Scientific American has an interesting article about the study of dogs. And not just dogs as laboratory animals, but epidemiological studies of pet dogs.
It makes sense. Pet dogs can live to be quite old (for dogs) and many develop cancer. Bone cancer is particularly common in dogs. Further, dogs have been living with humans and have been exposed to more or less the same environment. Laboratory studies, which are frequently done on rodents, are controlled situations where the animal is fed or injected with suspect carcinogens or treatments. These can yield some good results, but this epidemiological and other information from animals that actually live with humans on a closer scale to humans can also be beneficial to researchers. They can also do experiments on pet dogs to see what treatments are effective in them before trying the treatments on humans.