Maybe it's just a tiny mass on Fido's chest, or a new bump on Fluffy's neck. It may look harmless, but mast cell tumors can look like anything. Even a lipoma, a benign fatty tumor many older dogs get, can easily be misdiagnosed without further testing.
Dr. Alison Book is an oncology resident at the University of Illinois Veterinary Teaching Hospital in Urbana. She says, "mast cell tumors can have a wide range of behavior and prognoses in the dog." They also have varying appearances and can mimic other tumors. Similar to lipomas, they may feel soft and moveable; alternatively they can be firm, red or inflamed lesions. In short, you can't judge a tumor by its cover.
It is for this reason that Dr. Book recommends that your veterinarian aspirate any bump found on your dog that looks suspicious. An aspirate is simple to perform and not very stressful to the patient either. A veterinarian gently sticks a small gauge needle into the mass and fenestrates (small movements) or aspirates (pulls back on the syringe) to pull out cells within the mass. With this aspirate, experts can review the cells under a microscope.
In the case of mast cell tumors, under microscopy you will see, like the name implies, increased numbers of mast cells. These cells normally inhabit certain tissues in the body and are associated with inflammation such as allergic reactions. Release of substances contained within mast cells, such as histamine, are responsible for the red and itchy tissue response. For example, the over-the-counter medication Benadryl is an antihistamine, which helps to counteract the histamine released from mast cells when a stimulus sets them off.
However, the growth of a mast cell tumor is not a normal, natural process in the body. "These tumors occur when the growth and development of a population of mast cells is no longer appropriately regulated by the body," says Dr. Book, "the mass occurs as the result of too many cells accumulating in one location, and in some cases, behaving badly."
The prognosis for a mast cell tumor can vary drastically depending on several factors but correlates most strongly with what the pathologist, a veterinarian specializing in diagnosing disease from body samples, finds. With a biopsy, a small part of the tumor is removed--something which is easily accomplished in many cases with a shot of local anesthetic to numb the area, and then a biopsy punch tool that quickly removes a small portion.
This tissue sample is then sent to an expert who will confirm the patient has a mast cell tumor and assign it a grade from 1-3. "Grade 1 mast cell tumors may be surgically cured with complete removal," notes Dr. Book. And hearing the word "cure" from an oncologist is something to get excited about, considering the worst grade, a 3, is not likely to be cured by the time it is diagnosed. With grade 3 tumors, it can be much more difficult to control both local disease and dissemination to other parts of the body. Treatment for grade 3 mast cell tumors is very dependent on each individual situation, but in some cases you are simply trying to provide a remission and/or palliative care and prolong the animal's life, as well as improve their quality of life.
In the end, what is important to remember is that a mass that looks benign really may not be. If you are lucky enough to catch the tumor sooner rather than later, there is a much better chance your veterinary oncologist will mention the word "cure" in their treatment plan, rather than the much dreaded words, "average survival time," in the prognosis.
If your four-legged friend has a bump, or you have questions regarding tumors in your pet, contact your local veterinarian.
An archive of Pet Columns from the University of Illinois College of Veterinary Medicine is available online at www.vetmed.illinois.edu/petcolumns/. Requests for reprints of this article may be directed to Mandy Barth, email@example.com.
Veterinary Extension/Office of Public Engagement
University of Illinois College of Veterinary Medicine