Should I have my dog’s mast tumor removed?

Q: When I took my dog in for a vaccine, the veterinarian found a small lump located on her lower shoulder area — near what I’d call the armpit. I first noticed this several months but didn’t realize that is was a tumor. I just checked to that it wasn’t a tick and let it go. I can’t really say if it has grown or not. It is now about the size of a blueberry and the exact color of her skin.

The doctor took a needle aspirate and told me it is a mast cell tumor. He is recommending removal of the tumor and the surrounding tissue for testing to see what “grade” of mast cell tumor we’re dealing with. I have been also considering having her teeth cleaned, but I would only want her to go under anesthesia once. Do you think it is worth having the mass removed and biopsied? Should I have a dental cleaning done, too?

A: I absolutely recommend removal of the cancerous tumor. Mast cell tumors can be fatal and could spread through the blood without ever appearing aggressive on the outside. Current guidelines recommend a surgical margin of 3cm and one fascial layer deep. That’s a pretty big cut for a bump that most people wouldn’t notice!

If the biopsy comes back as grade one, then most will be cured with surgery alone. Grade two masses with wide surgical margins also have a good prognosis, although they can return and still have the potential to have already spread. If the surgical margins are not clear by a wide margin, most oncologists recommend additional treatment for grade two tumors. Grade three tumors are likely to have already spread and warrant additional diagnostics and treatment.

Three quarters of mast cell tumors are either grade one or grade two. Unfortunately, there is no reliable way to grade the mass ahead of time. They generally look fairly harmless, but certainly can be real trouble. My priority would be to remove the tumor as soon as possible. 

In our practice, I generally recommend a dental procedure be scheduled as a second procedure on another day. Although I do occasionally make exceptions, I have three reasons for my ordinary preference.

First, there is a documented increased risk of surgical infection in dogs having a dental procedure on the same day. If done on the same day, your veterinarian can minimize the risk with the use of injectable antibiotics at the beginning of the dental procedure.

Second, a surgical plane of anesthesia is deeper than we need for dental procedures. I prefer a light plane for a short time when I’m cleaning teeth. I want to recover post-surgical patients quickly due to the depth of anesthesia they were under and it’s effects on blood pressure and body temperature.

Finally, on a more practical note, if the mass turns out to be aggressive you may want to use your financial resources to treat the cancer first. In the case that it has already spread and you do not elect chemotherapy, then clean teeth would not be a big priority. Without chemotherapy, a grade three mast cell tumor carries an unfortunate prognosis of only 4-5 months.

If the mass returns as a grade one or grade two with clear margins, then I would strongly recommend a second, lighter anesthetic episode if your veterinarian finds grade 2 periodontal disease or worse.

That level of gum inflammation is well documented to shorten a pet’s life span due to bacterial damage of kidneys, liver, heart, and blood vessels. In my opinion, the small, controlled risk of a short, light anesthetic procedure is far better than the uncontrolled, repeated daily risk of progressing periodontal disease.

Dr. Watts is a companion animal general practitioner and owner of Clevengers Corner Veterinary Care. He can be reached through ClevengersCorner.com or by calling 428-1000.