Mast cell tumors are the most common skin tumors on dogs, accounting for close to 20% of all skin tumors. Some dogs are more prone to developing them, such as boxers, pugs, bulldogs, and golden retrievers, but they can occur on any dog. The average age of the dog is 8-9 years.
Mast cell tumors vary in appearance–we can’t diagnose them just by looking at them. Often they are hairless, raised, pink growths on the skin, but they can be found under the skin, too. They can be very small or quite large and extensive. The only way to diagnose them is to do a fine-needle aspirate – sticking a needle into the tumor and getting cells out to examine under the microscope. Mast cells are very distinctive looking, so the diagnosis is usually straight-forward.
When we diagnose a mast cell tumor, we recommend surgically removing it. But it is important to get wide margins around and under the tumor, making it less likely to recur. This is pretty easy to do if the growth is on the dog’s body (about 50% of the tumors), but if it is on the face, paw, legs, tail or other areas with not much skin, surgical removal is much more difficult.
There is a new treatment available for these tumors called STELFONTA. This drug is injected into the mast cell tumor and causes lysis and death of the tumor cells, leaving healthy tissue. Within hours of injection, there is inflammation and swelling of the tumor. Within a week, the tumor has died and sloughs off, leaving a wound with healthy tissue underneath. Depending on the size of the tumor, there can be a big hole where the tumor was, but after about a month, the wound has healed and the fur is starting to regrow. Most dogs only require one injection, but some do need a second one.
The benefit to treating a mast cell tumor with Stelfonta is that your dog won’t require anesthesia (possibly sedation, but often not) and there is no concern with stitches or an e-collar (in fact, it is actually good if the dog licks the dead and dying tissue from the wound!). Dogs receiving Stelfonta do take prednisone (a steroid) for 10 days, as well as an anti-histamine and stomach protectant for the first 7 days (when the tumor is dying).
If you have more questions, feel free to email us!
Dr. Scarlett
