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Mast Cell Tumors in Dogs


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Knowing how to recognize common signs of mast cell tumors in dogs can help you catch them early. At Embark, we’re committed to improving the life and longevity of all dogs by providing our customers with information about their dogs’ health. 

With that goal in mind, we now offer a genetic risk estimate that indicates whether a dog has an above-average risk for developing this condition. This estimate is based on a dog’s genetic ancestry and comes with expert advice about how to use this information to be proactive in your dog’s care.

Here, we’ll explain what mast cell tumors are, how genetics and breed ancestry affect our risk model, and the steps you can take if you know your dog’s risk.

What are mast cell tumors in dogs?

Mast cell tumors (MCT) are the most common type of malignant skin tumor found in dogs. They represent 11–21% of all skin tumors diagnosed in dogs

Mast cells are a type of white blood cell, a natural part of the body’s defense against parasites. When working normally, they are an important part of your dog’s immune response. However, sometimes, these mast cells can join together and form masses in or under the skin. These masses are typically palpable, meaning you can feel them with your hand. They are usually found on a dog’s head, neck, limbs, or trunk. MCTs can sometimes affect internal organs, too. In those locations, they are typically not palpable.

If caught early, mast cell tumors are treatable. More than 80% of mast cell tumors are curable by surgery alone.

What are the signs and symptoms of mast cell tumors in dogs?

Dogs with mast cell tumors may show any combination of the following signs:

  • A new mass under, on, or within the skin
  • An existing mass that has changed (in size, color, or hair cover)
  • Swelling, redness, and/or itching of an existing mass
  • A bleeding mass
  • Swelling of the face or hives
  • A mass that gets bigger, then smaller over 24 hours
  • Unexplained appetite loss, vomiting, and/or diarrhea

If you notice any of the above signs, schedule an appointment with your veterinarian.

In addition to knowing the signs to look out for, knowing your dog’s risk for developing mast cell tumors is a key part of management. Using a novel ancestry-based model, we now offer an estimate of genetic risk for MCT for our customers and their dogs.*

How does Embark determine genetic risk for mast cell tumors in dogs?

Powered by Embark Research and our customers, this novel method uses several genetic factors to calculate an estimated risk of mast cell tumors for both single-breed and mixed-breed dogs of specific origin. The ancestry-based risk model combines genetics, breed ancestry, and Embark owner-reported research data to estimate a dog’s relative level of risk for developing MCT.

Our scientific model for MCT risk is unique, offering the first cancer-related risk assessment of its kind from a dog DNA company. It is not a diagnostic test, but rather a predictive tool that can inform how veterinarians and pet owners provide interventional care for dogs who may be at risk of developing MCT in the future.

This MCT risk estimate was initially released as a beta model.* Our team is now working on a full release of this new feature. We will update this article with more information about when the MCT risk estimate will be available for all dogs.

*Applies to test results received after May 15, 2023. Includes the Breed + Health Test, Purebred Test, Breed ID Test with health upgrade, Embark for Breeders, and Embark for Veterinarians.

Which dog breeds are included in the mast cell tumor risk model?

Any dog can develop a mast cell tumor, but some breeds are more susceptible than others. Our MCT risk model factors in ancestry from the following breeds associated with higher risk:

In addition, there are two breeds in our model associated with a lower risk for MCT:

While the breeds above are currently included in our MCT risk model, it’s important to note that risk is not limited to these breeds alone. Dogs with ancestry in other breeds can also develop MCT. Cancer research is an ongoing area of focus at Embark, and we may expand this risk model in the future as we learn more about MCT.

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How are mast cell tumors diagnosed?

In almost all cases, mast cell tumors can be diagnosed accurately with a fine needle aspirate (FNA), a sampling method that uses a thin needle to take a sample of the tumor. Analysis of a larger tissue biopsy is necessary to determine the grade of the tumor, which helps to inform prognosis and treatment options.

Your veterinarian may recommend additional tests, including imaging and a needle aspirate of the lymph nodes and abdominal organs, to determine if the tumor cells have spread. Other tests, like bloodwork and urinalysis, may also be used to check for secondary effects of the tumor spreading or to determine which treatment options might be appropriate.

How are mast cell tumors treated?

If your dog is diagnosed with a mast cell tumor under, in, or on the skin, surgical removal of the tumor is typically the preferred treatment. Your veterinarian can recommend the best course of action for your individual dog.

Mast cell tumors tend to invade the tissues around them, which means that the surgeon needs to remove a wide surgical margin (area of healthy tissue around the tumor) to make sure they catch and remove all the local cancerous cells.

Before surgery, your veterinarian might recommend additional or alternative treatment to help manage the tumor and relieve the associated side effects.

If surgery is not an option, if the tumor is likely to spread, or if the skin tumor is small, your veterinarian may recommend treatments like chemotherapy, radiation therapy, or a drug injection directly into the tumor. Your veterinarian may also recommend a consultation with a veterinary specialist in oncology or surgery.

What to do if your dog is at increased risk for mast cell tumors

Knowing the signs of mast cell tumors and when to seek care can help you prepare for any outcome.

The best way to catch mast cell tumors early is through monitoring. Add regular body checks into your dog’s routine to check for new lumps and bumps and monitor old ones. Make an appointment with your veterinarian if:

  • You notice a new mass in, on, or under their skin
  • An existing mass has changed in size, color, or hair cover
  • A mass is painful or has started bleeding
  • Your dog has signs consistent with an allergic reaction (such as hives)
  • Your dog has undiagnosed gastrointestinal signs like vomiting or diarrhea, especially if they contain red or black (digested) blood

Learn more about the preventive steps you can take with Embark veterinarian Dr. Kari Cueva.

Mimi Padmabandu Contributor

Mimi Padmabandu is a scientific writer and Content Strategy Lead at Embark Veterinary. She has over a decade of experience writing about science and genomics for leading biotechnology companies. She holds a bachelor's degree in Molecular, Cell, and Developmental Biology from UCLA and a master’s degree in Early Modern English Literature from King’s College London.

Read more about Mimi Padmabandu

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