Exposure to cigarette smoke increases the risk of cancer in dogs

A study of Scottish Terriers shows that exposure to secondhand smoke is associated with bladder cancer in dogs. The results highlight the importance of preventing this exposure to secondhand smoke. These findings could help identify the gene-environment interactions underlying bladder cancer in both dogs and humans.

The devastating effects of smoking on human health have been known for decades, but this new study further strengthens our understanding of the link between cancer in dogs and a smoke-filled environment. A mixture of smoke exhaled by smokers and smoke emitted from lit cigarettes, secondhand smoke is involuntarily inhaled by those around them, including animals. This ambient smoke contains more than 7,000 chemicals, 69 of which are recognized as carcinogens…

Canine urothelial carcinoma is a form of cancer that affects the cells of the bladder epithelium in dogs. It is a malignant tumor that generally develops from the bladder lining and can spread to surrounding tissues and nearby organs. Symptoms of this disease may include frequent urination, pain during urination, blood in the urine, loss of appetite, and weight loss. Early diagnosis and appropriate treatment are essential to improve the survival chances of a dog with urothelial carcinoma, even though this bladder tumor is most often fatal.

The risk of bladder cancer is higher in certain dog breeds that are predisposed to it. For example, the Scottish Terrier is twenty times more likely to develop this tumor than other breeds. This is why it was selected for this comparative study with bladder cancer in humans. The objective was to identify environmental risk factors and those related to the affected animal.

Urinary concentrations of cotinine (an alkaloid found in tobacco and the predominant metabolite of nicotine) were measured, and the results revealed bladder cancer in 32 of the 120 dogs screened, which was significantly associated with lifestyle, regardless of whether the household included smokers or not. Scottish Terriers exposed to cigarette smoke over a three-year period were six times more likely to develop bladder cancer than other dogs with little or no exposure to secondhand smoke. However, cotinine was detected in the urine of dogs living in smoke-free environments, suggesting that they were exposed to tertial smoke—the smoke that remains trapped in hair, skin, fabrics, carpets, walls, and can persist for years on these surfaces, even after the odor has disappeared.

Smoking is also a key risk factor in half of all cases of human urothelial carcinoma, increasing the risk three to four times compared to nonsmokers. The scientists conclude that their findings could help shed light on the links between carcinogens and the development of certain cancers in humans. These latest findings may also confirm that dogs serve as sentinels for environmental risks: their shorter lifespans make it easier to study exposure to a carcinogen, whereas it can sometimes take decades for the effect to manifest in humans.

Finally, the study should encourage dog owners to refrain from smoking to protect their pets, keeping in mind that secondhand smoke is even more harmful than firsthand smoke since it contains three times as much tar, twice as much nicotine and carbon monoxide, 51 times more formaldehyde, and 44 times more ammonia!