Canine Mast Cell tumors – More Changes on the Horizon

Carrie Wood DVM, DACVIM (Oncology)

Mast cell tumors are the most common cutaneous neoplasms of the dog.  Most veterinarians in private practice will surgically manage many of these tumors during their career.  These tumors can vary widely from a single benign cutaneous mass to multi-focal, rapidly progressive lesions.  The cornerstone of treatment has always been surgery followed by careful pathologic review to determine completeness of excision and when and if follow up treatments are warranted. 


Currently most pathologists use the Patnaik 3-tier grading system.  With this system, unfortunately the morphologic criteria used to determine grade 2 tumors can vary between pathologists.  Some pathologists will refer to high and low grade 2 tumors but this is not based on reproducible criteria.  A recent proposal from the American College of Veterinary Pathologists recommends a revised two-tier grading system.  When 95 samples were reviewed using the Patnaik system by 28 independent pathologists (blinded to the results) there was 75% concordance for Grade 3 mast cell tumors and less than 64% for the diagnosis of Grade 1 and 2 tumors. 

 High grade mast cell tumor


When the revised two tier system was used there was 100% concordance for high grade mast cell tumors with 96.8% consistency (2 pathologists included an additional two tumors in the high grade category).   This high grade category was associated with increased mortality and a median survival of 4 months.  In the low grade category survival was greater than 2 years.  Statistical analysis of the data showed that the 2-tier system is a better predictor of survival than the more commonly used Patnaik system.


Our pathologists at Angell plan on utilizing this objective 2-tier system to allow us to adequately plan follow up for patients. This system, in addition to the having electron beam radiation therapy added to our armament, allows us to offer the optimal treatment outcomes for canine patients afflicted with mast cell disease.


For more information about Angell Animal Medical Center’s Oncology service, please visit Angell’s Oncology doctors are available for consultation via phone or e-mail ( To contact Angell’s Oncology doctors by phone or to refer a patient to the Angell Oncology service, please call 617-541-5136.