Mast Cell Tumors in Dogs

Published by Amber LaRock

Updated on

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What are mast cell tumors in Dogs?

A mast cell tumor (MCT-Mastocytoma) is a type of tumor made up of mast cells. Mast cells are a type of white blood cell that is found in various tissues throughout the body. Like any cell in the body, mast cells can develop cancer, resulting in a MCT. Mast cell tumors are most commonly found in the form of nodules on the skin, but can also affect other parts of the body.

What are mast cells?

Mast cells play a big role in allergic response, as they release chemicals once exposed to allergens in the body. One of the main chemicals released in this process is histamine, which is responsible for causing itchiness, sneezing, and runny eyes. When histamines and other compounds are released in excessive amounts, this can result in anaphylaxis (severe allergic reaction) and full body reaction. Mast cell tumors are made up of these “allergy cells’, and require special care when being investigated for this reason.

Mast Cells

What are the signs and symptoms of mast cell tumors in dogs?

Unfortunately, mast cell tumors do not have a characteristic form.  MCT’s can present in many shapes and sizes, and on any part of the body. They can appear large, small, hard, soft, or even ulcerated. For this reason, it’s important to examine your dog regularly, and have routine vet visits. While there are no set rules for MCT’s, there are a few signs and symptoms to keep in mind:

  • Lesion or growth on the body: Since a MCT can present in any form, it’s important to take any new growth or lesion seriously. Any growth could be a possible mast cell tumor.
  • A mass that fluctuates in size: Because MCT’s contain histamine and other allergic response compounds, this can result in swelling and irritation to the mass. This may present as a mass that appears to be changing in size, sometimes day by day.
  • Enlarged lymph nodes: Swelling and enlargement of lymph nodes can appear in areas near the tumor.
  • Gastrointestinal upset: As the cancer cells spread, they can start to affect other parts of the body. Once the gastrointestinal tract is affected, you may start to see vomiting, diarrhea, anorexia, and weight loss.
  • Signs of malignancy: Once the cancer has spread, a dog will begin to show symptoms of other areas affected. This could mean coughing, weight loss, elevated liver values, wounds that won’t heal, and other signs that other major body systems are being attacked.

Complications of mast cell tumors in dogs?

Since a mast cell tumor is a form of cancer, obvious complications stemming from any type of cancerous mass will be present. Because of a mast cell tumor’s unique make up of mast cells, there are some specific complications that can come along with this diagnosis. Degranulation is the process in which histamine and other allergen response compounds are released into the body by a mast cell. In this process, some of these compounds will be released into the bloodstream in excessive amounts. This can result in ulcers in the stomach or intestines, lethargy, vomiting, and a severe allergic response called anaphylaxis.

Degranulation can be triggered by pressure, so manipulating the tumor in any way can be risky. This is why we strongly advice pet owners to not allow their pets to lick or scratch any masses, and why anti-histamines are used prior to investigating masses in a clinic setting.

Mast Cell Tumor

How is a mast cell tumor diagnosed?

A mast cell tumor is often diagnosed by a fine needle aspirate (FNA). This involves taking a small needle with a syringe, and suctioning the cells directly from the tumor and putting them onto a slide to be examined. A biopsy is then performed for a definitive identification of the grade of the cells in the mass, and the stage the disease is in. Once a diagnosis has been made, a doctor will then recommend other diagnostic testing to check for the potential spread of the disease. These diagnostics will include blood work to check organ function, diagnostic x-rays to check for metastasis in the chest, and ultrasound imaging to explore further for manifestation in other areas. It’s essential to know the stage in which this condition has progressed in order to understand a prognosis. The stages of the disease include:

  • Stage 1: Characterized by a single tumor without metastasis.
  • Stage 2: Characterized by a single tumor with metastasis into the surrounding lymph nodes.
  • Stage 3: Characterized by multiple skin tumors, or by a large tumor that has invaded subcutaneously.
  • Stage 4: Characterized by the presence of a tumor, with metastasis to an organ or widespread mast cell presence in the blood.

What are the treatment options for a mast cell tumor?

Treatment for mast cell tumors will depend entirely on the progression of the disease in each patient. Options for treatment of mast cell tumors include:

  • Surgery: Surgical removal is the ideal treatment of MCT’s, as long as the cancer can be entirely removed and has not spread.
  • Chemotherapy: Chemotherapy is used to treat MCT’s that have already spread to other parts of the body, or have a high risk of spreading.
  • Radiation: Radiation can be used in place of surgery, or when cells may remain after surgery has already been performed. While radiation is beneficial, it also comes with risk of damaging healthy tissue along with the cancer invaded tissue.
  • Symptomatic treatment: While symptomatic care does not offer a treatment to the disease, relief can be found in offering medications for pain, nausea, GI upset, and other symptoms associated with the disease.

Life Expectancy, Survival and Prognosis

Prognosis for mast cell tumors will vary by case, but an early diagnosis is the common factor in a favorable outlook for a dog with a MCT. When tumors can be completely excised with surgery with no cancer cells left behind, a cure for this disease is highly possible. When a MCT has spread and affected other parts of the body is when the survival rate begins to decrease. In situations of metastasis, exploring each avenue of treatment will only improve the chances of a possible cure.

Once a dog has been cured of a MCT, frequent physical exams and skin checks by a veterinarian will help to prevent a future complication from re-occurrence.


Mast cell tumors are called the “great pretenders” for a reason. They are notorious for disguising themselves as harmless nodules, while they wait to wreak havoc on your pet’s health. Make sure to take any lesion on your pet seriously, and keep this dangerous invader in mind! Fast action can help to save your dog in the fight against mast cell tumors!

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Amber, a dedicated animal enthusiast, has seamlessly merged her passion for animals with her career as a Licensed Vet Tech and content creator. Her journey is a testament to her commitment to educating pet parents through informative articles. With a degree in Veterinary Technology, she has become a prolific writer and a professional dog trainer. Amber's expertise spans veterinary medicine, pets, and shelter medicine. Her Amazon published book, "Heal My Fractious Heart - A Vet Med Romcom," showcases her creative writing talents. Currently residing in Chiang Mai, Thailand, she manages marketing and social media for a preventive pet health subscription company called Vetted.


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