A Mast Cell Tumor in dogs is a neoplasm, and it is the most commonly occurring malignant skin tumor in canines. When a dog has a Mast Cell Tumor, it often affects more than just the skin. Metastases in the lymph nodes, spleen, or liver can occur. Additionally, the increased release of histamine by the degenerated mast cells can elevate stomach acid production, leading to gastric ulcers.

Occurrence of Mast Cell Tumors in Dogs: Which Breeds are Affected?

Both male and female dogs can develop Mast Cell Tumors. These malignant skin tumors are frequently diagnosed in older dogs aged eight years and above, but younger animals can also be affected.

Certain breeds are more prone to malignant skin tumors, including:

The causes and risk factors for the development of Mast Cell Tumors are not yet fully understood. Genetic abnormalities likely play a role, combining with environmental factors to lead to neoplastic transformation of mast cells. About 30 percent of dogs with Mast Cell Tumors have been found to have a mutation in the c-kit gene.

Recognizing a Mast Cell Tumor in Dogs

Mast Cell Tumors often manifest as enlargements in the skin or subcutaneous tissue. These may feel doughy or present as solid nodules. However, Mast Cell Tumors can also hide behind inflammatory skin changes such as redness or ulcerative lesions. Common locations for Mast Cell Tumors in dogs include paws, trunk, or the head.

Mast cells contain numerous granules with bioactive substances like histamine and heparin. When these granules are released, these substances enter the tissue and bloodstream, leading to local inflammatory reactions and systemic symptoms. Therefore, dogs with Mast Cell Tumors may exhibit additional abnormalities alongside skin changes, such as:

What Does a Mast Cell Tumor Look Like in Dogs?

Mast Cell Tumors do not have a characteristic appearance. They can occur at various locations on a dog’s body. Essentially, any skin change could potentially be a Mast Cell Tumor. Mast Cell Tumors can also hide inside lipomas. A diagnosis with the naked eye is not possible; the involved cells must be examined under the microscope.

How Fast Does a Mast Cell Tumor Grow in Dogs?

The speed at which a mast cell tumor enlarges or spreads within a dog’s body depends on the tumor grade and the dog’s immune status. “Low-grade” tumors exhibit a low tendency to spread, while “high-grade” tumors grow more aggressively.

Some mast cell tumors may grow larger and then shrink again: The substances released by mast cells can lead to tissue inflammation with swelling, which may gradually subside over time.

Diagnosing and Treating Mast Cell Tumors in Dogs

The earlier skin tumors are detected, the higher the chance of complete removal. As mast cell tumors in dogs are malignant tumors that can affect other organ systems besides the skin, further examinations are necessary depending on the determined tumor grade.

Diagnosis of Mast Cell Tumors in the Veterinary Clinic

The veterinarian diagnoses a mast cell tumor through fine needle aspiration and cytological examination. The microscopic image shows mast cells as round cells with violet-stained granules and numerous eosinophilic cells.

The determination of the tumor grade plays a role in the therapy decision and prognosis. Mast cell tumors are classified into grades I-III or “low-grade” or “high-grade” based on their tissue structure:

Simply looking at the cells under the microscope is not sufficient for grading. A tissue section of the tumor is required, and the mast cell tumor is sent to a laboratory after surgical removal. Before surgery, histological examination is also possible through a biopsy of the tumor tissue.

Around 70-80 percent of mast cell tumors in dogs are classified as grade I or grade II tumors. “High-grade” mast cell tumors are more aggressive and have a higher metastasis rate but occur less frequently.

When there is suspicion of a tumor, the veterinarian will conduct a blood test to assess the general health of the dog. Sampling from surrounding lymph nodes, chest X-rays, and an abdominal ultrasound provide information on whether metastases have formed.

Treatment Options for Mast Cell Tumors

If the dog’s skin lump is a mast cell tumor, surgical removal is the treatment of choice. In some cases, complete resection is not possible due to the location, and local therapies or medications are used. Chemotherapy or radiation is also employed when the tumor has already formed metastases or when reducing the tumor size before surgery is necessary.

One medication prescribed for mast cell tumors is Masivet. The active ingredient Masitinib is a tyrosine kinase inhibitor that selectively inhibits the mutated receptor protein, thereby suppressing tumor growth. The medication is used for non-resectable grade II or grade III mast cell tumors. However, the mutation of the c-Kit tyrosine kinase must be proven before using Masitinib.

Survival Time for Dogs with Mast Cell Tumors

If a “low-grade” mast cell tumor is detected early and completely removed, it can mean a cure for the dog. These animals typically have a normal life expectancy. In cases of incomplete removal but additional radiation therapy, the prognosis is also favorable. Conversely, “high-grade” tumors have an unfavorable prognosis, with a median survival time ranging between six and twelve months.

Up to 17 percent of animals with a mast cell tumor develop additional mast cell tumors. Regular examination for new skin changes is, therefore, the most important preventive measure.

Importance of Nutrition

Tumor cells primarily utilize carbohydrates as an energy source. Additionally, they deprive the body of essential nutrients and energy, causing the dog to lose weight and suffer from emaciation. A “cancer diet” should contain fewer carbohydrates but a higher proportion of protein and fat to compensate for energy loss. Supplementing with vitamins and minerals helps strengthen the dog’s immune defense.