A normal mast cell is a part of the immune system that helps defend against invading organisms like parasites. They are found within systems that come in contact with the outside world such as skin, respiratory, or intestinal tract. Mast cells contain small granules of inflammatory biochemicals meant for use against invading parasites. The outside of the mast cell is lined with antibodies that grasp antigens that alert when a parasitic invasion is occurring. When this happens the mast cell releases these granules like a landmine. As the granules are released a toxic biochemical harms the parasite along with alerting other cells that a battle is in progress and that they need to come help. This is how a mast cell is supposed to work.
The problem occurs with the fact that the world today is much cleaner and much fewer parasites are trying to invade the system. Since they have less work to do mast cells find new antigens to become stimulated by other that parasites. One of the most common antigens these cells set their sites are pollen proteins. When the attacks on pollen proteins occur, there is no parasite to kill and instead the biochemicals produce redness, itchiness, and swelling. This is your classic allergic reaction.
A mast cell tumor is a mass that is made up of many mast cells. When this happens the cells can become unstable and release their toxic granules creating a random allergic symptoms in the area of the tumor. Mast cell tumors can be very invasive and difficult to treat.
Mast cell tumors are much more common in the following breeds. If any kind of lump or mass appears in dogs of these breeds it is very important to have it checked out by your veterinarian.
Boxer English Bulldog Boston Terrier Chinese Sharpei Labrador Retriever

Golden Retriever Miniature Schnauzer Cocker Spaniel
Mast cell tumors typically appear on the skin but they can come up anywhere that mast cells are present. They do not have a characteristic appearance and can look like any type of skin mass. The biggest indicator that a skin mass could be a mass cell is its ability to swell. Owners often notice that the site swells suddenly, turns red, or becomes itchy due to the release of the toxins. Diagnosis of a mast cell tumor can typically be made with a needle aspirate. This means that a small needle is inserted into the mass to draw off cell.
This sample is then viewed under a microscope after being stained. The granules of the mast cell have a very distinct appearance once stained. After a tumor has been diagnosed as a mast cell the next step is to take it off along with any other suspicious skin masses.
At this time the mass is sent off to a pathologist to have the mast cell graded.
The grade of a mast cell is an indication of the malignant characteristics of the cells under the microscope. The most common scaling system is known as the Patnaik system. A
Grade I tumor is considered benign, while a Grade III is considered malignant. Grade II tumors have the potential to go either way making them the most unpredictable.
If your pet is going to have a mast cell tumor a Grade I tumor is the best type to have.
These types of tumors generally do not spread beyond the place they are located with in the skin. This means that surgical removal is typically curative. With any mast cell tumors wide margins need to be taken around the mass to achieve complete removal. If the entire mass has not been removed Grade I tumors tend to grow back at a slow pace.
About 50% of mast cell tumors are a Grade I and can be cured with surgery alone.
A Grade II tumor is very unpredictable do to the wide range of malignancy that falls into this category. Radiation therapy is available through referral to a specialist and is considered curative for this type about 80% of the time. If surgical removal is the only available option close attention should be paid to any other masses that appear along with regular veterinary check ups to evaluate any possible spread to the patient’s lymph nodes.
Grade III is the worst type of mast cell tumors to have. They represent about 50% of all mast cell tumors and are very invasive and aggressive. Chemotherapy is an option for these tumors but the do tend to spread very rapidly.
With mast cell tumors it is important to evaluate the staging of the tumor. The staging of the mast cell tumor is based on the areas affected, how deep into the tissue the tumor is, and whether or not other body systems such as the lymph system are involved. To evaluate these things the following tests may be needed.

A basic blood panel helps to see how all of the other organ systems are functioning. It helps to see the health of the liver and kidneys, which can help your doctor decide which drugs may work best. It also helps to see if there are any mast cells circulating with in the blood stream or if anemia is present. A Buffy Coat Smear is another test that may be recommended. The buffy coat is a small layer of white blood cells that float atop the layer of red blood cells when a capillary tube of the patient’s blood has been spun down.
This layer of cells is then smeared onto a slide and checked for circulating mast cells. In some cases a bone marrow tap maybe need to properly get an idea of circulating mast cells.
Lymph node aspirations are very often performed to the lymph nodes closest to the location of the tumor. This procedure is performed in the same manner as the aspiration of the mass except that is a lymph node that the needle is inserted into. The purpose of the lymph node aspiration is to see if the tumor has spread to the lymph system.
In some cases other factors can affect the ability to properly treat a mast cell tumor. The first of which is location. Tumors that arise on the feet, genitals, muzzle, and oral cavity tend to be a little more malignant and can become intertwined in blood vessels and nerves in the area. This makes complete removal impossible for some of these cases. The amount of skin available in the area of the tumor can also make it difficult to remove the ideal amount of tissue surrounding the tumor. Another factor is the growth rate of the tumor. Masses that have been there for months or years tend to be a little less malignant than tumors that grow more quickly, however it is still important to get all tumors examined by a veterinarian.
Treatment for mast cells tumors consists of surgical removal of the mass along with any affected lymph nodes. For removal of the mass wide margins need to be taken around it to insure complete removal. This means that although the tumor could be very small the incision site maybe much larger than most people would expect. The pathologist will review the margins to make sure the tumor was completely excised when the tumor is sent off for grading.
Radiation and chemotherapy are also options for dogs with mast cell tumors that are more invasive or malignant however some of these treatments require a special facility to perform and can be quite expensive. If you are interesting in pursuing these treatments please contact your veterinarian for referral to a veterinary oncologist in your area.
Mast cell tumors are a common yet potentially dangerous occurrence in dogs. It is very important to get all growths examined by a veterinarian shortly after discovery.