy et al., JAMA, 2025^[1]; Siegel et al., CA: A Cancer Journal for Clinicians, 2025^[4]).

The trend is that the share of remaining lung cancers occurring in never-smokers has grown. A retrospective US cohort study of roughly 10,000 patients across three hospital networks (Pelosof and colleagues, JNCI) found that the proportion of lung cancer occurring in non-smokers rose from 8% in 1990 to 14.9% in 2013 (Pelosof et al., JNCI, 2017^[5]).

There is also evidence that absolute incidence is climbing in some populations, not just the proportional share. In a pooled analysis of Finnish cohorts cited in the JAMA 2025 review, the absolute incidence of lung cancer in never-smokers nearly doubled from about 6.9 per 100,000 person-years in 1972 to 12.9 per 100,000 person-years in 2015 (Murphy et al., JAMA, 2025^[1]).

How much of this reflects true biological increase versus better detection — for example, from more chest CT imaging done for unrelated reasons — is still debated, particularly in East Asian populations where indolent ground-glass nodules are commonly picked up on screening (Murphy et al., JAMA, 2025^[1]). The most cautious read of the data is that both are likely contributing.

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Who is being diagnosed

Lung cancer in never-smokers does not affect all groups equally. Several patterns are now well documented.

Women are disproportionately affected

Among people diagnosed with lung cancer, about 19% of women are never-smokers compared with about 9% of men (Murphy et al., JAMA, 2025^[1]). In Taiwan, up to 83% of never-smoker lung cancer cases occur in women (Murphy et al., JAMA, 2025^[1]).

Geography matters a great deal

LCINS is most common in East Asia. Up to 50% of lung cancers in East Asian populations occur in never-smokers (JTO Clinical and Research Reports, 2025^[6]), compared with roughly 10–15% historically in Western Europe.

Ethnicity within the US

US data show meaningful disparities. The age-adjusted incidence of LCINS among Asian American women between 2000 and 2013 was 17.5 per 100,000 person-years, compared with 10.1 per 100,000 in non-Hispanic White women (Murphy et al., JAMA, 2025^[1]).

Age

Never-smokers are diagnosed at a median age of 67 years, slightly younger than the 70 years typical of former or current smokers (Murphy et al., JAMA, 2025^[1]). A subset of LCINS — particularly in East Asian women — is diagnosed under age 50 (Wang et al., Journal of Translational Medicine, 2023^[7]).

Histology

About 60–80% of LCINS are adenocarcinomas, compared with roughly 40% among current or former smokers (Murphy et al., JAMA, 2025^[1]). Adenocarcinomas tend to develop in the peripheral lung and often appear on imaging as ground-glass or subsolid nodules — a pattern very different from the central, endobronchial tumors classically associated with smoking.

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What may be driving the trend

There is no single cause of lung cancer in never-smokers. The evidence points to a combination of environmental exposures, inherited and acquired genetic susceptibility, and biological promoters of cancer growth in lung tissue that already harbors low-level mutations. The 2025 JAMA review summarized the best current estimates of how much of the LCINS burden each factor explains.

These percentages overlap (a person can have several risk factors at once) and they are not additive. The “targetable genetic alterations” bar represents underlying molecular susceptibility within tumors, not an exogenous carcinogen people are exposed to.

The major risk factors, in approximate order of strength of evidence:

Radon

Radon is the leading environmental cause of lung cancer in non-smokers in the United States. It is a naturally occurring, odorless, radioactive gas produced by uranium decay in soil and rock. It seeps into homes and decays into radioactive particles that lodge in lung tissue and damage DNA through alpha-particle radiation.

According to the US Environmental Protection Agency^[8], radon is responsible for approximately 21,000 lung cancer deaths annually in the United States, of which about 2,900 occur in never-smokers. The International Agency for Research on Cancer classifies radon as a Group 1 (definite) human carcinogen, and large European pooled analyses have found roughly an 8–16% increase in lung cancer risk per 100 Bq/m³ increase in residential radon (Bhopal & Scott, Expert Review of Respiratory Medicine, 2019^[9]).

This makes radon the most actionable known modifiable risk factor for LCINS in the US: residential test kits cost roughly $15–$25, and mitigation systems (sub-slab depressurization) cost on average $800–$2,500 and can reduce indoor radon by up to 99% (EPA, Health Risk of Radon^[8]).

Outdoor air pollution (PM2.5)

In 2013, the International Agency for Research on Cancer classified outdoor air pollution, and fine particulate matter (PM2.5) specifically, as a Group 1 human carcinogen for lung cancer (IARC Press Release No. 221, 2013^[10]).

The mechanistic case strengthened substantially in 2023, when a landmark paper from Charles Swanton’s group, published in Nature^[11], proposed that PM2.5 does not act primarily as a classical mutagen. Instead, it appears to be a promoter: PM2.5 inhaled into the lung triggers inflammation (via the cytokine IL-1β released from lung macrophages), which then expands populations of cells already carrying low-level, pre-existing EGFR mutations — mutations the authors found in roughly 18% of normal lung tissue from healthy adults (Hill et al., Nature, 2023^[11]).

The 2025 Sherlock-Lung study, which analyzed 871 LCINS genomes from patients in 28 countries, added a complementary finding: patients from higher-pollution regions had more TP53 mutations, shorter telomeres, a 3.9-fold increase in a tobacco-associated mutational signature (SBS4), and a 76% increase in a clock-like signature (SBS5) — a clear dose-response between PM2.5 and somatic mutation burden (Díaz-Gay et al., Nature, 2025^[2]).

Together these papers suggest air pollution likely acts as both a promoter and, at higher exposures, a mutagen.

Secondhand smoke

Secondhand smoke (SHS) is a long-established cause of lung cancer in non-smokers. Pooled analyses estimate roughly a 20–30% increase in lung cancer risk from spousal or sustained workplace SHS exposure, and SHS is estimated to account for about 15% of LCINS cases (Samet et al., Clinical Cancer Research, 2009^[3]; Murphy et al., JAMA, 2025^[1]). A 2024 systematic review and meta-analysis in the European Respiratory Review confirmed the association in contemporary data (European Respiratory Review, 2024^[12]).

Despite substantial progress through smoke-free workplace and public-space policies, SHS exposure remains common, particularly in lower-income households and in multi-unit housing.

Occupational exposures

Workplace exposures are estimated to contribute roughly 13% of LCINS cases (Murphy et al., JAMA, 2025^[1]). Established occupational lung carcinogens include asbestos, crystalline silica, arsenic, hexavalent chromium, nickel, cadmium, beryllium, coal tar, and diesel exhaust. Risks are often additive or synergistic when more than one exposure is present (Environmental Health Perspectives, 2024^[13]).

5. Indoor air pollution and cooking fumes

This factor is comparatively small at the global level (about 4% of LCINS cases in the JAMA estimate) but substantially more important in East Asian women (Murphy et al., JAMA, 2025^[1]). High-heat wok cooking with oils that reach smoke point, performed in poorly ventilated kitchens, produces polycyclic aromatic hydrocarbons and aldehydes. Meta-analyses report odds ratios in the range of 1.5–2.5 for high cooking-fume exposure in women, with a dose-response relationship (Sustainability, 2026 indoor air meta-analysis^[14]).

In lower-income settings, indoor combustion of biomass, coal, and other solid fuels for heating and cooking contributes meaningfully to lung cancer risk and is one of the largest drivers of LCINS globally.

6. Genetic susceptibility and family history

Having a first-degree relative with lung cancer is associated with roughly a 2-fold increased risk of lung cancer, even among never-smokers, and contributes to an estimated 26% of LCINS risk in the JAMA review (Murphy et al., JAMA, 2025^[1]).

A small number of families inherit specific cancer-predisposing variants — including the germline EGFR T790M mutation, which defines a rare hereditary early-onset lung adenocarcinoma syndrome (Journal of Thoracic Oncology, 2014^[15]). Genome-wide association studies have also identified susceptibility loci at 5p15.33 (TERT/CLPTM1L), 6p21, and 15q25, with some loci specific to East Asian populations.

Prior lung disease

Tuberculosis, COPD, chronic bronchitis, and pulmonary fibrosis are each associated with elevated lung cancer risk in never-smokers, with TB conferring an odds ratio of roughly 2.4 in pooled analyses (JCO meta-analysis, 2024^[16]). One mechanism under investigation is transcriptional remodeling of lung epithelium by pulmonary macrophages following chronic inflammation (Journal of Experimental Medicine, 2025^[17]).

Open questions

Several proposed contributors remain uncertain, and the honest answer is that the evidence does not yet support firm conclusions:

• HPV. Some studies, mostly from Taiwan, have detected HPV-16 and HPV-18 DNA in lung tumors, but methodological concerns and inconsistent Western data leave a causal role unestablished (Wang et al., Journal of Translational Medicine, 2023^[7]).
• E-cigarettes and vaping. A 2025 systematic review concluded that current evidence is insufficient to establish a causal link with lung cancer (Tobacco Induced Diseases, 2025^[18]). Cancer typically requires decades of latency, and widespread e-cigarette use is still relatively recent.
• Estrogen and reproductive factors in women — biologically plausible, but epidemiologic findings are inconsistent (Cancer, 2023^[19]).
• Aristolochic acid (from certain herbal medicines) — the 2025 Sherlock-Lung study found its characteristic mutational signature almost exclusively in Taiwanese patients, a novel finding requiring replication (Díaz-Gay et al., Nature, 2025^[2]).

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A biologically distinct disease

The seminal 2007 review by Sun, Schiller, and Gazdar in Nature Reviews Cancer called lung cancer in never-smokers “a different disease,” and the genomic data of the past two decades have validated that framing (Sun et al., Nature Reviews Cancer, 2007^[20]).

Compared with smoking-related tumors, LCINS tumors have a lower mutation burden (typically 0–3 mutations per megabase versus 0–30 in smokers) but a substantially higher rate of targetable driver mutations — single oncogenic alterations that act as the dominant biological engine of the tumor and can be matched with a precision drug (Murphy et al., JAMA, 2025^[1]).

EGFR mutations are about four times more common in never-smoker non-small cell lung cancers than in smoker tumors (43% versus 11%), and the EGFR mutation rate climbs further — to roughly 40–60% — in East Asian never-smoker patients (Murphy et al., JAMA, 2025^[1]; Díaz-Gay et al., Nature, 2025^[2]). ALK rearrangements are roughly six times more common (12% versus 2%). ROS1, RET, HER2, and MET alterations are all enriched in never-smoker tumors as well.

This pattern has two important clinical consequences:

1. Targeted therapy is often highly effective. Third-generation EGFR tyrosine kinase inhibitors such as osimertinib have produced median overall survival exceeding 38 months in EGFR-mutant non-small cell lung cancer, and ALK inhibitors such as alectinib have produced progression-free survival exceeding 34 months (Murphy et al., JAMA, 2025^[1]).
2. Immunotherapy alone tends to work less well. Because LCINS tumors carry few mutations, they present fewer “neoantigens” for the immune system to recognize, which is why immune checkpoint inhibitors as a single agent are generally less effective in this population.

The practical takeaway frequently emphasized in current expert reviews is that comprehensive molecular profiling (next-generation sequencing) at diagnosis is essential for any patient with non-small cell lung cancer, regardless of smoking history — because identifying a targetable mutation can change treatment substantially. This is a discussion to have with the treating oncologist.

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The screening gap

Current US lung cancer screening guidelines are built almost entirely around smoking history. The 2021 US Preventive Services Task Force^[21] recommendation supports annual low-dose CT screening for adults aged 50–80 with a ≥20 pack-year smoking history who currently smoke or have quit within the past 15 years. The American Cancer Society’s 2024 update widened those criteria — but kept the smoking-history requirement in place (Medical Science Monitor, 2025 editorial^[22]).

Never-smokers — by design — fall entirely outside these criteria. The International Association for the Study of Lung Cancer has noted that current eligibility criteria can miss over 50% of lung cancers when never-smokers are excluded (Kerpel-Fronius et al., Journal of Thoracic Oncology, 2021^[23]).

The most informative real-world experiment in screening never-smokers has come from Taiwan. The TALENT study prospectively screened 12,011 asymptomatic Taiwanese never-smokers aged 55–75 with at least one risk factor (a first-degree relative with lung cancer, passive smoking, or cooking without ventilation) using low-dose CT, and detected lung cancers predominantly at early, treatable stages (Chang et al., Lancet Respiratory Medicine, 2023^[24]). In 2022, Taiwan launched the world’s first national LDCT screening program for non-smokers with a family history of lung cancer — biennial screening for women aged 45–74 and men aged 50–74 (Murphy et al., JAMA, 2025^[1]).

Comparable programs have not been adopted in the US, UK, Europe, or Australia. Concerns about overdiagnosis — particularly of indolent adenocarcinoma in situ in Asian women — are legitimate and an active area of research. Whether high-risk never-smokers in Western populations should be offered screening is one of the most important open policy questions in lung cancer prevention today.

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What prevention can look like

Most LCINS risk factors are at least partly modifiable at the population or household level. The following are general, evidence-informed concepts — not personal medical advice.

Radon.

• The EPA recommends that every home in the US be tested for radon.
• Testing is inexpensive (~$15–$25 for a DIY test kit) and widely available through state radon programs and hardware stores.
• The EPA action level is 4 pCi/L; mitigation is also worth considering between 2 and 4 pCi/L.
• Sub-slab depressurization systems typically reduce indoor radon by up to 99%.

Outdoor air quality.

• Where feasible, reducing time outdoors during high-AQI days, using well-fitted N95/KN95 respirators during severe pollution events, and supporting policies that lower PM2.5 emissions are all reasonable population-level approaches.
• HEPA air purifiers can reduce indoor PM2.5 by 50–80% and may be particularly relevant in high-pollution urban areas.

Indoor air and cooking fumes.

• Using a vented range hood, opening windows, and avoiding cooking oils past their smoke point are practical steps with biologic plausibility, especially in homes that do high-heat or wok-based cooking.

Secondhand smoke.

• Smoke-free homes and vehicles, particularly when children or non-smoking adults are present, are the most direct intervention.
• Multi-unit-housing smoke-free policies meaningfully reduce involuntary exposure.

Occupational exposures.

• Workplace respiratory protection programs, adherence to OSHA permissible exposure limits, and engineering controls (ventilation, dust suppression, substitution of safer materials) remain the core of occupational lung cancer prevention.

Family history awareness.

• Knowing whether first-degree relatives have had lung cancer is information clinicians use when discussing personal risk and the (currently limited) options for surveillance in non-smokers.

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Questions you may want to discuss with your clinician

These are general prompts for an informed conversation, not instructions:

• “Has my home ever been tested for radon? Is testing something you’d recommend in our area?”
• “Given my family history of lung cancer, are there any current surveillance options that would apply to me?”
• “What is the typical air quality in our region, and are there practical steps that might lower my long-term exposure?”
• “I have a history of [TB / COPD / chronic bronchitis / prior chest radiation]. Does that affect how you think about my long-term lung health?”
• “If I or a family member were ever diagnosed with non-small cell lung cancer, what would comprehensive molecular testing involve, and why does it matter?”

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Key takeaways

• Lung cancer in never-smokers accounts for an estimated 15–25% of all lung cancers globally, and up to 50% in parts of East Asia (Murphy et al., JAMA, 2025^[1]; Díaz-Gay et al., Nature, 2025^[2]).
• The proportion is rising, and absolute incidence appears to be rising in at least some populations, though detection improvements likely contribute as well.
• Women, East Asian populations, and people with a first-degree family history are disproportionately affected.
• Radon is the leading environmental cause of LCINS in the US, and it is the most actionable modifiable risk factor for many households (EPA^[8]).
• Outdoor air pollution (PM2.5) has both epidemiologic and mechanistic evidence supporting causation, including a landmark 2023 Nature paper on IL-1β-driven tumor promotion (Hill et al., Nature, 2023^[11]).
• Secondhand smoke, occupational carcinogens, indoor cooking and biomass fumes, and genetic susceptibility all contribute meaningfully.
• LCINS is biologically distinct, with substantially higher rates of targetable driver mutations (EGFR, ALK, ROS1, RET, HER2, MET) and a strong rationale for comprehensive molecular profiling at diagnosis.
• Current screening guidelines exclude never-smokers. Whether to extend screening to high-risk never-smokers is one of the most important open questions in lung cancer prevention.

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A note on uncertainty

The picture of LCINS we have today is far clearer than it was a decade ago, but several questions remain genuinely open: how much of the rising incidence is biology versus detection; whether HPV, vaping, or hormonal factors play a meaningful role; and whether screening can be safely extended to never-smokers without causing net harm from overdiagnosis. Future analyses from the Sherlock-Lung consortium, ongoing screening trials, and population-level air quality interventions will likely sharpen the picture over the next 5–10 years.

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Why this matters

For most of the twentieth century, lung cancer was framed — accurately — as the signature disease of tobacco. Smoking still causes the majority of lung cancers worldwide and remains, by far, the single most important modifiable risk factor. But as smoking rates have fallen across high-income countries, a parallel story has come into clearer view: a sizeable and apparently growing share of lung cancers is occurring in people who have never smoked.

Recent peer-reviewed work, including a 2025 comprehensive review in JAMA^[1] and a landmark global genomic analysis published in Nature^[2], now estimate that 15–25% of all lung cancers worldwide occur in never-smokers, with the proportion approaching 50% in parts of East Asia. If lung cancer in never-smokers (LCINS) were classified as its own disease, it would rank among the most common causes of cancer mortality in the United States (Samet et al., Clinical Cancer Research, 2009^[3]; Murphy et al., JAMA, 2025^[1]).

This article walks through what the current evidence does — and does not — tell us about who is being diagnosed, why incidence appears to be rising, and what general, population-level prevention looks like.

---

What “never-smoker” actually means

In the research literature, a never-smoker is consistently defined as a person who has smoked fewer than 100 cigarettes in their lifetime (Murphy et al., JAMA, 2025^[1]). Studies sometimes use slightly different thresholds, but this is the most widely accepted definition and the one used in the major epidemiologic datasets cited below.

Two abbreviations appear in the literature: LCINS (Lung Cancer In Never-Smokers) and LCNS (Lung Cancer in Never-Smokers). They mean the same thing.

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A growing share of cases

The most consistently reported trend is not that lung cancer overall is rising — in the United States, age-adjusted lung cancer incidence has actually fallen substantially as smoking rates declined from about 23% in 2000 to about 11.5% in 2021 (Murphy et al., JAMA, 2025^[1]; Siegel et al., CA: A Cancer Journal for Clinicians, 2025^[4]).

The trend is that the share of remaining lung cancers occurring in never-smokers has grown. A retrospective US cohort study of roughly 10,000 patients across three hospital networks (Pelosof and colleagues, JNCI) found that the proportion of lung cancer occurring in non-smokers rose from 8% in 1990 to 14.9% in 2013 (Pelosof et al., JNCI, 2017^[5]).

There is also evidence that absolute incidence is climbing in some populations, not just the proportional share. In a pooled analysis of Finnish cohorts cited in the JAMA 2025 review, the absolute incidence of lung cancer in never-smokers nearly doubled from about 6.9 per 100,000 person-years in 1972 to 12.9 per 100,000 person-years in 2015 (Murphy et al., JAMA, 2025^[1]).

How much of this reflects true biological increase versus better detection — for example, from more chest CT imaging done for unrelated reasons — is still debated, particularly in East Asian populations where indolent ground-glass nodules are commonly picked up on screening (Murphy et al., JAMA, 2025^[1]). The most cautious read of the data is that both are likely contributing.

---

Who is being diagnosed

Lung cancer in never-smokers does not affect all groups equally. Several patterns are now well documented.

Women are disproportionately affected

Among people diagnosed with lung cancer, about 19% of women are never-smokers compared with about 9% of men (Murphy et al., JAMA, 2025^[1]). In Taiwan, up to 83% of never-smoker lung cancer cases occur in women (Murphy et al., JAMA, 2025^[1]).

Geography matters a great deal

LCINS is most common in East Asia. Up to 50% of lung cancers in East Asian populations occur in never-smokers (JTO Clinical and Research Reports, 2025^[6]), compared with roughly 10–15% historically in Western Europe.

Ethnicity within the US

US data show meaningful disparities. The age-adjusted incidence of LCINS among Asian American women between 2000 and 2013 was 17.5 per 100,000 person-years, compared with 10.1 per 100,000 in non-Hispanic White women (Murphy et al., JAMA, 2025^[1]).

Age

Never-smokers are diagnosed at a median age of 67 years, slightly younger than the 70 years typical of former or current smokers (Murphy et al., JAMA, 2025^[1]). A subset of LCINS — particularly in East Asian women — is diagnosed under age 50 (Wang et al., Journal of Translational Medicine, 2023^[7]).

Histology

About 60–80% of LCINS are adenocarcinomas, compared with roughly 40% among current or former smokers (Murphy et al., JAMA, 2025^[1]). Adenocarcinomas tend to develop in the peripheral lung and often appear on imaging as ground-glass or subsolid nodules — a pattern very different from the central, endobronchial tumors classically associated with smoking.

---

What may be driving the trend

There is no single cause of lung cancer in never-smokers. The evidence points to a combination of environmental exposures, inherited and acquired genetic susceptibility, and biological promoters of cancer growth in lung tissue that already harbors low-level mutations. The 2025 JAMA review summarized the best current estimates of how much of the LCINS burden each factor explains.

These percentages overlap (a person can have several risk factors at once) and they are not additive. The “targetable genetic alterations” bar represents underlying molecular susceptibility within tumors, not an exogenous carcinogen people are exposed to.

The major risk factors, in approximate order of strength of evidence:

Radon

Radon is the leading environmental cause of lung cancer in non-smokers in the United States. It is a naturally occurring, odorless, radioactive gas produced by uranium decay in soil and rock. It seeps into homes and decays into radioactive particles that lodge in lung tissue and damage DNA through alpha-particle radiation.

According to the US Environmental Protection Agency^[8], radon is responsible for approximately 21,000 lung cancer deaths annually in the United States, of which about 2,900 occur in never-smokers. The International Agency for Research on Cancer classifies radon as a Group 1 (definite) human carcinogen, and large European pooled analyses have found roughly an 8–16% increase in lung cancer risk per 100 Bq/m³ increase in residential radon (Bhopal & Scott, Expert Review of Respiratory Medicine, 2019^[9]).

This makes radon the most actionable known modifiable risk factor for LCINS in the US: residential test kits cost roughly $15–$25, and mitigation systems (sub-slab depressurization) cost on average $800–$2,500 and can reduce indoor radon by up to 99% (EPA, Health Risk of Radon^[8]).

Outdoor air pollution (PM2.5)

In 2013, the International Agency for Research on Cancer classified outdoor air pollution, and fine particulate matter (PM2.5) specifically, as a Group 1 human carcinogen for lung cancer (IARC Press Release No. 221, 2013^[10]).

The mechanistic case strengthened substantially in 2023, when a landmark paper from Charles Swanton’s group, published in Nature^[11], proposed that PM2.5 does not act primarily as a classical mutagen. Instead, it appears to be a promoter: PM2.5 inhaled into the lung triggers inflammation (via the cytokine IL-1β released from lung macrophages), which then expands populations of cells already carrying low-level, pre-existing EGFR mutations — mutations the authors found in roughly 18% of normal lung tissue from healthy adults (Hill et al., Nature, 2023^[11]).

The 2025 Sherlock-Lung study, which analyzed 871 LCINS genomes from patients in 28 countries, added a complementary finding: patients from higher-pollution regions had more TP53 mutations, shorter telomeres, a 3.9-fold increase in a tobacco-associated mutational signature (SBS4), and a 76% increase in a clock-like signature (SBS5) — a clear dose-response between PM2.5 and somatic mutation burden (Díaz-Gay et al., Nature, 2025^[2]).

Together these papers suggest air pollution likely acts as both a promoter and, at higher exposures, a mutagen.

Secondhand smoke

Secondhand smoke (SHS) is a long-established cause of lung cancer in non-smokers. Pooled analyses estimate roughly a 20–30% increase in lung cancer risk from spousal or sustained workplace SHS exposure, and SHS is estimated to account for about 15% of LCINS cases (Samet et al., Clinical Cancer Research, 2009^[3]; Murphy et al., JAMA, 2025^[1]). A 2024 systematic review and meta-analysis in the European Respiratory Review confirmed the association in contemporary data (European Respiratory Review, 2024^[12]).

Despite substantial progress through smoke-free workplace and public-space policies, SHS exposure remains common, particularly in lower-income households and in multi-unit housing.

Occupational exposures

Workplace exposures are estimated to contribute roughly 13% of LCINS cases (Murphy et al., JAMA, 2025^[1]). Established occupational lung carcinogens include asbestos, crystalline silica, arsenic, hexavalent chromium, nickel, cadmium, beryllium, coal tar, and diesel exhaust. Risks are often additive or synergistic when more than one exposure is present (Environmental Health Perspectives, 2024^[13]).

5. Indoor air pollution and cooking fumes

This factor is comparatively small at the global level (about 4% of LCINS cases in the JAMA estimate) but substantially more important in East Asian women (Murphy et al., JAMA, 2025^[1]). High-heat wok cooking with oils that reach smoke point, performed in poorly ventilated kitchens, produces polycyclic aromatic hydrocarbons and aldehydes. Meta-analyses report odds ratios in the range of 1.5–2.5 for high cooking-fume exposure in women, with a dose-response relationship (Sustainability, 2026 indoor air meta-analysis^[14]).

In lower-income settings, indoor combustion of biomass, coal, and other solid fuels for heating and cooking contributes meaningfully to lung cancer risk and is one of the largest drivers of LCINS globally.

6. Genetic susceptibility and family history

Having a first-degree relative with lung cancer is associated with roughly a 2-fold increased risk of lung cancer, even among never-smokers, and contributes to an estimated 26% of LCINS risk in the JAMA review (Murphy et al., JAMA, 2025^[1]).

A small number of families inherit specific cancer-predisposing variants — including the germline EGFR T790M mutation, which defines a rare hereditary early-onset lung adenocarcinoma syndrome (Journal of Thoracic Oncology, 2014^[15]). Genome-wide association studies have also identified susceptibility loci at 5p15.33 (TERT/CLPTM1L), 6p21, and 15q25, with some loci specific to East Asian populations.

Prior lung disease

Tuberculosis, COPD, chronic bronchitis, and pulmonary fibrosis are each associated with elevated lung cancer risk in never-smokers, with TB conferring an odds ratio of roughly 2.4 in pooled analyses (JCO meta-analysis, 2024^[16]). One mechanism under investigation is transcriptional remodeling of lung epithelium by pulmonary macrophages following chronic inflammation (Journal of Experimental Medicine, 2025^[17]).

Open questions

Several proposed contributors remain uncertain, and the honest answer is that the evidence does not yet support firm conclusions:

• HPV. Some studies, mostly from Taiwan, have detected HPV-16 and HPV-18 DNA in lung tumors, but methodological concerns and inconsistent Western data leave a causal role unestablished (Wang et al., Journal of Translational Medicine, 2023^[7]).
• E-cigarettes and vaping. A 2025 systematic review concluded that current evidence is insufficient to establish a causal link with lung cancer (Tobacco Induced Diseases, 2025^[18]). Cancer typically requires decades of latency, and widespread e-cigarette use is still relatively recent.
• Estrogen and reproductive factors in women — biologically plausible, but epidemiologic findings are inconsistent (Cancer, 2023^[19]).
• Aristolochic acid (from certain herbal medicines) — the 2025 Sherlock-Lung study found its characteristic mutational signature almost exclusively in Taiwanese patients, a novel finding requiring replication (Díaz-Gay et al., Nature, 2025^[2]).

---

A biologically distinct disease

The seminal 2007 review by Sun, Schiller, and Gazdar in Nature Reviews Cancer called lung cancer in never-smokers “a different disease,” and the genomic data of the past two decades have validated that framing (Sun et al., Nature Reviews Cancer, 2007^[20]).

Compared with smoking-related tumors, LCINS tumors have a lower mutation burden (typically 0–3 mutations per megabase versus 0–30 in smokers) but a substantially higher rate of targetable driver mutations — single oncogenic alterations that act as the dominant biological engine of the tumor and can be matched with a precision drug (Murphy et al., JAMA, 2025^[1]).

EGFR mutations are about four times more common in never-smoker non-small cell lung cancers than in smoker tumors (43% versus 11%), and the EGFR mutation rate climbs further — to roughly 40–60% — in East Asian never-smoker patients (Murphy et al., JAMA, 2025^[1]; Díaz-Gay et al., Nature, 2025^[2]). ALK rearrangements are roughly six times more common (12% versus 2%). ROS1, RET, HER2, and MET alterations are all enriched in never-smoker tumors as well.

This pattern has two important clinical consequences:

1. Targeted therapy is often highly effective. Third-generation EGFR tyrosine kinase inhibitors such as osimertinib have produced median overall survival exceeding 38 months in EGFR-mutant non-small cell lung cancer, and ALK inhibitors such as alectinib have produced progression-free survival exceeding 34 months (Murphy et al., JAMA, 2025^[1]).
2. Immunotherapy alone tends to work less well. Because LCINS tumors carry few mutations, they present fewer “neoantigens” for the immune system to recognize, which is why immune checkpoint inhibitors as a single agent are generally less effective in this population.

The practical takeaway frequently emphasized in current expert reviews is that comprehensive molecular profiling (next-generation sequencing) at diagnosis is essential for any patient with non-small cell lung cancer, regardless of smoking history — because identifying a targetable mutation can change treatment substantially. This is a discussion to have with the treating oncologist.

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The screening gap

Current US lung cancer screening guidelines are built almost entirely around smoking history. The 2021 US Preventive Services Task Force^[21] recommendation supports annual low-dose CT screening for adults aged 50–80 with a ≥20 pack-year smoking history who currently smoke or have quit within the past 15 years. The American Cancer Society’s 2024 update widened those criteria — but kept the smoking-history requirement in place (Medical Science Monitor, 2025 editorial^[22]).

Never-smokers — by design — fall entirely outside these criteria. The International Association for the Study of Lung Cancer has noted that current eligibility criteria can miss over 50% of lung cancers when never-smokers are excluded (Kerpel-Fronius et al., Journal of Thoracic Oncology, 2021^[23]).

The most informative real-world experiment in screening never-smokers has come from Taiwan. The TALENT study prospectively screened 12,011 asymptomatic Taiwanese never-smokers aged 55–75 with at least one risk factor (a first-degree relative with lung cancer, passive smoking, or cooking without ventilation) using low-dose CT, and detected lung cancers predominantly at early, treatable stages (Chang et al., Lancet Respiratory Medicine, 2023^[24]). In 2022, Taiwan launched the world’s first national LDCT screening program for non-smokers with a family history of lung cancer — biennial screening for women aged 45–74 and men aged 50–74 (Murphy et al., JAMA, 2025^[1]).

Comparable programs have not been adopted in the US, UK, Europe, or Australia. Concerns about overdiagnosis — particularly of indolent adenocarcinoma in situ in Asian women — are legitimate and an active area of research. Whether high-risk never-smokers in Western populations should be offered screening is one of the most important open policy questions in lung cancer prevention today.

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What prevention can look like

Most LCINS risk factors are at least partly modifiable at the population or household level. The following are general, evidence-informed concepts — not personal medical advice.

Radon.

• The EPA recommends that every home in the US be tested for radon.
• Testing is inexpensive (~$15–$25 for a DIY test kit) and widely available through state radon programs and hardware stores.
• The EPA action level is 4 pCi/L; mitigation is also worth considering between 2 and 4 pCi/L.
• Sub-slab depressurization systems typically reduce indoor radon by up to 99%.

Outdoor air quality.

• Where feasible, reducing time outdoors during high-AQI days, using well-fitted N95/KN95 respirators during severe pollution events, and supporting policies that lower PM2.5 emissions are all reasonable population-level approaches.
• HEPA air purifiers can reduce indoor PM2.5 by 50–80% and may be particularly relevant in high-pollution urban areas.

Indoor air and cooking fumes.

• Using a vented range hood, opening windows, and avoiding cooking oils past their smoke point are practical steps with biologic plausibility, especially in homes that do high-heat or wok-based cooking.

Secondhand smoke.

• Smoke-free homes and vehicles, particularly when children or non-smoking adults are present, are the most direct intervention.
• Multi-unit-housing smoke-free policies meaningfully reduce involuntary exposure.

Occupational exposures.

• Workplace respiratory protection programs, adherence to OSHA permissible exposure limits, and engineering controls (ventilation, dust suppression, substitution of safer materials) remain the core of occupational lung cancer prevention.

Family history awareness.

• Knowing whether first-degree relatives have had lung cancer is information clinicians use when discussing personal risk and the (currently limited) options for surveillance in non-smokers.

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Questions you may want to discuss with your clinician

These are general prompts for an informed conversation, not instructions:

• “Has my home ever been tested for radon? Is testing something you’d recommend in our area?”
• “Given my family history of lung cancer, are there any current surveillance options that would apply to me?”
• “What is the typical air quality in our region, and are there practical steps that might lower my long-term exposure?”
• “I have a history of [TB / COPD / chronic bronchitis / prior chest radiation]. Does that affect how you think about my long-term lung health?”
• “If I or a family member were ever diagnosed with non-small cell lung cancer, what would comprehensive molecular testing involve, and why does it matter?”

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Key takeaways

• Lung cancer in never-smokers accounts for an estimated 15–25% of all lung cancers globally, and up to 50% in parts of East Asia (Murphy et al., JAMA, 2025^[1]; Díaz-Gay et al., Nature, 2025^[2]).
• The proportion is rising, and absolute incidence appears to be rising in at least some populations, though detection improvements likely contribute as well.
• Women, East Asian populations, and people with a first-degree family history are disproportionately affected.
• Radon is the leading environmental cause of LCINS in the US, and it is the most actionable modifiable risk factor for many households (EPA^[8]).
• Outdoor air pollution (PM2.5) has both epidemiologic and mechanistic evidence supporting causation, including a landmark 2023 Nature paper on IL-1β-driven tumor promotion (Hill et al., Nature, 2023^[11]).
• Secondhand smoke, occupational carcinogens, indoor cooking and biomass fumes, and genetic susceptibility all contribute meaningfully.
• LCINS is biologically distinct, with substantially higher rates of targetable driver mutations (EGFR, ALK, ROS1, RET, HER2, MET) and a strong rationale for comprehensive molecular profiling at diagnosis.
• Current screening guidelines exclude never-smokers. Whether to extend screening to high-risk never-smokers is one of the most important open questions in lung cancer prevention.

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A note on uncertainty

The picture of LCINS we have today is far clearer than it was a decade ago, but several questions remain genuinely open: how much of the rising incidence is biology versus detection; whether HPV, vaping, or hormonal factors play a meaningful role; and whether screening can be safely extended to never-smokers without causing net harm from overdiagnosis. Future analyses from the Sherlock-Lung consortium, ongoing screening trials, and population-level air quality interventions will likely sharpen the picture over the next 5–10 years.

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