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Mast Cell Tumors in Dogs

By Sarah Hilario, DVM

Every owner should be knowledgeable about mast cell tumors (MCTs) because they are the most common type of skin cancer in dogs.  Mast cells are a normal part of the body’s immune system and are commonly found throughout the layers of skin.  Genetics plays a major role in the formation of a MCT.  Any age or breed can be affected, but higher risk breeds include boxers, boston terriers, bulldogs, pugs and labrador and golden retrievers. Dogs eight years and older are also more likely to develop them.  Mast cell tumors vary in appearance.   They can resemble a small wart like lesion, appear as a circular ulcerated lump on the skin, or even grow underneath the skin in an area called the subcutaneous layer. 

If you notice any lump on your dog bring it to your veterinarian’s attention immediately.  A simple test called a fine needle aspiration can be easily performed to determine if your pet has a MCT. Unfortunately, the fine needle aspiration cannot determine the grade of the MCT.  Therefore, surgery is required to remove the tumor as well as healthy tissue around the tumor to send out for analysis. Mast cell tumors are graded from 1 (low) to 3 (high) depending on how aggressive the cancer is.  Grade 1 tumors act benignly and typically they only require surgical removal of the lump.  Grade 3 tumors can be highly malignant and spread to other areas in the body including the lymph nodes, spleen, and liver.  High grade MCTs commonly require additional treatment after surgery and carry a poorer prognosis.  If the tumor cells extend to the edge of the sample then additional surgery, radiation therapy, or chemotherapy are required. 

All lumps on your dog should be tested as soon as possible and if a MCT is diagnosed an individual treatment plan based on your pet’s needs will be created.  Be a proactive canine parent, and look and feel for lumps and bumps as you lovingly give your dog a relaxing massage, or during a weekly coat brushing session.