A diagnosis that no veterinarian is happy to make. As soon as the word is spoken, it shatters space. It was no different this time. “It’s cancer. Max has a malignant mast cell tumor. I am so sorry.”
The mother of two, sitting across from me, immediately began to sob. The handsome Labrador Retriever at her feet looked up in concern. When I offered her handkerchiefs, I thought about how we got here and where we were going. Neither of us knew that a miracle was waiting.
What is a mast cell tumor?
Mast cell tumors (MCT) are the most common skin tumors in dogs. Research shows that MCTs are responsible for around 20% of all skin cancers. MCTs are so common that I teach my young vets to suspect any lump or bump on or just under the skin to be a mast cell tumor until proven otherwise. Scientists don’t understand why this cancer occurs in dogs, but mast cells are made in the bone marrow and migrate to sites in response to inflammation. Fortunately, most MCTs are single and do not metastasize or spread to other parts of the body. Only about 11 to 14% of dogs with an MCT have more than one tumor. MCTs can appear anywhere on the body and are usually slow growing, causing many dog owners to overlook or forget about the crowd until it’s too late. As with many cancers, if diagnosed early and small, MCTs have a better prognosis.
Mast cell tumors are more common in older dogs, typically between the ages of 7 and 9 years. Labradors and Golden Retrievers, Shar-Peis, Boxers, Boston Terriers, American Staffordshire Terriers, Pugs, and French Bulldogs are some breeds that are more likely to develop MCTs, although any dog can develop them at any age.
How to tell if it’s an MCT. acts
Max fit the MCT risk matrix perfectly, and when his mom brought him near the tip of his hind paw that day after the sudden appearance of a pea sprout, we went into action. Whenever a dog has a movable skin tumor, the first thing I do is a fine needle aspiration (FNA). Because MCTs produce large numbers of mast cells in a very small space, it is relatively easy to determine whether a mass is an MCT or not. If you’ve had MCT in the past, or if I’m particularly affected, pretreatment with diphenhydramine (Benadryl) can help reduce the risk of swelling and inflammation after FNA.
The procedure is simple: a needle is carefully inserted into the tumor and cells are aspirated. The sample is placed on a slide for staining and histopathological evaluation. I prefer an initial slide assessment in my clinic. If I see mast cells or other suspicious tissues, I’ll refer the test to a veterinary pathologist. As I peered into Max’s slide, I was greeted by a wall of characteristic small to medium-sized, round, purple-red cells that correspond to mast cells. We stayed overnight for the test.
The next day the laboratory confirmed the diagnosis. We performed regional lymph node FNAs along with chest x-rays to check for possible spread and blood tests. If there was a time for a miracle, it is now.
Time for this miracle
Max’s tests showed no sign of spread. Historically, MCTs have been surgically removed with a wide margin to prevent recurrence. The challenge with many dogs, including Max, was that the hind leg didn’t offer much depth under the cancer or extra skin to close a large excision. In these cases, radiation therapy may be required after surgery. But that was 2020.
It was 2021 and a new MCT treatment for non-metastatic MCT in dogs had just been approved in the US. I had read reports from other countries about Stelfonta and was excited to see it in action. Because it was so new, I referred Max to an oncologist for treatment. The good news is that any veterinarian can give Stelfonta, and it is becoming increasingly available. It’s also affordable, especially when compared to surgery and follow-up care.
Let’s talk about Stelfonta
Tigilanol Tiglate Injection, sold under the brand name Stelfonta, was discovered in the Australian rainforest blushwood plant (Fontainea picrosperma). It was approved by the FDA in November 2020 for the treatment of non-metastatic mast cell tumors in dogs and is only available through a veterinarian.
It is injected directly into the tumor and literally just kills the tumor cells, leaving the surrounding tissue intact. The tumor slowly dissolves and forms what looks like an open wound over the next few weeks. Studies show that around 75% of MCTs are removed with a single injection and 88% with two doses. Sounds like a miracle to me.
And it was. Max received his injection and within a week the cancer turned into what can only be described as “porridge”. The drug manufacturer instructs dog owners to allow the dog to lick and clean it (no E-collars!) And not to bandage or cover the wound. Incredibly, the drug also promotes the healing of normal tissues so antibiotics are not required.
Within two months, Max’s tumor site was completely healed with minimal scarring. Since the treatment is relatively new and we don’t understand what causes MCTs in the first place, it’s too early to say if dogs like Max will have future tumors.
This treatment is best for small, superficial cancers that have not spread. Not all MCTs can be treated with Stelfonta and your veterinarian will determine if your dog is a suitable candidate. The peeling, open wound can be unsettling to some, so be prepared to observe a large wound for a few weeks. It took me a minute to repress my veterinary instincts for bandaging and prescribing.
Max got his miracle. During our last follow-up visit a few months after Stelfonta, I realized that the miracle applies to us too. Max’s mother cheered, noting that she was taking advantage of every day she had with Max and her human family. Overcoming the “word we hate to hear” had given her a new appreciation for the simple joys in life and spending time with loved ones. This is a real miracle now.