Mast Cell Tumors

Mast cell tumors are the most common skin tumor in dogs. They can occur at any location and affect any age or breed of dog. However breeds such as the Boxer, Boston Terrier, Chinese Pug and Labrador Retriever, are overrepresented and may be genetically predisposed to developing MCT. Mast cell tumors are highly variable in their behavior, with some being small masses easily cured with surgery and others being invasive and rapidly spreading to lymph nodes and elsewhere in the body. Diagnosis is readily accomplished with a fine needle aspirate. Mast cell tumors are most commonly removed surgically. If it is not possible to completely remove a mast cell tumor, radiation therapy may be recommended. For more aggressive tumors that are likely to, or have already metastasized, chemotherapy is used. Predictive factors help determine the likely behavior of a mast cell tumor. Most important is the grade of tumor, which is how aggressive it appears on biopsy. Mast cell tumors are graded 1-3, with grade 1 being the most benign and grade 3 being highly malignant. Other factors associated with more aggressive behavior include where the tumor is located on the body and evidence of spread of the tumor. Another factor associated with outcome a genetic mutation of c-kit, the receptor for a growth factor shown to be mutated in many dogs with mast cell tumors. Interestingly, this growth factor receptor is also mutated in human cancers such as gastrointestinal stromal tumors (GIST). Therapies targeting c-kit have been evaluated in dogs with mast cell tumors, then moved into clinical trials for people with GIST. Because of the similarity in genetic mutations, canine mast cell tumors can be used to model other diagnostic and therapeutic investigations. The CCOGC supports further investigations by providing tissue and blood samples from canine mast cell tumor patients to researchers looking into this fascinating area.

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