Mast Cell Tumors in Dogs: What You Need to Know

dog mast cell tumors broomfield, co
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New or unknown bumps and lumps on your dog can be concerning for any owner. Usually these lumps are benign, but some could be malignant like mast cell tumors.

If you notice any new bumps on your dog, take them to your vet for a proper diagnosis. However, if you’re interested in learning about dog mast cell tumors, how veterinarians diagnose them, and how they’re treated, read our Broomfield, CO, animal hospital’s article below.

What is a Dog Mast Cell Tumor?

A mast cell tumor is a type of tumor consisting of mast cells, which are a type of white blood cell found in connective tissue all throughout the body—especially under the skin, near blood and lymph vessels, in nerves, lungs, and intestines.

Mast cells are part of the immune system and play a role in allergic responses. When they’re exposed to allergens, chemical compounds called degranulation are released. One of these compounds is called histamine, which is known to cause itchiness, sneezing, and runny eyes. When these compounds are released in excessive amounts, the results can be deadly if anaphylaxis occurs.

Mast cell tumors have classically been called, “the great pretenders,” because they often mimic or resemble an insect bite, wart, allergic reactions, or less serious types of skin tumors.

Therefore, any abnormalities on your dog’s skin should be evaluated by a veterinarian.

How Does a Dog Develop Mast Cell Tumors?

It is unknown why particular dogs develop mast cell tumors (or any other type of cancer). However, most effected dogs have mixed risk factors such as genetic mutations and environmental surroundings. Any breed can get mast cell tumors, but Boxers, Bull Terriers, Boston Terriers, and Labrador Retrievers are particularly susceptible.

Other known factors are food allergies, chronic inflammation, or gut issues.


Here are the most common symptoms of mast cell tumors in dogs:

  • Bumps on the skin
  • Swollen or irritated skin
  • Ulcers in the stomach or intestines
  • Vomiting
  • Loss of appetite
  • Lethargy
  • Melena (black, tarry stools associated with bleeding)

It is uncommon, but some dogs who have a mast cell tumor can experience anaphylaxis. Another less common symptom includes mast cell tumors of the skin spreading to the internal organs, causing enlargement of the lymph nodes, spleen, and liver. In addition, fluid build-up can occur in the abdomen, which will cause the belly to be rounded or swollen.


If your veterinarian suspects your dog has a mast cell tumor, they will likely diagnose your dog using a fine needle aspiration (FNA) and a prognostic panel.


A fine needle aspiration involves taking a small needle with a syringe and suctioning a sample of cells from the tumor. The cells are then placed on a microscope slide.

A veterinary pathologist will examine the sample under a microscope and determine if any cells look abnormal.


Once a diagnosis has been made, your veterinarian or veterinarian oncologist may recommend a prognostic panel on a tissue sample. This can determine the genetic makeup and abnormalities that provide valuable information to determine your dog’s prognosis.


Mast cell tumors are one of the most treatable types of cancer, despite its range in behavior and prognoses. However, higher-grade tumors are more difficult to treat than those that are of a lower grade.


For tumors that are lower grade and show no evidence of spread, surgery is almost always the best option. Chemotherapy is typically not required after the surgery is performed.


Even without the evidence of spread when it comes to higher-grade tumors, a combination of surgery and chemotherapy is often recommended.


However, if the tumors of any grade are in a spot that is unsuitable for removal via surgery or if the surgical removal is incomplete, radiation therapy may be recommended.


Medication is still currently being developed to target cancer treatments. However, medication may serve as a treatment option for dogs with non-surgical mast cell tumors or recurrent tumors that have failed to respond to other therapies.

Your veterinarian will determine the best course of treatment for your dog.


Mast cell tumors are incredibly reactive, so owners should avoid feeling or manipulating tumors.

In addition, your dog should not chew, lick, scratch, or otherwise access the tumor because that could cause further itchiness, swelling, discomfort, or bleeding. To prevent your dog’s access to the tumor, your vet may recommend your dog wear a collar or cone. Dogs with mast cell tumors may also need to be isolated from other animals.


Mast cell tumors, when caught early, are typically easy to treat through surgical intervention. However, the tumors can present themselves as several other ailments, so any change in your dog’s skin should be addressed with your vet.

If you believe your dog has mast cell tumors, bring them in for an exam at our Broomfield, CO, animal hospital. To schedule an appointment, give us a call at (303) 469-5363.

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