Scientists from US universities including Yale, Johns Hopkins and Princeton found that exposure to e-cigarette vapour creates a "tumor-promoting environment" in the breast and other parts of the body.
Professor Kefah Mokbel, a surgeon at the London Breast Institute at Princess Grace Hospital in London, warned that the findings should be a wake-up call for those who think the devices are harmless or better than smoking regular cigarettes.
E-cigarettes' may increase breast cancer risk, 'says new study
"This study provides good evidence that e-cigarettes have the potential to induce breast cancer, promote its development and spread to the lungs," he said.
He went on to add that it was a "misconception" that e-cigarettes were safe, and suggested they could contribute to the development of other types of cancer.
Professor Kefah Mokbel warned that the findings should be a wake-up call for those who thought the device was harmless
The study was conducted using female mice, some of which were exposed to fresh air while others were exposed to e-cigarette vapor.
Two weeks later, all were injected with breast cancer. After six weeks, tumor growth in the vapor-exposed mice almost doubled.
Mice that inhaled vaping were also more likely to develop lung metastases -- secondary lung malignancies that are usually fatal when they occur in humans.
"Young women represent a target for e-cigarette companies," the team wrote in the journal Cancer Letters, and the findings come as "e-cigarettes are becoming increasingly popular, especially among adolescents."
Young women said to represent 'target of vape companies'
Professor Charles Coombs, of the IMPERIAL Centre for Cancer Research UK, said: "The results are suggestive but not conclusive."
The news comes after reports earlier this month that e-cigarettes produce new toxic chemicals that could cause breathing and heart problems.
Ingredients used to create flavorings such as vanilla, berries and cinnamon can form dangerous mixtures when mixed with other solvents
E-cigarettes have been reported to produce new toxic chemicals and cause breathing and heart problems
Vaping is generally considered less harmful than smoking, but its safety has long been a matter of debate among experts.
Around 3.6 million British adults have used e-cigarettes in the past decade, making the UK market worth £2.5bn annually.
E-cigarette makers work by heating a liquid that usually contains nicotine, propylene glycol and flavorings, and they say vaping is far less harmful than smoking cigarettes.