A comprehensive review led by cancer researchers at UNSW found vaping is likely to cause lung and oral cancer - even before long-term studies can confirm the exact risk.
Nicotine-based vapes, or e-cigarettes, are likely to cause cancers of the lung and oral cavity, says a new study led by UNSW Sydney and published today in Carcinogenesis.
The study 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 - or, cancer causation - 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 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 and became available in Australia around 2008. 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. Vaping is now a common sight outside schools, bars and train stations across Australia, despite the Australian government introducing new laws to regulate vapes in 2023. Disposable vapes and non-therapeutic vapes are banned, while therapeutic vapes can only be sold in pharmacies, and only to help people quit smoking.
"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," he says.
"The evidence was remarkably consistent across fields," he says. "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.
Taken 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 USA is that those who both vape and smoke are at an additional four-fold increased risk of developing lung cancer."
This was described in commentary also published today by A/Prof. Sitas and Prof. Stewart in Cancer Epidemiology.
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."
Considering all the findings - from clinical monitoring, animal studies and mechanistic data - e-cigarettes are likely to cause lung cancer and oral cancer.
