Which small animal is most commonly affected by mast cell tumors?

Mast cell tumors are most commonly seen in dogs, making them the correct answer. This prevalence is particularly notable in certain breeds, such as Boxers, Bulldogs, and Labradors, which are predisposed to developing these tumors. Mast cell tumors arise from mast cells, which are a type of white blood cell involved in allergic responses and inflammation. In dogs, these tumors can vary widely in behavior, ranging from benign to highly aggressive, and they can occur in various locations on the body.

In contrast, while cats can also develop mast cell tumors, they do so at a significantly lower rate compared to dogs. Ferrets and rabbits are much less commonly reported with mast cell tumors compared to dogs and cats, making their incidence negligible in this context. Therefore, the higher occurrence of these tumors in dogs is a critical factor in identifying the correct response to this question.