Quick Facts at a Glance
20-25% of all skin/subcutaneous tumors in dogs are mast cell tumors (MCT)
10-15% of canine MCT are clinically indistinguishable from subcutaneous lipomas (fatty tumors)
Definitive diagnosis of MCT cannot be made without cytologic (aspirate) or histologic (biopsy) evaluation of the lesion
Behavior of individual MCTs is difficult to predict but should always be considered aggressive until proven otherwise
MCT of the perineal and inguinal regions tend to behave more aggressively than their tumor grade would predict
Most dogs with MCT have a normal CBC(complete blood count)
20% of dogs with MCT will have multiple primary tumors in their lifetime
Aggressive surgical resection remains the cornerstone of treatment
What are the clinical features?
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Mast cell tumors in dogs occur primarily as either a skin or subcutaneous mass. It is important to remember that mast cell tumors are extremely variable in their clinical presentation. They can resemble any other type of skin or subcutaneous tumor, both benign (i.e. lipoma) and malignant. Most canine MCT are solitary although multiple primary tumors develop in 20% of patients. Approximately 50% of canine MCT are located on the trunk and perineum, 40% on the extremities and 10% on the head and neck.
Regional lymphadenopathy (lymph node enlargement) may occur when high-grade mast cell tumors metastasize (spread) to draining lymph nodes. Hepatomegaly (liver enlargement) and splenomegaly (spleen enlargement) are features of advanced stage, metastatic MCT. Malignant mast cells may be detected in the blood and bone marrow of dogs with advanced stage disease.
Cytology vs. histopathology?
The diagnosis of MCT is often made simply with cytologic evaluation of a fine needle aspirate of the mass. Although cytology may allow us to confirm the diagnosis, it provides little prognostic information. Histopathology (biopsy) allows us to grade the tumor so we can predict biologic behavior and make appropriate treatment recommendations.