Mast Cell Tumors In Dogs: How Concerning Are They?

November 19th, 2019. Last Updated September 10th, 2020

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Mast cell tumors can be a real unpleasant surprise for any dog owner. Learning that your dog has cancer is always a tough blow.

We had our scare when Yuna was diagnosed with a mast cell tumor about a month ago, in mid-October of 2019.

READ: Life With Yuna: Mast Cell Cancer Survivor

Since mast cell tumors are, in fact, a form of cancer, this is no small matter!

We’ll go over a quick overview of what mast cell tumors are, what you can do about it, and how concerned you should be.

Because even though we hope our dogs are forever healthy and wagging their tails with delight, health issues are an unfortunate reality. It’s best to be well-informed of them during or even before your dog gets sick.

Let’s begin by asking the 5 big questions: the how, what, when, where, and why of mast cell tumors.

What Are Mast Cell Tumors?

Mast cell tumors (MCT) are a type of cancer of mast cells (white blood cells), which play an important role in the immune system.

Mast cells patrol your dog’s body and rush over to battle allergens, infections, or areas of inflammation.

When there’s uncontrolled spread and growth of mutated mast cells, they become an MCT. This is cancer.

How Do Mast Cell Tumors Look?

In the beginning stages, MCTs usually appear as solitary lumps, either on or just under the skin.

The actual shape and appearance of an MCT can vary drastically from dog to dog.

They have been described as being as small as a pea to as large as a softball.

A single MCT can also vary in size over time. One strange characteristic of MCTs is that they can grow and shrink very rapidly, and often appear red, thick, or irritated.

Where Are Mast Cell Tumors Typically Found?

You should do a thorough check of your dog’s skin. MCTs are most commonly found on the trunk (42-65%), limbs (22-43%) and head and neck area (10-14%) of dogs.

If the MCT is dealt with early, the area of impact usually doesn’t extend beyond the skin site.

However, if the MCT has spread to internal organs, they can spread to the spleen, liver, lymph nodes, lungs, or bone marrow. There is also the chance of multiple affected skin sites.

When Do Mast Cell Tumors Typically Begin To Form?

According to PetMD, the mean age when dogs develop MCTs is about eight years old.

That doesn’t guarantee your young puppy is free from MCTs. It’s possible they can form in dogs less than one year of age.

Why Do Mast Cell Tumors Form?

In general, the root cause of MCTs is still largely unknown.

We do know that genetics have proven to play a role. Certain breeds are more susceptible to MCTs: they include Boxers, Boston Terriers, Beagles, Schnauzers, Retrievers, Bulldogs, and Pugs.

A dog sitting at a park with her head down, as if she's guilty of something.

Does My Dog Have A Mast Cell Tumor?

Go ahead, stop reading this article and do a head to tail check on your dog now. You should be looking for any irregular looking skin masses on your dog.

These lumps, as mentioned before, can grow and shrink rapidly depending on how benign or aggressive the tumor is.

If you’re unsure of whether or not some lump you see is an MCT or not, take note of whether you notice it growing or shrinking over the next few days.

In addition, these lumps are also quite itchy for your pup. If you notice your dog deliberately pawing at or scratching the lump, it could confirm an MCT.

Of course, any abnormal lumps should be looked at by a vet. If not an MCT, it could be another disease or virus that is equally dangerous if ignored.

If you do plan to see the vet about a lump, most vets will want to know the history of the lump before taking further steps–when you noticed it, any changing behavior in your dog as a result of it, etc.

An infographic outlining what mast cell tumors are in dogs: what, where, how, and why.

Typical Treatment For Mast Cell Tumors

Under most circumstances, surgical removal of the mass is almost always necessary. A biospy on the mass will reveal whether the mass is a mast cell tumor.

Before surgery, some vets will choose to sample the mass. This involves using a needle to obtain some cells for examination under a microscope.

If suitable, some vets will recommend removing the mass right away. This is a full surgical procedure that may involve placing the patient on antihistamines (Benadryl) and antacids (Pepcid AC or Prilosec). Ask about whether these are necessary before your vet takes your dog back for the procedure just so there are no surprises when you get the final bill.

The procedure will also require full sedation.

The surgery itself can usually be performed relatively quickly for reasonably-sized tumors. If your dog went into surgery in the morning, they should be stable and ready to go home in the evening.

Post Treatment Steps

After the surgery, your dog will usually be placed in a cone. Transitioning into life with your dog in the cone can be difficult for both of you. Check out our article below for some pointers.

READ: How To Make The Dog Cone More Comfortable

The removed skin mass will be sent to a pathologist to conduct a biopsy. Results will typically come in within a few days to further understand the removed mass, and how severe the MCT is.

Depending on the surgery, there may or may not be additional cancerous cells remaining. You may have to conduct a second surgery to remove a wider area of skin, as was the case for Yuna.

In addition, your vet may check on whether or not the MCT has spread internally. An X-ray of the lungs is standard, as that is one of the first places mutated mast cells go to.

Other precautionary steps can include blood tests, an abdominal ultrasound, and bone marrow aspiration.

For more severe MCTs, chemotherapy or radiation therapy may be recommended. Let’s talk some more on how MCTs are graded for severity.

Severity of MCTs: Two Grading Systems

MCTs are graded on two scales.

Patnaik System

First, there’s the traditional Patnaik system. Here, there are three distinct grades indicating severity, with Grade 1 being the least severe and aggressive, and Grade 3 being the most severe and aggressive.

Grade 1 typically means that there’s a good chance the MCT won’t recur if completely removed.

Grade 2 means the MCT is more likely to disseminate to other parts of your dog’s body compared to Grade 1.

Grade 3 means it’s extremely likely to recur, and the MCT may have already made it into the skin and other tissues.

Kiupel System

Secondly, there’s the newer Kiupel system. Many vets have adopted this new approach over the previous “gold standard” Patnaik system. Here, there are simply two grades: low-grade and high-grade MCTs.

A study found that they correspond to the Patnaik system in the following way:

All Grade 1 MCTs in the Patnaik system were low-grade in the Kiupel system.

All Grade 3 MCTs in the Patnaik system were high-grade in the Kiupel system.

85.6% of Grade 2 MCTs in the Patnaik system were low-grade in the Kiupel system.

14.4% of Grade 2 MCTs in the Patnaik system were high-grade in the Kiupel system.

The biopsy report returned from the pathologist will often give both Patnaik and Kiupel grades for the MCT.

Survival Chances

The reason we want to know the grades of the MCT is to determine the appropriate next steps for treatment.

But it also tells the survival chances of your pup after having endured the MCT. It’s a tough subject to talk about for sure.

Let’s begin by discussing the “50/50” mark. In the Patnaik system, dogs with Grade 2 tumors usually have around a 50/50 chance of a 5-year survival.

In Yuna’s specific report from IDEXX, the notes mention that 47% of dogs survived a Grade 2 (Patnaik) tumor for 1500 days or more.

Also from the report, dogs with low-grade MCTs (Kiupel) had a median survival time of “over two years” and only 5% of patients died with additional MCT-related diseases. Yes, “over two years” is a rather large time frame.

1 Year Survival Statistics

Using the Patnaik and Kiupel grades in conjunction, a study found the following statistics for 1 year survival odds:

  • The 1 year survival probability of Grade 1 tumors is near 100%.
  • The 1 year survival probability of Grade 2, Low-grade tumors was at 94%.
  • The 1 year survival probability of Grade 2, High-grade tumors was at 46%.
  • The 1 year survival probability of Grade 3 tumors is 16%, with median survival time at around 150 days.
An infographic showing various severities of mast cell tumors and expected survival chances.


Ugh, we just busted out some potentially catastrophic news for some dog owners out there.

Whatever the result of your MCT biopsy, your vet will discuss with you the best path forward to ensure highest chances of survival for your dog.

What’s important here is to realize that it really depends on how early you can detect the tumor for the best prognosis.

Even the smallest lump needs to be examined. Don’t underestimate any of them.

I initially thought Yuna’s lump was just a pimple. Turned out it was a mast cell tumor. We will write a more complete article about our experience with MCTs soon.

We sincerely hope none of this ever happens to your fur kid. And for any dog currently going through this, we hope you have the best possible outcome.

A dog standing on a bed of red, white, and pink leaves, matching the Minnie Mouse bandana she is wearing.

The fact remains that it never hurts to be informed!

That’s why you should follow Yuna’s Instagram and Pinterest for daily updates and more free doggy health tips just like this article. Feel free to reach out to us there!

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