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Mast Cell Tumors in Dogs (Mastocytomas): Symptoms, Diagnosis & Treatment

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Mast Cell Tumors in Dogs (Mastocytomas): Symptoms, Diagnosis & Treatment

Often abbreviated as MCTs, mast cell tumors are one of the more commonly found tumors in dogs. In fact, out of all cases of canine cancer, twenty percent of dogs with cancer are diagnosed with mast cell tumors. The main reason why mast cell tumors are so frequently found in dogs is that these tumors can grow from just about anywhere on your dog's skin. 

Not all mast cell tumors look the same appearance-wise either so they not only grow with ease but they can take on just about any form as well. Adding fuel to the fire, tumors that stem from the rapid growth of mast cells are also incredibly aggressive, meaning they are harder to keep under control. The cancerous cells metastasize very readily, so keeping these tumors under control is key.

Figuring out the location of the tumor is one of the first steps. Bone marrow is a common location for MCTs in dogs, but bone marrow isn’t the sole site of origin. Other locations of origin include the liver, spleen, and gastrointestinal tract of our canine companions. 

The Three Kinds of Mast Cell Tumors

Medical professionals use a grading system to differentiate between mast cell tumors. The grading system places mast cell tumors into one of three categories… 

  • Grade I
  • Grade II
  • Grade III 

Grade I

Grade I refers to benign mast cell tumors. They are the least concerning and the easiest to control of the three grades, though they absolutely require treatment sooner than later. 

Grade II

Grade II is the category of locally aggressive mast cell tumors. They stay local for awhile but this doesn't mean they don't have a high probability of spreading elsewhere. Veterinarians will reference the mitotic index of these tumors to better understand how quickly the cancerous cells will begin multiplying and dividing. 

Grade III

Grade III mast cell tumors have the highest likelihood of spreading throughout the body. Grade III tumors metastasize rapidly. The grade III tumors require immediate intervention because you're working with a shorter time frame. Due to its security, a grade III tumor will often require the introduction of toceranib phosphate as part of the treatment plan.

Even if your dog does not have a tumor of mast cells, it's still beneficial to educate yourself about mast cell lumps because they are such a common form of cancer in dogs. How about we explore the various symptoms of dogs with mast cell tumors so that pet owners can familiarize themselves with the signs of canine mast cell cancer. 

Then, we'll advise you on the various tools used for diagnosing mast cell tumors, followed by an explanation of treatment options for canine mast cell cancer. Let’s get started! 

What Are the Symptoms of Mast Cell Tumors? 

Canine Mast Cell Tumors | Innovet Pet

The warning signs of mast cell tumors in dogs are very eerily similar to the symptoms of cancer in general. Theoretically, it sounds like it would be easier to know that your dog has a mast cell tumor if the side effects of canine mast cell tumors were more unique or distinguished. However, it’s okay that you don’t know the cancer is a mast cell tumor right away. 

The main focus is to seek medical attention for your dog after seeing signs of irregular behavior and recognizing that something is wrong. Don’t worry about trying to figure out what type of cancer your dog has in the moment. Instead, your goal should just be to notice something is wrong and take your dog to the vet for an evaluation. 

Once you have a feeling that your dog is not behaving like normal, schedule an appointment with your dog’s veterinarian. The vet will then be able to evaluate the situation and narrow it down to a specific type of cancer. None of these symptoms are necessarily specific to mast cell tumors, but instead, they are indicative of cancerous cells in general. Always be on the lookout for signs of cancer in dogs so that you can seek out help for your pet sooner than later. 

Some examples of cancer in dogs, including mast cell tumors, are… 

  • Raised bump along the skin 
  • Lymph nodes that are swollen 
  • Gastrointestinal pain and discomfort
  • Sudden unexplained weight gain 
  • Loss of appetite or nausea 
  • Vomiting after eating 
  • Bowel movement issues like diarrhea 
  • Weakness and limp muscles 
  • A cough that won't go away 

Swollen or enlarged lymph nodes are a clear giveaway that cancer is present in your dog’s body. This is true for two main reasons. The first explanation for why lymph nodes swell in the presence of cancer is that the cancerous cells start invading the surrounding lymph nodes. 

Tumor cells often latch onto them and spread throughout the body, which is known as lymph node metastasis. In other cases, the lymph nodes try to combat the cancerous cells, which causes them to swell in response to the cancer.  

Risk Factors of Mast Cell Tumors

Researchers are still trying to figure out what exactly causes canine MCTs. There is an association between MCTs in dogs and the receptor tyrosine kinase, but there is not enough of a connection between receptor tyrosine kinases and MCTs to say RTK causes these tumors in dogs.

All that is known for certain is that some dogs are predisposed to developing mast cell tumors later on in life. Purebred dogs rarely develop mast cell tumors, as this type of canine cancer is more prevalent in mixed breeds. 

Certain dog breeds have a higher likelihood of developing mast cell tumors, including but not limited to... 

  • Beagles 
  • Boxers 
  • Boston Terriers 
  • Bulldogs 
  • Cocker Spaniels 
  • Pitbulls 
  • Retrievers 
  • Rhodesian Ridgebacks 
  • Schnauzers 
  • Sharpeis 
  • Weimaraners

How Are Mast Cell Tumors Diagnosed? 

Symptoms of Mast Cell Tumors in Dogs | Innovet Pet

The most common way of diagnosing mast cell tumors is by conducting a fine needle aspiration. The medical professional will take a needle, gently poke through your dog's skin, and pull a small sample of the mast cell tumor out of your dog. The needle draws the sample of cancerous cells out and into a syringe, which they then take to the lab. 

Placing the sample of cancerous cells onto a slide, the professionals will then view the cells under a microscopic lens to really understand what's going on in your dog's body. Fine needle aspirations are often enough to understand the situation, but sometimes, a more invasive approach is necessary. If the needle aspiration isn't enough, veterinarians will often opt for a biopsy as well. 

Biopsies are more invasive because bigger samples are taken, and typically, dogs are placed under anesthesia during biopsies. Mast cell tumors are often complex enough to warrant a biopsy, so don't feel too worried if your dog's veterinarian orders one. It's not a sign of anything other than the fact that the findings of the needle aspiration were not conclusive. 

To calm any worries you might feel after learning your dog might need a biopsy, keep in mind that mast cell tumors often take the shape of non-cancerous abnormalities, like allergic reactions or bug bites. Since mast cell tumors don't take on a shape that is unique to them, it's easy to mistake mast cell tumors for something else. 

This is why the diagnostic testing options seem so intense, but it's only because the professionals want to ensure that they know what they are dealing with before attempting to treat the situation. Last but not least, a prognostic panel might be ordered when diagnosing mast cell tumors. 

Prognostic panels offer a more in-depth approach to your dog's circumstances. It's a deeper dive into the genetic composition of the concerning lump. Additionally, a prognostic panel can provide insight into the severity of the cancer, which allows medical professionals to form a more well rounded opinion of your dog’s mast cell tumor survival rate.

Treatment Options for Dogs: How To Treat Canine Mast Cell Tumors

There are two major ways that veterinarians go about treating mast cell tumors. It all starts with weighing your dog’s situation against the treatment options and deciding if one form of treatment is enough, or if they should be used in tandem. 

Surgical Removal of Mast Cell Tumors

An abdominal ultrasound will often precede surgical removal of tumors in dogs. Surgical removal is frequently the go-to treatment option with MCTs in dogs when the skin tumor is of a considerable size. Surgical removal is often paired with another treatment option because surgery alone cannot promise to eliminate all cancer cells in your dog’s body. 

Radiation Therapy for Canine Mast Cell Tumors 

Radiation therapy is a key component in the treatment plan of dogs with skin tumors. Radiation therapy can successfully eliminate skin tumors by targeting the cancer cells directly. Radiation therapy utilizes UV lights to kill existing cancer cells and prevent new ones from growing.


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1 comment
  • John Algeo

    Thanks for saving my Lab. She started throwing up after eating, so I started to search around for lumps and found one. Off to the vet ASAP.

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