In this article
- What causes mast cell tumors in dogs?
- Common signs and symptoms of mast cell tumors in dogs
- Diagnosing mast cell tumors in dogs
- Prognosis and Treatment of mast cell tumors in dogs
- Summary of mast cell tumors in dogs
Senior Pet Care: A Comprehensive Guide to Supporting Your Aging CompanionWhat are mast cell tumors in dogs?
What are mast cell tumors in dogs?
Dr. Gary Hsia
February 06, 2025
A small lump on your dog could mean more than you think. Mast cell tumors, the most common skin cancer in dogs, can vary in size and severity. Early detection is key—schedule a vet check today for peace of mind and your pup’s health!
Mast cell tumors (MCT) are a type of tumor that originate from mast cells that have grown in abnormal size and number. Mast cells play an important part of a dog’s immune system, helping to defend against allergic and parasitic infections, as well as aid in wound healing and tissue repair. Mast cells tumors are primarily found in the skin, but can also affect the spleen, liver, digestive tract and bone marrow.
Cutaneous mast cell tumors are those that originate in the skin, and is the most common type of skin cancer in dogs. They can vary greatly in their size, shape and appearance. They usually present as a single, solitary tumor but can also occur as multiple tumors. Therefore it cannot be diagnosed purely by visual examination and your veterinarian may perform a number of tests to diagnose the disease, most commonly a fine needle aspirate and cytology of the tumor in question.
What causes mast cell tumors in dogs?
Unfortunately, the exact underlying cause of MCTs in dogs is unknown however there are some environmental and genetic risk factors. There is a known genetic mutation of the KIT protein that is involved in cellular replication. There also seems to be an age and breed predisposition.
MCTs are most commonly found in older dogs around 8-9 years old. MCTs can be found in any breed dog, but seem to be most common in:
• Boxers
• Boston Terriers
• Bulldogs
• Pitbull Terriers
• Labrador Retrievers
•Rhodesian Ridgebacks
Common signs and symptoms of mast cell tumors in dogs
Mast cell tumors usually present anywhere on the body, as a raised lump or nodule on the skin or below. It presents in various shapes and sizes, from smooth to ulcerated to wart-like. Due to the variation in size and location, many different symptoms may be seen.
• Growth or a new tumor
• Changes in size of a tumor
• Redness, swelling and inflammation of the tumor
• Itchiness/ pain/ excessive licking at the mass. Especially on the extremities.
• Enlarged lymph nodes near the tumor
Common symptoms of general or metastasized MCT:
• Lethargy
• Vomiting/ diarrhea
• Loss of appetite and weight loss
• Enlarged liver and spleen (where MCTs most commonly metastasized)
Diagnosing mast cell tumors in dogs
If you find a lump or abnormality on your dog’s skin, you should contact your veterinarian for an examination. MCTs can often be mistaken for less serious skin conditions such as insect bites, foxtails, warts or allergic reactions, but can be very serious and should not be ignored.
Initial evaluation typically involves obtaining a fine needle aspirate or biopsy of the suspicious mass. Fine needle aspiration (FNA) involves your veterinarian taking a small needle with a syringe and poking the tumor to try and suction out cells from the tumor. Those cells are examined under a microscope to determine the presence of mast cells. The FNA method, while less invasive and usually less expensive, may not always yield definitive results. Another method used is called a biopsy, where your veterinarian takes a tissue sample of the tumor for evaluation.
Prognosis and Treatment of mast cell tumors in dogs
The prognosis and treatment options for MCTs vary greatly based on their grade and staging. Once the tumor is biopsied, the pathologist can determine the grade of the tumor which looks at how aggressive the tumor is. Low grade tumors are less likely to spread or return, while high grade tumors are more likely to metastasize and grow back.
Staging of the tumor is also important to determine if the tumor has spread from its original location to other parts of the body. It is usually done with full body x-rays and ultrasound, It can vary from stage 1 with no spread, to stage 4 where it has metastasized to the lymph nodes, spleen and liver.
In general, tumors that are low grade with complete surgical excision have the best prognosis with survival times over two years, compared to high-grade tumors that have spread to lymph nodes, gastrointestinal tract, spleen or liver have a poor prognosis with survival times less than four months. Dogs that have had previous MCTs are at greater risk for developing additional new mast cell tumors.
It is recommended to visit a veterinary oncologist to determine the best treatment options for your dog. Treatments can include surgery, chemotherapy, radiation therapy and targeted immunotherapy. Complete surgical excision of the tumor is the best option, and may be curative for dogs with low grade tumors. However, in higher-grade tumors, a combination of surgery and chemotherapy is usually recommended. Radiation therapy is sometimes an option if the MCT is in a location where surgery cannot be performed or used to eliminate any remaining cancer cells from an incomplete surgery. Some newer immunotherapies such as Stelfonta, Gilvetmab, Palladia have been developed to specifically target MCTs and may be helpful in certain scenarios such as non surgical tumors..
Your veterinarian may also recommend a series of other medications such as steroids, anti-histamines (benadryl), pain medications, anti-nausea medications and antacids to help with the symptoms of MCTs and as palliative treatment to extend your dog's quality of life.
Summary of mast cell tumors in dogs
Mast Cell Tumors are the most common skin cancer in dogs. It can present in a number of appearances from smooth to raised to ulcerated lumps on the skin. Due to its varied appearance, it is recommended you consult your veterinarian if you notice any new or unusual lumps on your dog. Prognosis and treatment is highly dependent on grading and staging of the tumor but early detection and treatment, especially when the tumor is small, will improve the chances of the best outcome.
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