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Grading Mast Cell Tumors

There are three grades of mast cell tumors: Grade I (well-differentiated), Grade II (moderately differentiated) and Grade III (poorly differentiated). The type of treatment your pet receives depends on the tumor’s grade.

Grading Mast Cell Tumors


If your dog has a Grade I mast cell tumor, its removal is likely the only treatment necessary. Grade II can also be treated by surgical excision only, but the veterinarian will likely run tests to ensure the cells haven’t spread to other locations in your dog’s body.

With Grade III, the veterinarian will still monitor your pet for metastasis and will also prescribe a combination of chemotherapy and radiation, as surgery alone isn’t effective in treating the advanced grade.

Grades I and II carry an excellent prognosis when treated quickly and effectively. The outlook for Grade III should be much more guarded, as recurrences of the cancer are more likely. To ensure your dog has the best outcome possible, keep an eye out for growths and have them examined immediately.


Degner, Daniel A. “Mast Cell Tumors in Dogs and Cats.” Vet Surgery Central. 2004. (April 30, 2011)

Howell Book House. “Melanomas, Squamous Cell Carcinomas, and Mast Cell Tumors in Dogs.” WebMD. 2007. (April 30, 2011)

NC State University College of Veterinary Medicine. “Mast Cell Tumors in Dogs.” (April 30, 2011)

Pet Cancer Center. “Mast Cell Tumors in Dogs.” Feb. 12, 2011. (April 30, 2011)

Philibert, Jeffrey. “Mast Cell Tumors (Mastocytoma) in Dogs.” Pet Place. (April 30, 2011)

Rest, Joan. “Mast Cell Tumors in Dogs.” Veterinary Cancer Care P.C. Dec. 19, 2008. (April 30, 2011)

Washington State University College of Veterinary Medicine. “Canine Mast Cell Tumors.” Jan. 27, 2009. (April 30, 2011)

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