Systematic review indicates e-cigarettes likely increase risk of lung and oral cancer — Evidence Review
Published in Carcinogenesis, by researchers from UNSW Sydney, The University of Queensland, Flinders University, The University of Sydney, Royal North Shore Hospital, The Prince Charles Hospital, Sunshine Coast University Hospital
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Table of Contents
A new systematic review led by UNSW Sydney concludes that nicotine-containing e-cigarettes are likely to cause lung and oral cancers, based on a synthesis of clinical, animal, and mechanistic studies. Most related research broadly agrees that e-cigarettes expose users to carcinogens and induce cellular changes linked to cancer, though some reviews highlight the need for more long-term human studies (2 3 4 6 7 8). See the full study in the journal Carcinogenesis.
- Multiple reviews and experimental studies confirm that e-cigarette vapor contains carcinogenic substances and produces DNA damage and cellular stress in lung and oral tissues (1 6 8).
- While biomarkers and mechanistic links to cancer are well established, some reviews note that direct epidemiological evidence for increased cancer incidence among exclusive e-cigarette users is limited, largely due to the relatively recent introduction of these devices (3 7 12).
- Several studies emphasize that the combination of vaping and traditional cigarette smoking ("dual use") may significantly amplify lung cancer risk, and that young people may be especially vulnerable (2 4 5 15).
Study Overview and Key Findings
Recent years have seen a rapid increase in e-cigarette use, especially among young people, amid ongoing debates about their safety and potential to help smokers quit. This comprehensive review, published in Carcinogenesis, represents one of the most extensive efforts to date to evaluate whether vaping itself—not just as a gateway to smoking—can directly cause cancer in humans. By integrating findings from multiple disciplines, the research team aimed to clarify the carcinogenic potential of e-cigarettes in the absence of long-term population data.
| Property | Value |
|---|---|
| Organization | UNSW Sydney, The University of Queensland, Flinders University, The University of Sydney, Royal North Shore Hospital, The Prince Charles Hospital, Sunshine Coast University Hospital |
| Journal Name | Carcinogenesis |
| Authors | Prof. Stewart, A/Prof. Freddy Sitas |
| Methods | Systematic Review |
| Outcome | Cancer risk from vaping, carcinogenicity of e-cigarettes |
| Results | E-cigarettes likely cause lung and oral cancer. |
The study found consistent evidence across laboratory, animal, and clinical research that e-cigarette aerosols contain multiple carcinogens and induce DNA and tissue changes associated with cancer risk. While the review does not provide a quantitative risk estimate, it concludes that vaping is likely to increase the risk of lung and oral cancers independent of traditional smoking.
Literature Review: Related Studies
To place these findings in context, we searched the Consensus database (over 200 million papers) using the following queries:
Below, related studies are grouped by major research questions:
| Topic | Key Findings |
|---|---|
| What carcinogens and biological changes are associated with e-cigarette use? | - E-cigarettes emit known carcinogens (e.g., nitrosamines, PAHs, heavy metals) and consistently induce DNA damage, oxidative stress, and genotoxicity in lung and oral cells (1 2 4 6 8). - Users of e-cigarettes show increased biomarkers of DNA damage and cellular changes consistent with carcinogenesis (1 6 8 9). |
| Do e-cigarettes increase risk of lung and oral cancers in humans? | - Evidence from animal and cellular models supports increased cancer risk, but direct epidemiological evidence in humans is limited due to short follow-up; case reports and biomarker studies suggest a plausible risk (1 3 7 10 12). - Clinical reviews highlight insufficient but growing evidence of cancer risk, with further research recommended (3 7 12 13 14). |
| How does dual use or secondhand exposure affect cancer risk? | - Dual users (both vape and smoke) may have a substantially higher risk of lung cancer than exclusive smokers or vapers (2 4 5). - Secondhand exposure to e-cigarette aerosol poses lower cancer risk than tobacco smoke but is not risk-free, particularly for children and bystanders (5 11 12). |
| What are the broader health implications and knowledge gaps regarding e-cigarette safety? | - E-cigarettes may be less harmful than cigarettes, but their long-term safety profile is unknown, and they are associated with addiction, inhalation injuries, and oral health deterioration (12 13 14 15). - Regulatory reviews call for higher-quality, long-term clinical and epidemiological studies to resolve remaining uncertainties (3 12 13 14). |
What carcinogens and biological changes are associated with e-cigarette use?
Multiple studies consistently find that e-cigarette vapors contain known carcinogens and induce biological changes associated with increased cancer risk. These effects have been demonstrated through laboratory and animal studies, as well as biomarker analyses in human users. The new review in Carcinogenesis synthesizes these findings, arguing that the mechanistic and toxicological evidence aligns in supporting a carcinogenic potential for vaping.
- E-cigarette aerosols contain nitrosamines, polycyclic aromatic hydrocarbons (PAHs), heavy metals, aldehydes, and other carcinogens (1 2 4 6 8).
- Animal and in vitro studies show increased DNA damage, oxidative stress, and mutations in exposed tissues (1 6 8).
- Clinical biomarker studies reveal elevated levels of DNA adducts and other markers linked to cancer risk in e-cigarette users (6 8).
- Laboratory studies indicate e-cigarette exposure may induce chemotherapy resistance in cancer cells (9).
Do e-cigarettes increase risk of lung and oral cancers in humans?
While mechanistic and preclinical data support a cancer risk, direct evidence from long-term human studies is still emerging. The new systematic review is notable for integrating these lines of evidence, but acknowledges the lack of large-scale, long-term epidemiological data. Several reviews and case reports suggest caution and highlight the need for ongoing monitoring.
- Animal models and cellular studies show clear cancer-promoting effects, but epidemiological studies in humans are limited by the recency of e-cigarette introduction (1 3 7 10 12).
- Several reviews find substantial biomarker-based evidence of risk, but insufficient direct evidence of increased cancer incidence among exclusive vapers (3 7 12 13).
- Case reports have documented oral carcinomas in chronic e-cigarette users (10).
- Systematic reviews call for more rigorous, long-term studies to establish causality (3 7 12 13 14).
How does dual use or secondhand exposure affect cancer risk?
There is mounting evidence that "dual users"—individuals who both vape and smoke traditional cigarettes—face higher cancer risks, and that secondhand exposure to e-cigarette aerosol is not without harm, though generally lower risk than tobacco smoke. The new review echoes these concerns, citing studies that suggest dual use is common and hazardous.
- Epidemiological evidence suggests dual users have a four-fold increased risk of lung cancer compared to exclusive users of either product (2 4 5).
- Secondhand exposure to e-cigarette aerosol results in measurable intake of carcinogenic compounds, though the risk is lower than with tobacco smoke (5 11 12).
- Reviews highlight concerns for children and non-smokers exposed to e-cigarette aerosols in indoor environments (11 12).
- Regulatory guidance increasingly addresses both dual use and environmental exposure (12 15).
What are the broader health implications and knowledge gaps regarding e-cigarette safety?
While some studies suggest that e-cigarettes may be less harmful than combustible tobacco, there is consensus that their long-term health effects remain uncertain. The new review emphasizes the need to avoid repeating historical delays in recognizing tobacco's harms, highlighting the importance of proactive public health policies.
- E-cigarettes are associated with addiction, inhalation injury, burns, and a range of adverse oral health effects, including changes to the oral microbiome and mucosal health (6 12 13 14 15).
- Evidence for their effectiveness as smoking cessation aids is limited and inconsistent (12 14).
- Long-term risks, including cancer, cardiovascular, and developmental outcomes, remain under-studied (3 12 13 14).
- Many reviews call for more high-quality, long-term studies and improved regulatory oversight (3 12 14).
Future Research Questions
While the evidence for the carcinogenic potential of e-cigarettes is growing, significant uncertainties remain, especially regarding the magnitude of cancer risk in humans and the effects of long-term, exclusive use. Addressing these knowledge gaps will require new studies with longer follow-up, larger populations, and better characterization of exposure patterns.
| Research Question | Relevance |
|---|---|
| What is the long-term incidence of lung and oral cancers in exclusive e-cigarette users? | Long-term epidemiological data are lacking, making it difficult to quantify cancer risk in exclusive vapers; most current evidence is from animal, laboratory, or biomarker studies (3 7 12). |
| How do specific e-cigarette flavorings and device types affect carcinogen production and cancer risk? | The composition of e-liquids and devices varies widely, potentially impacting the level and type of carcinogens emitted; more research is needed on how these factors influence health outcomes (2 4 6 14). |
| What is the impact of dual use of e-cigarettes and tobacco on cancer risk? | Dual use appears to increase cancer risk beyond that of either product alone, but the magnitude and mechanisms require further clarification (2 4 5). |
| What biomarkers can best predict future cancer risk in e-cigarette users? | Several biomarkers of DNA damage and genotoxicity have been identified, but their predictive value for actual cancer development remains unproven (1 3 6 8). |
| How does secondhand exposure to e-cigarette aerosol affect cancer risk in children and non-users? | While secondhand exposure is generally lower risk than tobacco smoke, the health impact on vulnerable populations is not well characterized and warrants further study (5 11 12). |
This article provides an objective summary of current evidence linking e-cigarette use to increased cancer risk, highlighting where the findings from the new UNSW Sydney-led review align with or diverge from related research. As vaping continues to grow in popularity, especially among younger populations, ongoing research and careful monitoring will be essential to inform public health policy and clinical recommendations.