A scientific review has raised fresh concerns about the long-term cancer risks of vaping, concluding that e-cigarettes are probably carcinogenic, while also acknowledging significant gaps in the evidence.
The analysis of reviews and single studies published since 2017 concluded that nicotine vaping “likely” contributes to oral and lung cancers. But the actual risks and how they compare with those from smoking are impossible to calculate at this point.
E-cigarettes are relatively new, having hit the market about 20 years ago. Unlike the case with tobacco use, where decades of epidemiological data firmly establish its cancer risk, long-term population studies of e-cigarette users are lacking.
“Sufficient time to reveal any consequential burden of cancer wholly attributable to vaping has not yet passed,” said Bernard Stewart, PhD, a professor at the University of New South Wales in Sydney, Australia, who led the review.
The upshot, in the words of one researcher, is that society is in the midst of a “natural experiment” to see what the ultimate health risks of vaping are.
The State of the Evidence
When first introduced, e-cigarettes were touted as being a less harmful alternative to traditional smoking and possibly a way to help smokers quit. A recent Cochrane Review concluded that nicotine-based vaping can, in fact, boost quit rates compared with nicotine replacement products.
And on May 5, the FDA announced a first: It authorized the marketing of fruit-flavored vapes, citing a need for an “expanded array of flavored options” for adults who want to give up traditional cigarettes.
At the same time, no e-cigarette product is FDA-approved for smoking cessation, and health authorities have for years raised concerns about vape marketing that targets adolescents, as well as the lack of data on long-term health risks.
Enter the new review, published in Carcinogenesis. Stewart’s team compiled the most up-to-date evidence on the “carcinogenicity” of e-cigarettes, using biomarker studies of people who vape, case reports, animal research, and analyses of e-cigarette aerosols.
Starting with people: Numerous studies have established that vapers are exposed to known or suspected carcinogens. E-cigarette users have elevated urinary markers of volatile organic compounds, such as acrylamide and acrylonitrile, vs nonusers. They also have higher levels of metals such as lead and cadmium, as well as certain polycyclic aromatic hydrocarbons.
In nearly all of those cases, vapers show far lower exposure than cigarette smokers do. Still, biomarker studies have pointed to potential consequences from e-cigarette chemical exposures, including elevated indicators of DNA damage, oxidative stress, chronic inflammation, and epigenetic changes in tissue samples from vapers compared with controls (typically identified as nonsmokers).
Meanwhile, lab studies of e-cigarette aerosols have turned up all 10 “key characteristics” of carcinogens, including the capacity to alter DNA repair, induce inflammation, and suppress immune system activity. And based on animal research, exposure to those aerosols can cause lung tumors.
The main gap? Data on human cancer are scarce. Stewart and his colleagues cite case reports of oral cancers among people who vaped for over a decade. And together with the other data sources, they consider the evidence strong enough to call e-cigarettes a likely contributor to oral and lung cancer risk.
But to “move beyond isolated case reports,” the researchers say, longitudinal studies linking e-cigarette use to cancer incidence in population-based registries are necessary.
The review was restricted to nicotine-delivering e-cigarettes and did not assess marijuana vaping. There is early research suggesting that cannabis aerosols trigger inflammation, apoptosis, and “cancer pathways” in human bronchial cells, but the evidence base is even more limited than that for e-cigarettes.
Why Certainty Remains Elusive
A chief reason for the uncertainty is the long latency of cancer.
“The evidence from biomarkers is consistent, but the magnitude of the effect long term in human studies will likely take much more time to be known,” Michael Chaiton, PhD, of the Center for Addiction and Mental Health and Ontario Tobacco Research Unit, University of Toronto, Toronto, Canada, told Medscape Medical News.
Product variation is another factor. E-cigarettes differ in device design and e-liquid composition, while user behavior varies, too — all of which make it difficult to quantify exposure or compare studies.
It’s also tough to tease out the effects of e-cigarettes, per se, from those of cigarette smoking, because many people are “dual users,” Stewart pointed out.
Chaiton agreed, noting that this type of research is “inherently tricky.”
“It’s hard to find large groups of people who have never smoked cigarettes but have been frequent vapers for a long time,” he said. “That’s particularly true for older people.”
Essentially, Chaiton said, “as a society, we are currently running a natural experiment,” where health risks attributable to vaping itself may only become clear in younger cohorts.
The Bottom Line
While many questions remain, it is safe to make certain assumptions based on the existing evidence, according to Chaiton.
“First,” he said, “there are harms associated with vaping exposure compared to non-exposure. Second, harms associated with vaping will be less than harms associated with smoking for most diseases, including cancer. The level of biomarker exposure is good evidence for that.”
However, the relative disease risks — how much worse is vaping than nonuse and how much better is it than smoking nonexposure — remain to be seen, Chaiton said. And those are critical unknowns from a public health standpoint.
“The challenge,” Chaiton said, “is that from a policy perspective, it does make a difference if vaping is 30% as harmful as smoking, or 5%.”
https://www.medscape.com/viewarticle/does-vaping-cause-cancer-2026a1000euv
