Mast cell tumors are the most common cancer found in dogs

A mast cell is a type of white blood cell. It is found in many tissues in the body. Mast cells are the allergy cells that are part of your allergic response. When it is exposed to allergens, it releases chemicals and compounds in a process called degranulation. One of these compounds is histamine which is most commonly known for triggering itchiness, sneezing, runny eyes or nose, which are some of the most common symptoms for things like hay fever or other allergies. However, if these compounds are released in larger amounts, it is called mass degranulation and can cause full-body effects such as anaphylaxis. MCT is a reactive disease, so degranulation is easily triggered by pressure, so you should avoid touching the tumor and your dog shouldn’t chew, lick or scratch is as well.

A mass cell tumor (MCT) is a tumor made from mast cells and commonly form nodules or masses in skin, but affect other areas of the body such as the spleen, liver, intestine and bone marrow. 60-70% of dogs with MCT develop one tumor.

MCT is more common in breeds such as Boxers, Bull Terriers, Boston Terriers and Labrador Retrievers.

Several genetic mutations are known to take part in the development of MCT. One of the more well known genetic mutations is to a protein called KIT that is part of the replication and division of cells.

MCTs on skin can occur anywhere on the body and don’t have a specific appearance. These bumps range from being raised lumps or bumps on or just under skin; red, ulcerated or swollen. They can also be present for months without growing or they can appear suddenly and grow rapidly. They can grow quickly after months of no growth or fluctuate, being bigger or smaller even on a daily basis.

When mass cell degranulation occurs, some of the chemicals and compounds created can go into the bloodstream and cause problems in other areas of the body such as ulcers in the stomach or intestines. This may cause more common side effects like vomiting, loss of appetite, lethargy and melena (black, tar-like stools that are related to bleeding). A less common symptom can be anaphylaxis. Very uncommonly, MCT in the skin can spread to the internal organs, causing enlarged lymph nodes, spleen and liver or peritoneal effusion (fluid build up) in the abdomen which makes the stomach look rounded or swollen.

The behaviour of the tumor depends on many factors. The tumor is graded from I-III, with grade I being less aggressive than grade III. The higher the grade, the higher the tendency for the tumor to spread to other parts of the body (metastasize).

The chances of recovering from this disease is lower if:

• MCT is a more common disease in the breed of the dog.
• The tumor is where the skin meets mucus membranes (for example, the gums)
• when seen under a microscope, the number of cells actively replicating is high

Despite the range in behaviour and appearance of MCT, it is one of the most treatable cancers, especially for lower grade tumors. If your dog is diagnosed with MCT, it is better to look at whether the cancer has spread to different parts of the body. For lower grade tumors that have no evidence of spreading, surgery would be the best option of treatment since chemotherapy wouldn’t be required and it is better long term. If the tumor is higher grade but has no evidence of spreading, combined surgery and chemotherapy is recommended. However, if the tumor isn’t in an optimal location for surgery or the surgery couldn’t remove all of the tumor, radiation therapy is a good alternative. It’s better to discuss the different treatment methods with your veterinarian and veterinary oncologist.

Resources:

https://vcahospitals.com/know-your-pet/mast-cell-tumors-in-dogs