What’s a Mast Cell Tumor on a Dog?

What is a mast cell tumor on a dog?

It’s normal for dogs to get lumps or bumps on their bodies from time to time. Most will be nothing to worry about but a mast cell tumor (MCT) does not fall into that category.

MCTs are the most common type of skin cancer found in dogs. They’re adept at mimicking other skin conditions and that can make it almost impossible to identify a mast cell tumor simply by looking at it.

Read on for the lowdown on the causes, symptoms, and treatment for these kinds of tumors in dogs.

What is a Mast Cell Tumor?

Mast cells are white blood cells that form part of the immune system. They play an integral role in the response to allergies.  

Mast cells become cancerous when they start dividing abnormally and grow into tumors. MCTs can come in any shape, firmness, size, or location. More often than not, they are firm, slow-growing masses of the skin. Most dogs with the condition will only develop one tumor. Occasionally, MCTs can lead to serious allergic reactions in dogs. 

They are more common in middle-aged dogs. Particular breeds are more prone to MCTs. These include:

  • Boxers, Pugs, and Bulldogs
  • Pit Bulls and Boston Terriers
  • Retrievers, Rhodesian Ridgebacks, Weimaraners, and Schnauzers 

What Causes This Type of Cancer?

It’s not clear why certain dogs may develop MCTs – or any other cancer. Very few cancers have one single cause. Most appear to be the result of a complicated mixture of risk factors related to the environment, genetics, and heredity. 

We know that several genetic mutations play a part in the development of MCTs. Because it can be so tricky to tell MCTs from other benign conditions, you should always seek the advice of a vet if you suspect your dog may have an MCT.

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Signs to Watch for 

Clinicians have often referred to MCTs as “the great pretenders.” This is because they can look like a wart, insect bite, allergic reaction, or other less severe kinds of tumor. They can also change their size and shape slowly, rapidly, or sometimes not all.

MCTs may not lead to any symptoms. So, you should contact your vet if you notice:

  • A new skin mass appearing
  • A previous mass that alters size or color 
  • An allergic reaction or hive that you can’t explain

Some MCTs may be small and easily movable just under the skin with little swelling. Aggressive tumors can crop up as larger, hairless sores. 

If a tumor gets bumped or irritated, it might go through a process known as “degranulation.” The tumor would then release all its inflammatory material in one go. 

Given how reactive MCT is, you should avoid feeling or manipulating the tumor in order to prevent triggering degranulation. 

Degranulation can cause symptoms such as swelling and redness in the affected area as well:

Making an MCT Diagnosis

Your vet will typically initially try to identify mast cell tumors on your dog through fine needle aspiration (FNA). This is a simple procedure and would normally not require an anesthetic. A needle placed in the mass will suck out some tissue – which the vet can then examine under a standard microscope. In some cases, this can be all that’s needed to diagnose a mast cell tumor.

However, sometimes an FNA is not conclusive. In this case, usually the lump is removed and sent to a laboratory for a more extensive investigation. This does two things: first, it confirms the diagnosis of an MCT. And second – if the lump is an MCT – is will give information about what stage it is and how aggressive (spreading) the MCT is. Low-grade tumors tend to be less aggressive in contrast to their high-grade tumor counterparts.

How Does This Cancer Progress?

The outlook for a dog with an MCT tends to be less favorable if:

  • The dog belongs to one of the susceptible breeds
  • The MCT lies at a junction where the skin meets mucous membranes e.g. the gums
  • The quantity of cells actively replicating is high

Mast cell tumors do not typically cause pain unless your dog experiences symptoms from a tumor-induced allergic reaction. 

Treatments for Mast Cell Tumors on a Dog

In most cases – if possible – the first step is surgical removal.

The recommended treatments vary between low and high-grade tumors. More than three-quarters of mast cell tumors will be lower grade and unlikely to come back after surgery. 

High-grade MCT’s can be very aggressive. They can spread both locally (around the site of the tumor), but also to distant internal organs and lymph nodes. In these cases, your vet may recommend further testing including lymph node aspirates and chest x-rays. 

The preferred course of treatment may then be chemotherapy, radiation therapy, or other treatments. A veterinary oncologist would be the best person to consult for this.

Recovery from Mast Cell Tumors

Dogs will need around 2 weeks of rest to recover from the surgical removal of a low-grade mast cell tumor. Your vet will also typically prescribe pain medications and antihistamines. 

They may also recommend that your dog wears an e-collar to prevent them from licking and irritating the affected area. In most cases, dogs will then continue to live their natural lifespan. In effect, surgical removal can be a complete cure.

It is important to keep an eye on the area where the MCT first appeared for a few months after surgery. Very occasionally you may see a tumor come back but this is highly unlikely in the case of most low-grade tumors. 

In cases of high-grade tumors, recovery after surgery will be the same. However, additional treatments like radiation or chemotherapy may have an impact.

Check Any Bumps or Lumps Out With a Vet

It’s almost impossible to diagnose an MCT in dogs by simply looking at a lump or bump. You should seek the advice of a vet if you become worried about a new skin mass or an older one that changes color or size.

We have a team of highly-qualified vets available to help and offer advice. Book an online consultation today for extra peace of mind.

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