Mast Cell Tumors in Dogs

6 min read
6 min read

Updated - Aug 9th, 2022

Whether your pup has just been diagnosed with a mast cell tumor, or you suspect they might have one, we’re here to help.

Mast cell tumors (or MCTs) are a type of skin tumor in dogs. Though a cancer diagnosis can be scary and certainly shouldn’t be taken lightly, in many cases, MCTs are easily treatable. Here’s what you need to know about symptoms, causes, and treatment of mast cell tumors in dogs.


Mast cell tumors most commonly take the form of a raised bump or lump on the skin, though their appearance may vary widely. It is typically either ulcerated or hairy, and depending on the internal chemistry of the tumor, it may grow or shrink. If you spot a growth on your dog, it’s important not to touch or mess around with it. The mast cells in the tumor are active, which means a process called degranulation can occur. This in an allergic reaction that releases chemicals into the bloodstream that may cause side effects such as ulcers, vomiting, loss of appetite, lethargy, and black stool



  • Mast cell tumors are commonly diagnosed with fine needle aspiration (FNA) or a tissue biopsy.
  • Other diagnostic tools may be used to identify possible metastasis, including blood and urine samples, abdominal ultrasound, chest radiographs, and CT scans. 


Although MCTs are serious, they are also one of the most treatable cancers. At higher grades, successful treatment becomes more difficult, but lower grades of MCT can be easily treated with surgery to excise the tumor. As the severity of the case increases, chemotherapy becomes a necessary supplement. MCTs are highly sensitive to radiation therapy, so this treatment can offer a high success rate in curing the condition.

After diagnosis, your vet or veterinary oncologist may recommend a prognostic panel on a sample, providing more information to determine the likely outlook for the disease. The prognosis is graded from I to III in terms of the tumor’s aggression and the likelihood of metastasis, with grade I being least aggressive and grade III tumors being most aggressive. The grade of the prognosis will affect which treatment options your vet recommends.

Your treatment plan is based on your prognosis, and your prognosis depends on a number of factors, including:

  • Your dog’s breed (whether they belong to a more high-risk breed, like bulldogs)
  • Where the MCT is located (if it’s near a mucous membrane, that’s less favorable)
  • The number of cells actively replicating in the sample.

Surgical excision is the most common treatment for MCTs. In order to ensure all cancerous cells are removed, there tends to be wide surgical margins (i.e., the cuts will be wider than the apparent area of growth). The excised tumor will be sent to a histopathology lab for further tests.

Certain drugs are being developed to target the proteins responsible for MCT growth. These drugs are called tyrosine kinase inhibitors, or TKIs, and they specifically target cells with KIT mutations. This may provide an alternative to surgery in cases where surgical excision is not possible. 

Recovery and care

A combination of surgical excision and chemotherapy is usually successful in curing low-grade tumors and mid-grade MCTs. High-grade tumors, however, have a more complex prognosis. Even with treatment, dog survival times may only amount to a few months. Though no one likes to think about it, in these cases, palliative care may be the best option. In moments like these, it’s important to lean on your vet for support and advice.

In order to reduce some of the effects of degranulation, your vet may prescribe antihistamines for your dog. These prevent the symptoms described above, including ulcers and nausea. This can play a role in palliative care, but it’s also a normal part of surgical preparation.


If you notice any bump or swelling on your pet, you should bring them into the vet’s office. Even if the growth turns out to be benign, it’s better to be safe than sorry.

What to expect at the vet’s office

Your vet will likely carry out some of the tests to determine whether the growth is benign or malignant. They may consult a veterinary oncologist (an expert in pet cancers) to assist in their diagnosis and development of treatment options.

While most vets still use the grade I to grade III system mentioned above, some use a two-grade system in which tumors are separated into high-grade and low-grade. This gives more discretion to the vet in determining a prognosis.

The bottom line

Identification is the first step in treating mast cell tumors. Keep a close eye on your dog’s skin, carefully monitoring for any changes. Take them to the vet right away if you notice any unusual bumps or swelling. The sooner you intervene with veterinary care, the better.


How can I spot a canine mast cell tumor?

Bathing your dog or even giving them belly scratches and cuddles is a good opportunity to look for lumps and bumps. If anything looks suspicious, bring it to the attention of your veterinarian. It’s better to identify MCTs when they’re small – so even if you think it might just be a bug bite, it never hurts to get a professional opinion.

How much does treating canine mast cell tumors usually cost?

Costs can range from hundreds to thousands of dollars for MCT surgery and post-operative care. However, you may be able to get reimbursed for diagnostics and treatment through pet insurance if your plan lists MCTs as an eligible condition.

Are mast cell tumors in dogs covered by pet insurance?

Pet insurance can help you pay for unexpected accidents and illnesses by reimbursing you for eligible vet bills. Depending on what pet insurance plan you have, you may get help covering eligible expenses associated with MCT diagnosis and treatment, helping you focus more on care and less on cost.

Did you know?

  • MCTs are often called “great pretenders” because they are easily mistaken for more benign ailments like insect bites, warts, and allergic reactions.
  • You should never touch or manipulate an MCT growth on your dog, as this can provoke an allergic reaction. Similarly, you should keep your dog from biting or scratching the growth.
  • Although MCTs most commonly affect the skin, they may also occur in subcutaneous forms, affecting the spleen, liver, intestine, or bone marrow. 
  • Pumpkin Dog Insurance plans cover 90% of eligible vet visits – helping you provide your pooch with the best possible care if accidents and illnesses arise. Get a free quote today!

George Menz

George is a copywriter who has lived alongside cats his entire life.
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