This proposal addresses the need to develop biological markers specific to canine cutaneous mast cell tumors (MCT) that can be used to quantitatively, efficiently and accurately to predict tumor behavior. In dogs, mast cell tumors are one of the most common cancers, comprising up to 21% of all canine skin cancers. Clinical outcomes of cutaneous MCT can vary from easily cured isolated tumors to fatal metastases. Failure to accurately predict the outcome can result in patients being subjected to painful and expensive treatments unnecessarily or, conversely, not getting the intensive treatment they need. The current markers for MCT only accurately predict outcome in a small number of patients. Moreover, these techniques are subjective and labor-intensive. A major effort is underway to develop molecular and biological tests for diagnosis and prognosis in human oncology. Dr. Davis intends to apply this approach to canine cutaneous MCT, through active collaborations between pathologists at Tufts Cummings School of Veterinary Medicine and veterinary oncologist and molecular biologists at the Broad Institute who have identified a number of unique potential biomarkers for canine MCT.