If you google “Research’s best friend” the first article is a story about how researchers have developed a vaccine that has been very helpful to dogs with naturally occurring lymphoma and that someday might be used in people.
The article makes it sound like testing vaccines on naturally sick dogs and cats might help speed up the progress on cancer vaccines, since dogs and cat cancers have alot in common with human cancers, as well as possibly helping the animals. There is greater variation in such naturally occurring cancers than in the cancers they put into mice.