Are cases of cancer in dogs and other companion animals due to chronic viruses, and if so, in what percent of cases?

The occurrence of cancer in companion animals is viral about 50% of the time, less than the 85% incidence for human beings. This is because companion animals are not a major target of the Extraterrestrial Alliance, and being more incidental are not directly targeted in the same way. This is still a significant problem, even if of a lesser magnitude statistically.