Veterinary perspective: MCTs (mast cell tumours)

Dr. Joanna Bronson

Sometimes that little bump or bump starts to feel different. It may be nothing or it may turn out to be a more serious threat to your pet’s health. Now is the time to make an appointment with your veterinarian.

However, before making that date, ask yourself these questions:

  • Did the lump or bump appear suddenly?
  • If it has been around for a while, has it changed significantly?
  • Is it harder, has the color, shape or size changed?
  • Is your pet acting normally or has his behavior changed?
  • Is he reluctant for you to touch the spot?
  • Have you and your pet been in a place where it could have been bitten by an insect or has it ever had an allergic reaction, such as hives?

These are the questions your vet will ask you to get a history of the humpback.

Mast cell tumors are a common form of skin cancer in pets.

Mast cells are a type of white blood cells found in many body tissues. These are allergic cells that play a role in the allergic response to an allergen. Their job is to release chemicals and compounds (including histamine) that cause itching, sneezing, and runny nose and eyes. This defense process is called degranulation.

The problem with mast cells going rogue occurs when excessive amounts (called mass degranulation) are released. This mass exodus can cause anaphylaxis, a severe, life-threatening allergic reaction.

A mast cell tumor is made up of mast cells. These form as nodules or lumps in the skin and can also form inside the spleen, liver, intestine and bone marrow. The most common tumors are skin tumors and most affected dogs have a singular tumor.

Since mast cells are always present in the body, the cause of their transformation is usually not a singular factor. Most seem to be caused by a mix of risk factors, some of which are environmental and some of which are genetic or hereditary.

We know that certain breeds seem to have a greater risk of developing these tumours. Some of these breeds include Boxers, Bull Terriers, Boston Terriers, and Labrador Retrievers.

The difficulty in noticing these tumors is that they vary in appearance and can appear anywhere on the body. They can be described as a raised lump or bump on or just under the skin. They may be red, ulcerated or swollen. Some may stay the same for months, and some may appear suddenly and grow very quickly. They may also change in size daily as the surrounding skin reacts to the agitation of degranulation.

Mast cell degranulation can release chemicals and compounds into the bloodstream and affect internal organs. Ulcers can form in the stomach or intestines and cause vomiting, loss of appetite, lethargy, and melena (black, tarry stools indicating internal bleeding). Some cases cause enlarged lymph nodes and complications of the spleen and liver which can cause fluid to build up in the abdomen, giving the belly a rounded and swollen appearance.

This is very scary information and the only way to know for sure if your pet has a MCT (Mass Cell Tumor) is usually a fine needle aspiration where a needle is inserted directly into the tumor and a sample of cells is aspirated and examined. under a microscope. In aggressive cases, a surgical tissue sample (a biopsy) can provide a more definitive diagnosis.

The pathology report can access the aggressiveness of the cancer and determine if it has or could spread to other parts of the body.

The prognosis is less favorable if the dog is of one of the susceptible breeds, the MCT is located where the mucous membranes are next to the skin (such as in the gums), and when examined under a microscope, the number of replicating cells is high.

The good news is that MCTs are one of the most treatable types of cancer, if labeled as low-grade. Surgery is the best option if there is no evidence of spread. In high-grade cases, even without signs of spread, surgery plus chemotherapy is recommended. Radiation therapy is another treatment option.

Not all MCTs are treatable, other factors to consider are the location of the tumors, the age of the dog and the cost of treatment.

An early review can help determine the best course of action for any treatment plan.

Dr Joanna Bronson of Bronson Veterinary Services, located at 452 W. Central Road, Coldwater. Contact her at 517-369-2161 or visit

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