Mast Cell Tumors In Dogs

What are mast cells?

Mast cells are immune system cells usually found in the skin, gastrointestinal tract and respiratory tract.

They release bioactive substances such as histamine, heparin, prostaglandins and proteolytic enzymes as part of the body’s defense mechanism. The chemicals cause symptoms of allergic reaction: itchiness, swelling, inflammation and increased gastric acid production.

Mast Cell Tumors in Dogs

Mast cell tumors in dogs usually develop on the skin, thereby accounting for about 20% of canine skin tumors. They can also occur in the intestines, spleen, liver or wherever mast cells exist.

Mast cell tumors are more prevalent in certain breeds of dogs. They include boxer, English Bulldog, Boston Terrier, Shar Pei, Labrador Retriever, Golden Retriever, Pug, Schnauzer and Cocker spaniel. Mast cell tumors tend to affect older than younger dogs.

Mast Cell Tumors in Dogs Symptoms

Mast cell tumors of the skin can occur on the trunk, limbs and head. They can appear as single or multiple raised lumps or lesions.

Other symptoms arise from unregulated release of bioactive substances as a result of tumors that develop in mast cells. They include gastrointestinal ulcer, blood clotting problems, vomiting blood, loss of appetite, blood in stool, bruising, lethargy, diarrhea and pain in the abdomen.

When the lump is touched or pressed, it may become irritated, swollen and itchy due to histamine released by mast cells.

Diagnosis of Mast Cell Tumors in Dogs

A fine needle aspiration determines the existence of mast cell tumor. This involves collecting tumor cells with a needle and examining them under a microscope.

Mast Cell Tumor Grades and Stages

Grading and staging are carried out during a biopsy of surgically removed mast cell tumor. The grade and stage of tumor are important for ascertaining the need for further treatment and prognosis.

Grading indicates the malignant characteristics of tumor.

Grade 1: localised and tend not to spread
Grade 2: fairly malignant
Grade 3: highly invasive and aggressive

Staging measures the extent of tumor spread. The stages range from 0 (1 tumor in the skin, no metastasis) to 4 (single or multiple tumors in the skin that have spread, lymph node involvement)

Treatment of Mast Cell Tumors in Dogs

The main treatment for mast cell tumor in dogs is surgery. In addition to the tumor, a large margin of healthy tissues surrounding the tumor must be removed to ensure no cancerous cells are left behind. Most grade 1 and 2 tumors can be treated with surgery effectively.

If the tumor is not completely excised, another surgery is recommended to remove remaining cancerous mast cells and additional healthy tissues.

Radiation is used if a second surgery is not possible due to insufficient margin of healthy tissues around the tumor or for recurrent tumors.

Radiation therapy is most helpful when mast cell tumors have not metastasised.

Chemotherapy may be used for treating mast cell tumors (grade 2 and 3) that have spread, are inoperable or recurrent tumors.

Mast Cell Tumors in Dogs Prognosis

Prognosis is determined by tumor:

– grade and stage
– location
– growth rate

Grade 1, stage 1 tumor has the best prognosis.

Poor prognosis:
– higher grade and stage tumor
– tumor on muzzle, mouth, genital region, nail bed, bone marrow, internal organs
– tumor with recent, rapid growth rate is likely to be malignant
– recurring tumor after removal by surgery

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