A few months ago, a tyrosine kinase inhibitor anticancer drug for people, this month, one for dogs.

It is made to treat cutaneous mast cell tumors, which apparently account for about a quarter of dog cancers.
I know a lot of people drugs end up in pets, but do pet drugs ever end up crossing over into human medicine? Anyone know anything about how the decision to go after a dog-specific drug works? Just cheaper to go after?