Nicotine-based vapes (e-cigarettes) are likely to cause cancers of the lung and oral cavity, according to a new study led by UNSW Sydney and published in Carcinogenesis. The study is titled “The carcinogenicity of e-cigarettes: a qualitative risk assessment.”
The work analyses a wide body of global research and was led by UNSW cancer researcher Adjunct Professor Bernard Stewart AM, with investigators from The University of Queensland, Flinders University, The University of Sydney, as well as Royal North Shore, The Prince Charles and Sunshine Coast University hospitals.
The team brought together experts from multiple disciplines, including pharmacists, epidemiologists, thoracic surgeons, and public health researchers. Together, they examined the evidence from different scientific perspectives.
“To our knowledge, this review is the most definitive determination that those who vape are at increased risk of cancer compared to those who don’t,” Prof Stewart says.
This assessment of carcinogenicity review argues that while researchers have long focused on vaping as a gateway to smoking, less attention has been paid to whether the devices might cause cancer on their own.
It is one of the most detailed attempts yet to determine whether vaping itself may cause cancer, independent of tobacco smoking. The analysis draws together clinical studies, animal experiments, and laboratory research examining the chemicals produced by e-cigarettes.
“Considering all the findings—from clinical monitoring, animal studies and mechanistic data—e-cigarettes are likely to cause lung cancer and oral cancer,” Prof Stewart says.
He says that though the consistency of findings across those disciplines was striking, the exact number of attributable cancer cases remains unclear.
“Our assessment is qualitative and does not involve a numerical estimate of cancer risk or burden. We’ll only be able to determine the precise risk once longer-term studies are available.”
Growing public health concerns
E-cigarettes were first sold in the early 2000s. Early marketing framed them as a “safer” alternative to tobacco cigarettes, as well as a possible aid for quitting smoking.
But the colourful, flavoured devices of today have spread quickly and widely, particularly among young people.
“E-cigarettes are known to be a gateway to smoking and hence cancer,” says co-author UNSW Associate Professor Freddy Sitas. “But the extent to which they may cause cancer in their own right has not received as much attention in research. The evidence was remarkably consistent across fields. It dictated an unequivocal finding now, though human studies that estimate the risk will take decades to accumulate.”
A clear outcome
Smoking has been studied for more than a century. Though e-cigarettes are relatively new, inhaling nicotine-laced aerosols is already linked to addiction, poisoning, inhalation injuries, and burns.
While researchers wait for long-term population studies showing whether people who vape are more likely to develop cancer, they must rely on multiple other forms of evidence.
The team identified numerous carcinogenic compounds in e-cigarette aerosols, including volatile organic chemicals and metals released from heating coils.
They examined several types of evidence: biomarkers in people showing DNA damage, oxidative stress, and tissue inflammation; experiments in mice that caused lung tumours; and laboratory studies showing cellular damage and disrupted biological pathways linked to cancer.
Taking all the results together, the researchers say the evidence points strongly in one direction.
A compounding problem
There is also growing evidence that many smokers who switch to vaping don’t quit cigarettes.
“Most of those who use e-cigarettes to quit smoking end up in ‘dual-use limbo,’ unable to shake off either habit,” says A/Prof Sitas. “What we do know from recent epidemiological evidence from the U.S. is that those who both vape and smoke are at an additional four-fold increased risk of developing lung cancer.”
History repeating
A/Prof Sitas and Prof Stewart traced parallels between the early scientific evidence linking smoking to disease and emerging concerns about vaping.
It took nearly a century of scientific investigation—from the mid-1800s to the landmark US Surgeon General’s report in 1964—before smoking was officially recognised as a cause of lung cancer.
During that time, early warning signs were often dismissed or overlooked.
“Early reports linked smoking to infectious diseases such as tuberculosis, followed by cardiovascular disease, stroke and lung cancer,” A/Prof Sitas says.
He says the same pattern may now be unfolding with vaping, and that researchers should not repeat the delay that occurred with cigarettes.
“E-cigarettes were introduced about 20 years ago. We should not wait another 80 years to decide what to do.”
Source: University of South Wales
