A recent study shows a possible link between vaping and cancer, extending the trend’s dangers beyond a deadly pulmonary disease.

The first study linking vaping to cancer found nearly 25% of mice developed lung cancer after 54 weeks of exposure to e-cigarette vapors containing nicotine. More than half the mice developed hyperplasia.

A control group of mice exposed to nicotine-free vapors had no cases of lung cancer and one case of hyperplasia.

The New York University study had a small sample size — 40 mice — and the rodents experienced full-body exposure since they can’t inhale vapor as deeply as humans. Nonetheless, researchers concluded that more research needs to be conducted on the possible link.

“Even if there isn’t smoke, there is still risk,” said George J. Mikos, M.D., cardiothoracic surgeon with Norton Cardiothoracic Surgery. “In addition to the recent increase of fatal pulmonary illnesses linked to vaping, we now know cancer is a real possibility.”

Dr. Mikos advises patients to err on the side of caution, considering how little is known about vaping’s long-term effects. After all, e-cigarettes have been sold commercially in the United States for only a little over a decade.

The National Institute on Drug Abuse reports that 66% of teens believe that they’re only vaping flavoring and nothing else. In reality, 99% of e-cigarettes sold in the U.S. contain nicotine. The Food and Drug Administration has warned that young people and pregnant women shouldn’t use any vaping product.

The Centers for Disease Control and Prevention has determined that e-cigarette vapor contains “ultrafine particles, chemicals leading to lung disease such as diacetyl, volatile organic compounds, cancer-causing chemicals, and heavy metals such as nickel, tin, and lead.”