Mast Cell Tumor In Dogs – Diagnosis, Treatment, & Prognosis

Mast cell tumors (MCTs) are the most common malignant skin cancer in dogs and account for approximately 16-21% percent of all skin tumors in dogs.

Normal mast cells that are present in connective tissues throughout the body are part of a dog’s immunologic defense systems against parasites and allergies. They can be activated to release a wide variety of inflammatory mediators (e.g. allergens, pathogens) and are key players in the inflammatory response.

A mast cell tumor (Mastocytomas) is the most common form of masses or nodules in the skin; they have a wide range of appearance, from very deep and fixed to raised and superficial; they may feel firm or soft and saggy. Most dogs (50-60%) with MCT only develop one tumor.

MCTs from anywhere in the dog’s body but typically lie within the dermis and/or subcutaneous layer. The majority of mast cell tumors (50%) are formed in the trunk and perineum; followed by extremities - such as the paws (40%) and the head and neck region (10%).

• New skin lesion/ raised bump or lump or just under the skin
• Enlarged lymph nodes / spleen/liver (rarely)
• Fluctuation in size
• Unexplained allergic reaction
• Redness and edema (skin and subcutaneous tumors)
• Sudden growth after long periods of inactivity or slow growth
• Inflammation / Itchiness of the mass (due to higher levels of histamine in the tumor)
• Loss of appetite
• Melena (black, tarry stools)
• Vomiting, and/or diarrhea

Survival rate and prognosis are dependent on the grade and stage of the tumor, and how promptly treatment is given.

Grade I mast cell tumors:

• Surgical removal is the option.
• Chemotherapy is generally not required.
• When complete surgical excision is not possible, radiation therapy alone or a combination of radiation and marginal surgical removal are the next best options.

Grade II mast cell tumors:

• Wide surgical excision.
• When wide surgical excision is not a viable option, a combination of marginal surgery and radiation therapy or chemotherapy.
• Metastatic/ multi-centric disease- Chemotherapy is generally utilized.

Grade III mast cell tumors:

• Chemotherapy is recommended due to this tumor's high metastatic potential.
• Several drugs are used to maximize the effect.
• Supportive measures such as antihistamines and antacids are recommended.

The MCT is irreversible without medical management and doesn’t cure on its own that is why vets emphasize surgical intervention.

Prevention is not possible for MCTs. Treatment and survival rates vary depending on the grade and stage of the tumor.

Good overall health and early detection are the only ways to prevent MCTs.

Check your dog on a regular basis and consult your veterinarian immediately if you find any odd lumps or lesions.

Boxer, Bull Terrier, Boston Terrier, Golden Retriever, Labrador Retriever, Schnauzer, Bulldog, American Pitbull Terrier, Pug, Rhodesian Ridgeback, Staffordshire Bull Terrier, Weimaraner

Causes:

The cause of the development of this tumor is not easy to understand. Very few tumors have a single known cause.

It is thought that there are several genetic mutations are involved in MCT development. One recognized mutation is to KIT protein (CD117), a transmembrane, tyrosine kinase growth factor receptor that is involved in the division and replication of cells.

Grading:

• Grade 1: Well-differentiated cells. Recurrence rate- 25%. Metastasis- Low chance.
• Grade 2: Intermediately differentiated. Recurrence rate- 45%. Metastasis- Potential to be locally invasive.
• Grade 3: Poorly differentiated. Recurrence rate- 75%. Metastasis - High potential.

Kiupel 2-tier grading has become popular recently.

Low-grade: Absence or low numbers of mitotic figures and fewer nuclear changes.

High-grade: Frequent abnormalities in the nucleus of the mast cells and/or mitotic index of 7 or higher.

Morbidity:

Stages of MCT:

• Stage 0: One incomplete tumor with no involvement of lymph nodes.
• Stage I: One tumor without metastasis + no lymph node involvement.
• Stage II: Single tumor + metastasis + lymph nodes involvement causing secondary growth.
• Stage III: Multiple or large or infiltrating skin tumors + may or may not have lymph node involvement.
• Stage IV: Presence of one or more tumors + metastasis +distant Lymph nodes will be involved.

Substage A - No signs.

Substage B - Signs such as diarrhea and vomiting.

Diagnosis:

• Complete blood profile and urinalysis
• Abdominal ultrasound
• Fine needle aspirates
• Chest radiographs
• CT scan
• Tissue biopsy

Mortality:

Tumor-Related Mortality:

Grade 1 - 0%

Grade 2 - 25%

Grade 3 - 65%

Prognosis:

This tumor's activity is complicated and depends on many factors. In general, the tumor is graded from I-III; with the grade, I being less destructive than grade III MCTs. Tumors have a higher tendency to metastasize when moving from I-III.

Typically, the prognosis is less favorable if:

• The dog is the susceptible breed category.
• The number of cells actively replicating is high (when viewed under the microscope).
• The MCT is sited at crossroads where the mucous membranes meet the skin (e.g., the gums).

Grade I MCTs can have a good prognosis: surgery and conventional radiation therapy.

Grade II MCTs can still have a good prognosis after treatment including surgery, radiation, and chemotherapy. Expected Survival times are over 5 years.

Grade III MCTs that have metastasized to several sites have a guarded prognosis. The expected survival time is only months, even with surgery and chemotherapy.

Contact your vet right away, if you notice any of the following:

• Mysterious lumps or nodules.
• A known lump or bump that has changed in size or color.
• An inexplicable allergic reaction or hive.

Nutritional management for MCT: Diet high in protein, high fat, and low in carbohydrates.

35% animal protein + 35% fat (animal sources) + 20% carbs + remaining omega 3s + DHA + arginine + antioxidants + other minerals.

• Protein - Chicken breasts, turkey breasts, liver, ½ Cup Raw Salmon (cooked if you prefer).
• Omega3s - Salmon, tuna, and herring.
• Antioxidants - Blueberries, blackberries, Steamed broccoli, spinach, cooked yellow squash, kale, and green beans.
• Fats - Chicken/turkey fat or beef tallow.
• DHA - Mackerel, salmon, herring, sardines, and caviar.

As with any cancer, proper and earlier diagnosis, as well as aggressive treatments, gives more successful outcomes.

The solitary grade I and grade II MCTs prognosis that is completely removed is very good. The survival rate is 3-5 years.

For incompletely removed grade I and II tumors prognosis is poor but when they are treated with definitive radiation therapy, it turns out good. There is very less chance of local tumor recurrence within 3 years of radiation therapy.

Grade III mast cell tumors prognosis is guarded to poor.