The carcinogenicity of e-cigarettes: a qualitative risk assessment

This review involves a qualitative carcinogenic risk assessment of nicotine-based e-cigarettes. Though direct epidemiological evidence of cancer causation takes time to accumulate, carcinogenicity of e-cigarettes is evident from different types of investigation including, with respect to studies in humans, some case reports but mainly involving monitoring of biomarkers of exposure and biomarkers of harm implicating tumorigenesis. Complementary laboratory investigations of e-cigarette aerosols and constituent chemicals include rodent bioassays and a range of approaches to elucidate mechanism(s). In respect of e-cigarettes, each of these types of investigation have been subject to successive reviews, sometimes more than once per year. Consequently, this over-arching review is restricted to publications since 2017 to avoid possible selection bias. Physiological evidence of exposure using biomarkers reveals DNA damage correlated with vape-derived metabolites attributable to carcinogens including nicotine-derived nitrosamines, volatile organic compounds, flavour-derived agents, and certain metals. Biomarkers also indicate vaping-attributable oxidative stress, epigenetic change and inflammation in oral and respiratory tissue often specified in comparison with smoking. Rodent bioassays include inhalation exposure of mice to e-cigarette aerosol described as causing lung adenocarcinomas. Mechanistic data are presented using the key characteristics of carcinogens and taken together implicate a complex mixture mediating carcinogenicity via genotoxic and other processes. From 2017 to 2025, the conclusions in e-cigarette reviews addressing different avenues of investigation moved from describing a need for more evidence to notifying concern about e-cigarette carcinogenicity. Nicotine-based e-cigarettes are likely to be carcinogenic to humans who use them causing an indeterminate burden of oral cancer and lung cancer.