What Is Mast Cell Tumor In Dog: Symptoms, Diagnosis, and Treatment

What is a Mast Cell Tumor in Dogs?

A mast cell tumor (MCT), also known as mastocytoma, is a specific type of skin cancer that stems from mast cells. Mast cells are white blood cells that can be found in several tissues and play a major role in allergic reactions. 

As a skin cancer, the mast cell tumor dog causes lumps and bumps that can imitate literally any skin lesion. Therefore, in a 2017 Frontiers study, “Are Mast Cells MASTers in Cancer?”, mast cell tumors in dogs are metaphorically compared to masters. 

Mast cell tumors are aggressive and tend to invade surrounding tissues. Also, although most common on the skin, the mast cell dog tumor can grow in other locations like the liver, bone marrow, and intestine. 

If the dog’s body is entirely affected by mast cell tumors, the condition is known as mast cell disease or canine mastocytosis. 

Are All Mast Cell Tumors in Dogs Cancerous?

No. Not all mast cell tumors in dogs are cancerous. 

Some MCTs are malignant (cancerous), while others could be benign (not cancerous). However, it is impossible to tell whether a tumor is cancerous or not without proper analysis. 

Therefore, as pet owners, you need to seek immediate veterinary attention if you suspect your dog has a mast cell tumor. 

What Causes Mast Cell Tumors in Dogs?

Mast cell tumors are caused by a combination of environmental and genetic factors in dogs. Therefore, it is hard to pinpoint the exact cause for the growth of canine cutaneous mast cell tumors. 

However, it is established that mast cell tumors are more likely to occur in certain dog breeds such as: 

• Boxers
• Pugs
• Labrador Retrievers
• Golden Retrievers
• Bulldogs
• Beagles 
• Bull Mastiffs 
• Boston Terriers
• Rhodesian Ridgebacks
• Labrador Retrievers 
• Golden Retrievers 
• Rhodesian Ridgebacks. 

What are the Symptoms of Mast Cell Tumors in Dogs?

Mast cell disease or mast cell tumors trigger an array of symptoms. The symptoms are non-specific and cannot be immediately linked with MCTs. Here is a list of the symptoms of mast cell tumor in dogs: 

• Skin lesions 
• Loss of appetite
• Vomiting
• Enlarged lymph nodes 
• Sluggishness
• Quick breathing
• Dog diarrhea
• Abdominal pain
• Weight loss
• Pale gums
• Acute lethargy
• Tarry stool

If your dog is showing one or more of these symptoms, consult your veterinarian. Considering the aggressive biological behavior of mast cell tumors, being proactive is vital.  

When do Symptoms of Mast Cell Tumors Usually Occur in Dogs?

Symptoms of mast cell tumors usually occur in dogs under one year. “Mast cell tumors in dogs less than 12 months old usually occur at a median age of 7.6 months at first presentation and 9 months at diagnosis,” according to the study by Rigas, K., Biasoli, D., Polton, G., Finotello, R., Murphy, S., Palma, S., Starkey, M., & Verganti, S. titled “Mast cell tumours in dogs less than 12 months of age: a multi-institutional retrospective study,” 2020.

Symptoms appear several weeks to months after the tumor develops. Factors such as the grade of the tumor (low, intermediate, or high), as well as its size and location, determine how quickly clinical signs manifest.

What are the Risk Factors for Mast Cell Tumors in Dogs?

The risk factors for mast cell tumors in dogs are listed below. 

• Breed Predisposition: Certain breeds have a higher genetic predisposition to developing MCTs due to inherited genetic factors.
• Age: MCTs are commonly diagnosed in older dogs between the ages of 8 and 10 but occur at any age.
• Specific Gene Mutations: Mutations in certain genes, such as c-KIT, are associated with the development of MCTs. The mutations lead to uncontrolled mast cell proliferation.
• Chronic Inflammatory Conditions: Dogs with chronic inflammatory conditions or frequent allergic reactions are at a higher risk of developing MCTs. Chronic inflammation stimulates mast cell proliferation and tumor formation.
• Exposure to Carcinogens: Environmental toxins and carcinogens, such as pesticides, herbicides, and industrial chemicals, increase the risk of developing MCTs. Long-term exposure to the substances leads to genetic mutations and cancer.
• Hormonal Imbalances: Hormones like estrogen impact mast cell behavior and proliferation, but the exact mechanisms are not fully understood.
• Immune System Abnormalities: An improperly functioning immune system fails to regulate mast cell activity, leading to tumor growth.
• Previous Tumors: Dogs that previously had mast cell tumors are at a higher risk of additional tumors due to genetic predispositions or remaining abnormal mast cells.

How is a Mast Cell Tumor in a Dog Diagnosed?

The mast cell tumor dog diagnosis starts with fine-needle aspiration (FNA). FNA is a procedure completed by the veterinarian using a small needle and a syringe to take a sample from the tumor. Then the sample is analyzed under a microscope. 

Instead of aspirating a sample, the veterinarian may use a piece of the skin tumor to collect a biopsy sample. This will help grade the system. For clinical staging of the mast cell tumor, the veterinarian may l order additional tests like chest radiographs and abdominal ultrasound. 

The malignancy of the mast cell tumor can be evaluated through the c-Kit status. Namely, c-Kit is a receptor found on the mast cells’ surfaces. Since c-Kit receptor mutations are linked with malignant changes, the presence of mutation can provide confirmation that the MCT is malignant.  

What are the Treatments for Mast Cell Tumors in Dogs?

There are several treatments for mast cell tumors which can be used alone or in conjunction with each other. Below is a more detailed explanation of the possible treatment options. 

Surgical Removal. Surgical removal is an ideal treatment option for dogs with low grade mast cell tumors that have not spread. However, if the MCT  has metastasized, surgery alone is sufficient. Surgery should also be carefully considered in older dogs with co-existing conditions and high anesthesia risk. 

Radiation Therapy. Radiation combined with surgery is the ideal treatment combination for managing mast cell tumors located in places where wide surgical excision is not an option. The drawbacks of radiation include its cost and the need for repeated sedation during the treatments.

Chemotherapy. Chemotherapy is based on the use of medications that can destroy cancer cells. It is recommended for dogs with multiple MCTs, high-grade MCTs, and MCTs spread to regional lymph nodes. Commonly used chemotherapy drugs for mast cell tumor treatment are Vinblastine, Lomustine, and Leukeran. Palladia (toceranib) is also popular and can be used at home as it comes in an oral form. 

Intratumoral Injections. A recent discovery in the treatment of mast cell tumors in dogs is Stelfonta. Stelfonta (tigilanol tiglate) is injected directly into the tumor and, based on the manufacturer, removes as much as 75% of the tumor after a single treatment. Stelfonta is applicable to dogs with non-metastatic mast cell tumors. 

Oral . Prednisone is a frequently used medication as it is low-cost and relatively safe. Prednisone protects the body from histamine, heparin, and enzymatic granules released during the degranulation of mast cells. Prednisone may help shrink the MCT, thus making surgical removal more straightforward.  

Antihistamines. Some dogs with MCTs benefit from antihistamines. In mast cell tumor dogs, there are high levels of free histamine (just like in dogs experiencing allergic reactions). High histamine levels affect blood pressure heart rate and cause ulcers. Antihistamine examples are H1 blockers (diphenhydramine or Benadryl) and H2 blockers (famotidine or Pepcid).  

Holistic Management. The latest holistic cancer treatment option is CBD (cannabidiol) oil. CBD is a natural remedy that boosts the dog’s health and may help with mast cell tumors. Plus, it is safe and rarely causes any side effects (minor gastrointestinal upsets are possible). We strongly recommend the Honest Paws Well Collection, which includes various premium-quality and human-grade CBD products. 

Should You Remove Mast Cell Tumors in Dogs?

Yes, removal of the mast cell tumors is the treatment of choice. As lesions, mast cell tumors are more invasive than they seem and require aggressive surgical removal.

By aggressive, we mean surgical removal of the tumor with wide safety margins. In cases of metastatic changes in local lymph nodes, they need to be surgically removed. The removal of the affected regional lymph nodes improves the treatment success. 

After the mast cell tumor is removed, it is sent for further examination (in terms of cytology and histopathology) to evaluate whether it was removed completely. 

If the surgical margins of the removed mast cell tumor are not wide enough, the veterinary oncologist will recommend a second surgery or maybe even an additional treatment, like radiation. 

What are the Complications of Mast Cell Tumors in Dogs?

The complications of mast cell tumors in dogs that can arise during or after treatment are listed below. 

• Ulceration and Infection: MCTs ulcerate and lead to open sores susceptible to secondary bacterial infections. 
• Swelling and Edema: The release of histamines and other chemicals from mast cells causes localized swelling and fluid accumulation (edema) around the tumor site, leading to pain and discomfort.
• Anaphylactic Reactions: The release of histamine and other inflammatory mediators from the tumor causes severe allergic reactions, including anaphylaxis. 
• Gastrointestinal Issues: Histamine release stimulates gastric acid secretion, causing gastrointestinal problems such as ulcers, vomiting, diarrhea, and appetite loss. 
• Spread to Lymph Nodes: MCTs metastasize to regional lymph nodes, enlarging them and spreading the disease.
• Distant Metastasis: Advanced MCTs spread to distant organs, including the liver, spleen, bone marrow, and lungs, complicating treatment.
• Blood Clotting Disorders: The release of chemicals by mast cells affects blood clotting, leading to disorders such as disseminated intravascular coagulation (DIC), which causes abnormal bleeding or clotting issues.
• Recurrence: There is a risk of recurrence at the original site or the development of new MCTs elsewhere in the body. Dogs with one MCT are at increased risk of developing additional tumors.
• Chronic Pain and Discomfort: The presence of MCTs, if they are ulcerated or infected, causes chronic pain and discomfort.
• Reduced Mobility: Tumors located on the limbs or in areas that interfere with movement reduce a dog’s mobility and activity levels, impacting their overall well-being.

What is the Life Expectancy of a Dog with a Mast Cell Tumor?

With surgery, the life expectancy for mast cell tumor dogs is six months. If the surgery is followed by chemotherapy, the life median survival time increases to 12 months. 

The exact survival expectancy depends on the mast cell tumor’s grade (grade I, grade II, or grade III). For example, mast cell tumors grade II and grade III are considered high-grade tumors and do not have a favorable prognosis (survival time of 4 to 6 months). 

The survival time also depends on the type of treatment. Namely, if the surgical incision of the mast cell tumor was incomplete, a second surgery and radiation therapy are advisable.

Is Mast Cell Tumor in Dogs Fatal?

Yes, a mast cell tumor in dogs can be fatal. However, that is not always the case. 

According to a clinical trial “Assessment of Canine Mast Cell Tumor Mortality Risk-Based on Clinical, Histologic, Immunohistochemical, and Molecular Features,” high-grade tumors (per the Kiupel grading system) have a fatality rate of 61%. 

In the same trial, low-grade tumors (which account for almost 90% of all MCT cases) have a low fatality rate of about 16%. Therefore the grade is an important prognostic factor. 

Luckily, with the advances in veterinary medicine, more specifically oncology, an MCT does not have to be fatal. However, it needs to be caught early and the treatment plan successful.