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A Veterinarian Explains What Your Dog’s Mast Cell Tumor Risk Means

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As part of our genetic health screening, Embark dog DNA tests can determine if some dogs are at increased risk of developing mast cell tumors (MCTs). This risk is based on genetic breed ancestry and other factors. This model offers a new way to estimate relative risk for MCTs, especially for mixed-breed dogs.

We know that learning about your dog’s risk for mast cell tumors can raise a lot of questions. We spoke with Embark veterinarian Kari Cueva, DVM about what your dog’s mast cell tumor risk result means and how you can use it.

My dog’s Embark results show an increased risk of developing MCT. Should I worry?

In short, no—don’t worry. Remember that a risk estimate is not a diagnosis. These results are intended to help inform pet owners and veterinarians, so that they can proactively monitor dogs who are at higher risk. Monitoring can lead to earlier detection and improved treatment outcomes.

Mast cell tumors are the most common malignant skin tumor in dogs, which means that veterinarians are typically very familiar with how to diagnose and treat MCTs. Additionally, most MCTs (more than 80%) are of low or intermediate grade and often curable with surgery alone.

It is important to keep in mind that while Embark’s model uses breed ancestry and other genetic factors to predict MCT risk, there are likely many other factors, both known and unknown, that increase or decrease a dog’s risk of developing MCT.

Your dog’s Embark results can help you be proactive in their care, which can include something as easy and beneficial as petting your dog more. Here, we’ll explain how you can use this risk estimate as a tool to support your dog’s health and catch concerns earlier, so your veterinarian can treat them early.

What does my dog’s risk mean?

While mast cell tumors can affect any dog, some breeds are more susceptible than others. 

The scientific literature so far characterizes increased MCT risk in certain breeds, usually studied only in purebred (or single-breed) dogs. How to apply that risk assessment to mixed-breed dogs (who have ancestry in the breeds studied) is less straightforward. Plus, breed ancestry may not be apparent just by looking at a dog’s outward appearance, which can make it tricky to know the potential risk.

The Embark algorithm combines your dog’s breed, sex, and other genetic factors to provide their individualized risk score. This ancestry-based algorithm is a completely new approach to predicting disease, powered by Embark Research and the health data that customers provide to us.

Our risk model includes the following breeds:

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

While the breeds above are the ones 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.

Why does my dog’s risk for mast cell tumors matter?

No matter what the number associated with the increased risk is (large or small), there are noninvasive, non-painful, and even mutually beneficial ways that you and your veterinarian can discuss to monitor your dog. The results are intended to help you better note signs that can aid in early detection and improved treatment outcomes.

How do veterinarians use MCT risk in a dog’s care plan?

The Embark model is a novel approach, so we can’t comment on how vets will use this result just yet. However, in breeds that were previously known to be at an increased risk, veterinarians may recommend increased vigilance in at-home lump checks, more frequent veterinary visits, more detailed lump mapping, and/or earlier diagnostic intervention (like a fine needle aspirate).

What should I do if my dog has a higher risk for mast cell tumors?

“The best way to catch mast cell tumors early is through monitoring,” says Dr. Cueva. Add regular body checks into your dog’s routine to check for new lumps and bumps and monitor old ones. These at-home body checks are quick, painless, and just as easy as petting your dog.

Keep in mind that there are some bumps on your dog’s body that are likely normal, so your veterinarian can give you the best guidance in person about doing a physical exam for your individual dog.

In general, here’s how to perform an at-home physical exam and check your dog for lumps and bumps: 

  1. Place a flat hand against your dog’s body.
  2. Run your hand across your dog’s body and feel for any masses under, on, or within the skin. Make sure you cover their entire body, including areas that might be hard to reach, like their head, ears, and feet. If your dog has a lot of hair, make sure you can feel their skin underneath. Lump checks may be easier to do when your dog is wet, like during a bath.
  3. If you can do so safely, look inside their mouth and check for any new bumps there, too.
  4. If your dog is sensitive to touch, you may only be able to do a visual inspection of some areas, such as their feet or near their genitals. Remember, you don’t have to examine their whole body all at once. If you or your dog need a break, take one.
  5. If you notice a small mass, it may be difficult for you or your vet to find it later. You can use a skin-safe marker to circle the mass or take photos or videos of the area for reference.
  6. Share your dog’s Embark results with your veterinarian by sending them through your dog’s Embark profile.

What should I do if I notice something unusual?

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

Because MCTs can be itchy and irritating, your dog may bite, lick, or scratch at the tumor, which causes mast cells to release their contents, including histamine. It might be a good idea to have your dog wear an Elizabethan collar (E-collar) until your appointment to prevent them from aggravating the tumor.

What should I expect at the veterinary appointment?

“If you notice a new lump or bump and bring your dog to the vet, you’ve already taken the right next steps,” says Dr. Cueva. From there, to diagnose a mast cell tumor accurately, veterinarians usually use a simple fine needle aspirate (FNA) of the tumor in most cases. 

Determining the grade (and therefore prognosis) of a mast cell tumor can’t be done with the FNA. It requires a tissue sample. That tissue sample usually involves taking a small piece of the tumor (called an “incisional biopsy”) or surgically removing as much of the visible tumor as possible (called an “excisional biopsy”).

A pathologist then evaluates the tissue, which means looking at the sample under a microscope, evaluating characteristics of the tumor, and determining the grade of the tumor. The grade then tells us about the potential for the tumor to spread, prognosis, and necessary follow-up treatment options. Your veterinarian or the pathologist may also recommend genetic analysis of the tumor.

The spread of tumor cells (metastasis) happens first at the lymph nodes near the tumor, and then potentially in other areas of the body. Your veterinarian may recommend extra staging tests for your dog to look for any evidence of metastasis. This may include another FNA, this time of the regional lymph nodes or abdominal organs. Your veterinarian might also recommend a basic blood panel, urinalysis, abdominal ultrasound, and/or chest X-rays.

How are mast cell tumors treated?

“Early detection, which typically allows us to address tumors when they are small and localized, increases the likelihood that a treatment is successful and the tumor can be cured,” says Dr. Cueva.

Once a dog is diagnosed, the preferred treatment of discrete MCTs is surgical removal. Before surgery, your veterinarian may recommend medical management to help reduce inflammation and counter the side effects of MCTs. Your veterinarian may also recommend a consultation with a veterinary specialist in oncology or surgery.

After surgery, the most important factors when deciding whether additional treatment is needed include:

  • Tumor grade (how much the tumor has invaded the surrounding skin and how quickly it is growing)
  • Completeness of surgical margins (the area of normal tissue removed around the tumor)
  • Stage of the tumor (if the tumor has spread to other parts of the body)

Some cases might warrant radiation and chemotherapy after surgery. Your veterinarian may also consider a second surgery, if the surgical margins are not clean. Some novel therapies, including oral or injectable medications, are also available for treating MCTs.

Should I update my dog’s Embark profile?

It’s helpful for the Embark research team to know if your dog has been diagnosed with a mast cell tumor. You can let us know by filling out the Annual Health Survey and Common Cancers Survey in your dog’s Embark account and noting an MCT or any other diagnoses.

Your feedback can help us improve and expand our genetic risk estimates for dogs everywhere. Our research is powered by customers like you—we thank you for your help!

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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