From the pesticides used in agriculture, insecticides and cleaners used in households, and solvents used in paints to toys made of synthetic products and artificial preservatives and additives in our food, man-made chemicals and pollutants are everywhere. With so many synthetic chemicals around us, could some of these products—as well as other aspects of our environment—be causing cancer in our canine companions?
Dr. Larry Glickman, veterinarian and epidemiologist at Purdue University, has no doubt that they do. “Of course. There are many chemicals and environmental factors known to cause cancer in people, and many may also cause cancer in pets. The problem,” he observes, “is that these are far better studied in humans than in pets.”
The dearth of study is a matter of both convenience and money. Says Glickman, “With humans, there are mandatory reporting systems for disease—such as death certificates, [which list the] immediate and underlying cause of death.” As a result, agencies can track how frequently certain diseases result in death, and thereby accumulate information as to whether there is an increase or decrease in specific cancers, for example. “With animals, we don’t have anything,” say Glickman. “We just have scattered pieces of data to look at frequency of diseases.” These include hospital records or, increasingly, insurance claim records. But, Glickman emphasizes, “This is way behind what has been done in humans.”
Clear Links Exist
Despite the scarcity of studies, some research has identified clear links between cancer in dogs and environmental factors. For instance, a 1983 study by Glickman and his colleagues revealed that dogs with a mesotheliomas (a rare tumor of the chest cavity) were more likely to have lived in households where owners had exposure to asbestos, or to have gone with their owners to workplaces in which asbestos materials were handled (e.g., shipbuilding and brake repair). Additionally, chrysolite asbestos fibers were found in significantly higher amounts in the lung tissue of these dogs than in dogs with other types of lung tumors and no history of exposure to asbestos.
In another example, Glickman notes that “exposure to cigarette smoke has been shown to increase nasal cancer in dogs.” Long-nosed dogs are two times more likely to develop nasal cancer if they live with a smoker than if they are not exposed to cigarette smoke, and the incidence of canine nasal cancer increases with the number of packs the human in the household smokes per day. Similarly, short-nosed dogs are twice as likely to develop lung cancer if they live in a house with cigarette smokers. In these dogs, cotinine levels (a metabolite of nicotine) in the urine are high compared to those of dogs in nonsmoking households. Taken together, these findings suggest that the longer air-filtration system of long-nosed dogs serves to protect them from lung cancer but also predisposes them to developing nasal cancer.
Glickman’s own research has revealed other environmental risks. As he reported in 1989 in the Journal of the American Veterinary Medical Association, female dogs exposed to insecticides in flea sprays and dips are at higher risk of developing bladder cancer than those on whom such products are not used. As with nicotine, the compounds in dips and sprays are absorbed into the bloodstream. The body gets rid of these products by excreting them into the urine. The risk is further enhanced in overweight females, most likely because the compounds, once absorbed, are retained in fat. Animals with more fat retain more of the chemicals. And finally, risk was also elevated in females who lived close to a second potential source of insecticides—a marsh that had been sprayed for control of mosquitoes, for example.