Mast Cell Tumors in Dogs: Non-Surgical Treatment—Stelfonta®

A mast cell tumor is a cancer of mast cells, a type of immune cells involved in allergic response.

Even though they can form internally, you’re most likely to find a mast cell tumor (MCT) when you detect a bump on your dog’s skin.

Some breeds are especially susceptible to developing these tumors, such as:

  • Boxers
  • Bull Terriers
  • Boston Terriers
  • Labrador Retrivers

Mast cell tumors can behave and look in many different ways. MTCs can be visually similar to many other tumors. Not all skin masses are cancerous, but you cannot judge a tumor by its appearance. The only way to identify a lump is to take a sample and look at the cells under a microscope—fine needle aspirate followed by cytology.

Other symptoms and complications of mast cell tumors might include:

  • weight loss
  • loss of appetite
  • lethargy
  • vomiting
  • diarrhea
  • black, tarry stools
  • anaphylaxis

Further information: Canine Mast Cell Tumors

Mast Cell Tumors in Dogs: Non-Surgical Treatment

Mast cell tumor treatment

The golden standard treatment for mast cell tumors has been surgical removal—Many MCTs are curable with surgery.

Other treatments might become necessary depending on the grade and whether the surgeon could remove the entire tumor with clean margins.

For example, if a grade III tumor cannot be removed or there is evidence of spread, your veterinarian might recommend chemotherapy.

Radiation therapy is a consideration in certain cases.

All of that is quite invasive, and successful surgery might be tricky in locations where there isn’t enough tissue to get clean margins. For instance, that was a case with JD’s MTC. We did manage to get it removed with clean margins, but there was no way to close the wound, and we had to resort to a skin graft.

A new breakthrough in the treatment of mast cell tumors in dogs

What if your dog’s MCT could be treated by an injection? Enter Stelfonta®.

Stelfonta®, originally conceived in Australia, is an intra-tumoral therapy that the FDA approved in late 2020. It has shown good promise in the treatment of non-metastatic skin mast cell tumors in dogs.

How does it work?

Stelfonta® contains a compound extracted from the seed of an Australian rainforest shrub. The compound is injected directly into the tumor, stimulating a local immune response that leads to the destruction of the tumor and its blood supply. The dead tumor then sloughs off while the healthy tissue quickly heals.

Mast Cell Tumors in Dogs: Non-Surgical Treatment—Stelfonta®--healed tumor
Healed mast cell tumor after Stelfonta® treatment. Photo Dr. Sue Cancer Vet

You can see photos documenting the entire process here.

Is it effective?

In a field study of 123 dogs, the treatment removed 75% of the treated tumors by day 28. 93% of those tumors have not returned by day 84.

While some dogs still might need surgery, this treatment is a promising alternative starting point. I certainly wish it was available when our dog was diagnosed with MCT. The surgery did cure his cancer, but it took a long time for his surgical wound to heal. On top of that, he not only had the wound where the tumor was removed but also on his chest from which the veterinarian harvested the skin graft.

For further up-to-date information, follow Dr. Sue Ettinger’s YouTube Channel. I’ll be watching.

Related articles:
What Is That Bump on My Dog: Canine Lumps, Bumps, and Growths
A Primer On Mast Cell Tumors
Canine Mast Cell Tumors: JD’s Mast Cell Tumor Diagnostics, Strategy, and Treatment
Mast Cell Tumor Diagnosis: JD’s Biopsy Results Revealed Mast Cell Tumor
Mast Cell Tumor Treatment: JD’s Mast Cell Tumor— Surgery and Pathology Report

Further reading:
Canine Mast Cell Tumors

Categories: CancerConditionsDog health advocacyLumps and bumpsMast cell tumors (MTC)Stelfonta®Symptoms

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Jana Rade

I am a graphic designer, dog health advocate, writer, and author. Jasmine, the Rottweiler of my life, was the largest female from her litter. We thought we were getting a healthy dog. Getting a puppy from a backyard breeder was our first mistake. Countless veterinary visits without a diagnosis or useful treatment later, I realized that I had to take Jasmine's health care in my own hands. I learned the hard way that merely seeing a vet is not always enough. There is more to finding a good vet than finding the closest clinic down the street. And, sadly, there is more to advocating for your dog's health than visiting a veterinarian. It should be enough, but it often is not. With Jasmine, it took five years to get a diagnosis. Unfortunately, other problems had snowballed for that in the meantime. Jasmine's health challenges became a crash course in understanding dog health issues and how to go about getting a proper diagnosis and treatment. I had to learn, and I had to learn fast. Helping others through my challenges and experience has become my mission and Jasmine's legacy. I now try to help people how to recognize and understand signs of illness in their dogs, how to work with their veterinarian, and when to seek a second opinion. My goal is to save others the steep curve of having to learn things the hard way as I did. That is the mission behind my blog and behind my writing. That is why I wrote Symptoms to Watch for in Your Dog, which has turned out being an award-winning guide to dog owners. What I'm trying to share encompasses 20 years of experience.

  1. My previous Persian cat, Praline, had a mast cell tumor beside her nose that was surgically removed. I thought everything was fine until she died from cancer a year later that was in her digestive tract. I hope this medication is studied more and something can be made available for cats.

  2. This was really interesting read. I have never had a dog that was diagnosed with MCT, but I know of multiple friends that have had to navigate this. The idea that some cases may be solved with an injection is a HUGE step in the right direction! I can only imagine how relieved this would leave the dog owners in these situations!

  3. Great post and I love the idea that you can treat them without surgery as it is less stressful for the dogs plus the Moms, thanks for this information

  4. This is great news! Although I’m grateful that surgery is an option, a non invasive procedure is so much better!

  5. This is awesome! A non surgical, non invasive way to treat mast cell tumors in dogs. Thanks for sharing this great information.
    Love & Biscuits,
    Dogs Luv Us and We Luv Them

  6. It is so great that they are starting to come up with more (and better) ways to treat things like tumors in our pets. I had a friend that had to do chemotherapy for her cat and it was stressful to them both.

  7. Wow, this is amazing news to hear. I had almost given up on medicine being able to do anything beyond palliative care but then this. I am so impressed, especially as the figures for ‘removal’ look so high. This is no longer the frightening news it might have been.

    A fantastic post and it muse feel great to be able report something so positive.

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