MAST CELL TUMOR IN DOGS

Mast cell tumors are one of the most common skin tumors in dogs. They develop from mast cells, an element of the body’s immune system that normally causes allergic reactions and inflammatory responses. When they turn into cancerous forms, these abnormal mast cells create solid growths on or beneath the surface of the skin.

Mast cell tumors can be especially challenging due to their variable behavior. Some remain relatively small and do not exhibit rapid progression for many years, however, some exhibit aggressive behavior with metastasis to distant organs, including the spleen, liver and bone marrow. Due to this variability, each skin mass found on a dog should be evaluated promptly as opposed to being considered harmless.

Causes

The exact causes of mast cell tumors remain unclear. Multiple risk factors have been identified for mast cell tumor development.

Genetic Influence

Genetic influence has a high degree of importance. Several breeds exhibit a higher incidence of mast cell tumors, which suggests they have an inherited disposition to grow abnormally.

Commonly affected breeds include:

• Boxer
• Labrador Retriever
• Golden Retriever
• Bulldog
• Boston Terrier
• Pug

Cellular and Biological Factors

Studies demonstrate that mutations in specific genes associated with cellular proliferation (c-KIT) occur frequently in mast cell tumors. This results in uncontrolled division of mast cells.

Other Possible Factors

Although it is not well established, other potential contributors to mast cell tumor development include:

• Chronic dermatitis/inflammation
• Dysregulation of the immune response
• Some environmental influences (currently under investigation)
• Age: The majority of affected animals are typically classified as middle aged to geriatric

Symptoms

Beginning with mast cell tumors, “the great imitator,” due to their ability to mimic many benign skin problems, they are typically identified by the presence of a skin mass. The appearance of the tumor will have a wide variation depending upon whether it feels firm or soft, is raised from the surface, and where it occurs on your body. Other symptoms can occur, including

• A lump that changes size over time
• Redness or swelling around the mass
• Itching or irritation at the site
• Ulceration or bleeding in some cases
• Sudden enlargement after being stable for weeks or months

Some tumors will produce histamines and other substances that might affect a dog’s entire body, causing problems like stomach upset and vomiting in more serious cases.

Risks

The risk of Mast Cell Tumors depends upon the degree of the tumor and when they are discovered.

Local Tissue Damage

Even though the tumors are relatively small, they could still emit inflammatory substances:

• Swelling and redness
• Itching and discomfort
• Delayed wound healing after irritation or trauma

Internal Spread

In more aggressive tumors, they can be carried by the lymphatic system to other areas of the body, including:

• Lymph Nodes
• Spleen
• Liver
• Bone Marrow

Once the cancer has been distributed throughout the body, then treatment will become even harder and the prognosis worse.

Systemic Effects

Histamines produced from the tumor cells may result in Gastrointestinal symptoms like vomiting, reduced appetite, or stomach ulcers in rare cases.

Diagnosis

Mast Cell Tumors require an accurate diagnosis, as they closely resemble several benign growths. There are several types of diagnostic testing for Mast Cell Tumors, some are less invasive than others.

Fine Needle Aspiration (FNA)

This test is done by using a very fine needle that takes a sample of the lump’s cellular makeup. The sample is then evaluated microscopically. Many Mast Cell Tumors can be diagnosed via FNA.

Biopsy and Histopathology

When the FNA results are inconclusive or when the veterinarian wants confirmation and needs to evaluate the aggressiveness of the tumor, a biopsy will be needed.

A biopsy is essentially the examination of tissue to help determine what type of cancerous cells, if any, are present in the body.

This process allows veterinarians to also perform a grading on the tumor, which is critical because the grade determines the potential aggressiveness of the tumor.

Staging Tests

Once a Mast Cell Tumor has been confirmed, your veterinarian may recommend staging tests to determine if the Mast Cell Tumor has metastasized. Some examples of staging tests include:

• Complete Blood Counts (CBC).
• Ultrasound evaluations of abdominal organs.
• Sampling lymph nodes.
• X-ray or advanced imaging studies.

Treatment

Treatment will depend on tumor grade, size, location, and whether it has metastasized.

Surgical Removal

Surgical removal is typically the first-line treatment for most localized mast cell tumors. The object of this is to remove the tumor along with a border of normal tissues, along with a margin of normal tissue to reduce the risk of local recurrence. Many times, in early, small, lower grade tumors, they can be completely cured after surgical removal.

Medical Therapy

If your pet was unable to have the surgery completed or had the cancer spread, there would need to be other methods to treat the cancer:

• Chemotherapy to slow down the cancer’s growth
• Targeted therapy (such as Tyrosine Kinase Inhibitors (TKIs) to slow down the cancer’s growth
• Corticosteroids to shrink the tumor and reduce the swelling
• Anti-Histamines to counteract Histamine Release

Radiation Therapy

Radiation therapy may be recommended when complete surgical removal is not possible or when histopathology shows incomplete margins.

Supportive Care

Supportive treatment is very helpful and includes medication to help with vomiting, protect the stomach lining and provide relief from discomfort.

Prevention

There is no known way to prevent mast cell tumors, but early detection greatly improves treatment options and outcomes.

It is recommended that owners inspect their dog’s skin for new lumps or changes in old ones. If a lump appears, increases in size, or irritates, owners should take them to a veterinarian immediately.