E-Cigarettes Shown to Cause Cancer in Mice

Electronic cigarettes, which deliver nicotine, are increasingly popular tobacco products. Although tobacco smoke has been proven a major threat to human health, research on electronic cigarette smoke continues. On 7 October 2019, PNAS published a new study revealing the relationship between electronic cigarettes and cancer development.

The study found that electronic cigarette smoke induced DNA damage and, in mouse lung and bladder tissue, prevented DNA repair . Nicotine induces the same types of DNA adducts and similarly inhibits DNA repair in human cells. Nicotine also increases human cells’ susceptibility to mutation and tumor development. The findings showed that electronic cigarette smoke is, in mice, a lung carcinogen (cancer-causing agent) and a potential bladder carcinogen.

Electronic cigarettes are marketed as safe alternatives to tobacco products for delivering the stimulant nicotine, and their use is increasingly popular, particularly among young people. A recent study detected extensive DNA damage in the lungs, heart and bladder mucosa of mice exposed to e-cigarette smoke. Reduced DNA repair in the lungs was also demonstrated. Nicotine and nicotine-derived nitrosamine ketone cause the same harmful effects in human lung tissue and bladder cells. These findings increase the likelihood that e-cigarette smoke, as well as nicotine, is a lung and bladder carcinogen. Since e-cigarette use has become popular over the past 10 years, the full association between its smoke and human cancers remains unknown, but this study tested and demonstrated its effects in mice.

E-Cigarette Smoke Induces Lung Adenocarcinoma

Because tobacco smokers take more than 2 years to develop lung and bladder cancer, tumor formation was examined after 54 weeks of exposure. Gross anatomical examination of mice revealed tumor-like growths in skin, the abdominal cavity, intestines and lungs. These tissues were also examined microscopically. Among exposed mice, the findings showed that, of 40 mice, 9 (22,5%) developed lung tumors. All lung tumors examined histologically by 3 pathologists were identified as adenocarcinomas.

E-Cigarette Smoke Induces Bladder Urothelial Hyperplasia

Although no visible bladder tumors were detected in any experimental group, histological examination clearly showed changes in the bladder urothelium of exposed mice (the urothelium is the thin layer lining the bladder’s inner surface, where bladder tumors most commonly arise).

Overall, among exposed mice, of 40 mice, 23(57.5%) developed growth of bladder tissue due to increased cell numbers (urothelial hyperplasia).

In conclusion, the long-term effects of e-cigarettes in humans and whether they are safer than cigarettes remain unknown; however, studies so far show devices causing adverse health effects and outcomes. They also have extremely dangerous potential through addiction, particularly nicotine addiction among young people and even children.

In 2017, e-cigarette use among high school students was 11.7%; by 2018, it had increased by 78 percent to 20.8%. In the USA, among those aged 12-17, approximately 10.7 million students have tried e-cigarettes or are open to trying them. These facts require continued attention to research and a more cautious approach.

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