Mast cell tumors (MCTs) are the most common tumor in the dog and the second most common tumor in the cat. MCTs are primarily a disease of older dogs and cats; however, extremely young dogs and cats have been reported to have MCTs. Canine breeds reported to be at increased risk for MCTs are boxers, Boston terriers, Labrador retrievers, terriers, and beagles. The only feline breed that has been reported to be at increased risk for MCTs is Siamese. Most reports show no significant gender predilection for MCTs in dogs or cats. The etiology of MCTs is presently unknown. Many have suspected a viral etiology due to MCT transplantability to susceptible laboratory dogs (extremely young or immunocompromised) with tumor cells and cell-free extracts. Recent evidence shows that a significant percentage of dogs with higher-grade MCTs have genetic mutations in c-kit (stem cell factor receptor), which may be responsible for the genesis and/or progression of MCTs in dogs. Not all dogs with MCTs have c-kit mutations, suggesting that they are not the only mechanisms for the development and/or progression of MCTs.
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