In defining “a lot” and “not much,” Glickman notes that “this speaks to the concept of attributable risk, which is the proportion of a specific type of cancer that can be attributed to a specific exposure such as insecticides. Attributable risk is a function of how many individuals in a population are exposed to insecticides plus the risk of cancer associated with insecticides. Thus, a chemical associated with a small increased risk of bladder cancer is important if a high proportion of dogs are exposed. In contrast, a chemical like asbestos is associated with a very high risk of mesothelioma, but very few dogs are exposed, and the attributable risk is thought to be low in people (about 5 percent of all lung cancers). In contrast, the attributable risk for lung cancer (90 percent) associated with smoking is very high even though the risk of lung cancer associated with smoking is relatively low, since so many people smoke.”

Both Glickman and Moore stress the need for more studies. It’s not accurate to assume that if an individual pet gets cancer, it must be due to some factor noticed to be different in the environment—many factors may change simultaneously. For instance, says Moore, “When people were first looking at causes of Down Syndrome in humans, they found that the sixth child was much more likely to have Down Syndrome. So that was thought to be a risk factor. But it was really the age of the mother at birth.”

Clearly, careful studies that take a myriad of potential risk factors into consideration are needed—for example, comparing dogs who develop a specific cancer to similar groups of cancer-free dogs, and even similar groups with other types of cancer—in order to identify potential correlations. This sort of research, which involves a multitude of animals who are followed throughout their lifetimes, is expensive, often running into millions of dollars. The adage “forewarned is forearmed” applies here, however; understanding the connections between genetic predispositions and environmental risk factors gives us the information we need to make better decisions about the dogs we love and care for—decisions that could potentially improve the quality and length of their lives. And that benefit is priceless.
 
In 2007, the Morris Animal Foundation launched “Canine Cancer Cure,” a $30 million effort to cure canine cancer. This effort involves fundraising and managing and administering research grants to veterinary colleges and research organizations. Check for updates on their progress.

Originally published under the title: “The Canine in the Coal Mine.”