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 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.

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