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How STELFONTA® Works to Treat Canine Mast Cell Tumors

Efficacy, Safety & Suitability Guide

What is STELFONTA® and who is it for? 

STELFONTA destroys 87% of mast cell tumors with 1 or 2 injections,1 2 so your dog can return to their usual self as soon as possible.   However, not all dogs or tumors are suited to STELFONTA.

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Discuss STELFONTA with your veterinarian

  • Learn which tumors are indicated for STELFONTA
  • Discover whether STELFONTA is right for your dog
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Is STELFONTA Right for Your Dog?

STELFONTA was approved by the FDA6 in 2020 to treat all grades of mast cell tumors, as long as they have not yet spread to other areas of the body (metastasized) and meet the below criteria.6

Ask your vet whether your dog is a suitable candidate for STELFONTA. The tumor should be:

  • No more than 10cm³ (about the size of a walnut in its shell)
  • Easy to reach for injection
  • Anywhere on your dog’s body if it’s on the surface of the skin, and below the skin on your dog’s legs (see illustration below)
Mast cell tumors on the skin surface
Mast cell tumors below the skin surface

RISKS: STELFONTA should not be injected into mast cell tumors that are underneath the skin (subcutaneous) and located above the elbow or hock (e.g. on the body, head, or neck) as necrotic debris from the injected tumor may accumulate in the subcutaneous space, increasing the risk of systemic adverse reactions, including death, from mast cell degranulation.   STELFONTA can treat tumors on the surface of the skin all over the body. Learn about possible Side Effects 

How STELFONTA Works to Treat Mast Cell Tumors

STELFONTA works in three ways to destroy mast cell tumors:  1) disrupts the tumor membrane, 2) cuts off its blood supply, 3) stimulates the dog’s immunity to fight the cancer. The tumor then detaches from the healthy tissue and falls away, leaving a temporary wound and healthy tissue where the tumor once was.

These wounds typically heal within 4 to 6 weeks without intervention. In some cases the wound is extensive and may take longer to fully heal. A wound is just one sign STELFONTA is working and the tumor is destroyed.

Can the tumor be graded after STELFONTA? Because STELFONTA stimulates the immune system to destroy mast cell tumors, it is not possible to send the tumor off for histopathological grading in the same manner as surgically removed tumors. However, cytological grading can be undertaken via a fine needle aspirate prior to treatment if desired.1

1. Cytologic Criteria for MCT grading

MCT treated with STELFONTA - Day 0
Treatment Day
MCT treated with STELFONTA - Day 1
Day 1
MCT treated with STELFONTA - Day 4
Day 4
MCT treated with STELFONTA - Day 7
Day 7
MCT treated with STELFONTA - Day 28
Day 28
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Understand what to expect after STELFONTA injection

American Eskimo dog

Lucy
BREED  American Eskimo
AGE  12 yrs
TUMOR  5cm³ on her thigh

Measurements of mast cell tumor from first diagnosis
American Eskimo with mast cell tumor, treated with Stelfonta
Dog's mast cell tumor, 24hrs after Stelfonta treatment
Mast cell tumor, day 2 post Stelfonta treatment
Mast cell tumor, day 3 post Stelfonta treatment
Mast cell tumor, day 4 post Stelfonta treatment
Mast cell tumor, day 5 post Stelfonta treatment
Mast cell tumor, day 6 post Stelfonta treatment
Mast cell tumor, day 7 post Stelfonta treatment
Mast cell tumor, 8 days after Stelfonta treatment
Mast cell tumor, 9 days after Stelfonta treatment
Mast cell tumor, 14 days after Stelfonta treatment
Mast cell tumor, 28 days after Stelfonta treatment
Mast cell tumor, Day 43 after Stelfonta treatment
Dog's mast cell tumor, 4 months after Stelfonta treatment
Pre Treatment
Day 0 - Treatment
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Day 7
Day 8
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Day 28
Day 43
4 months
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Measurements of mast cell tumor from first diagnosis - thumbnail
Pre Treatment
American Eskimo with mast cell tumor, treated with Stelfonta - htumbnail
Day 0 - Treatment
Dog's mast cell tumor, 24hrs after Stelfonta treatment - thumbnail
Day 1
Mast cell tumor, day 2 post Stelfonta treatment - thumbnail
Day 2
Mast cell tumor, day 3 post Stelfonta treatment - thumbnail
Day 3
Day 4
Day 4
Day 5
Day 5
Day 6
Day 6
Day 7
Day 7
Day 8
Day 8
Day 9
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Day 14
Day 14
Day 28
Day 28
Day 43
Day 43
4 months
4 months
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*Less than 2 hours after treatment an acute inflammatory response is observed with swelling and erythema to the tumor margins and immediate surrounding tissues.

With successful treatment, the tumor will essentially fall away and an empty pocket, or open wound, will remain where the tumor used to be. Don’t worry. This is normal, and healthy new skin will grow and close over.  Most wounds do not need to be covered and heal naturally. 

Within 14 days pet owners say their dogs are back to their pre diagnosis quality of life.

Brooklyn.
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Tips from a dog owner:  Paul’s dog Brooklyn had a tumor on her ear which he elected to treat with STELFONTA.  “I hate the cropped and docked look, so I was excited when I first learned about STELFONTA when researching options and relieved when Dr. Sue Cancer Vet said Brooklyn was a candidate”.  After a successful STELFONTA treatment, Paul reports Brooklyn is back to her healthy, happy, sassy self, and shares his tips for the journey:

  • Do your research
  • Ask questions and get the facts from your veterinarian
  • Don’t let the pictures scare you off, the wound is created when the tumor falls away and heals on its own in most cases
  • Precisely follow instructions for medications
  • Be prepared for a bit of a mess, lay down some old sheets where they sleep
  • The first few days are the hardest, but be patient
  • Most of all, love and support your pet. They need you now more than ever

Prepare your dog for their treatment with practical tips.

Still looking for something?

Prepare for STELFONTA treatment
Care after STELFONTA
STELFONTA Discussion Guide
References
  1. US STELFONTA ® (tigilanol tiglate injection) packaging insert. 2025
  2. De Ridder TR, et al. J Vet Intern Med 2020 ;doi :10.1111/jvim.15806.
  3. Jones P et al. 2020. J Vet Internal Medicine. https://doi.org/10.1111/jvim.16018
  4. Melo SR et al. VCS abstract 2019.
  5. Campbell J et al. Wound Rep Reg 2014;22:A73-A100.
  6. https://www.fda.gov/news-events/press-announcements/fda-approves-first-intratumoral-injection-treat-non-metastatic-mast-cell-tumors-dogs

FDA-CVM WARNING: SEVERE WOUND FORMATION IN HUMANS; EXTENSIVE WOUND FORMATION, MAST CELL DEGRANULATION, AND DEATH IN DOGS DUE TO MAST CELL DEGRANULATION

Human Safety

  • Accidental self-injection of STELFONTA® may cause severe wound formation. To decrease the risk of accidental self-injection, sedation of the dog may be necessary (see Dosage and Administration, Human Warnings and Adverse Reactions).

Dog Safety

  • Always administer a corticosteroid, an H1 receptor blocking agent (e.g. diphenhydramine), and an H2 receptor blocking agent (e.g. famotidine) when treating with STELFONTA to decrease the potential for severe systemic adverse reactions, including death, from mast cell degranulation (see Contraindications and Dosage and Administration).
  • Do not inject STELFONTA into subcutaneous mast cell tumors located above the elbow or hock (e.g. on the body, head, or neck). This may result in accumulation of necrotic debris in the subcutaneous space increasing the risk of systemic adverse reactions, including death, from mast cell degranulation (see Contraindications, Warnings and Adverse Events).
  • Treatment with STELFONTA has been associated with cellulitis and severe tissue sloughing extending away from the treated site resulting in extensive wounds that require additional treatment and prolonged recovery times (see Warnings, Precautions and Adverse Events).

IMPORTANT SAFETY INFORMATION
Formation of wounds, possibly extensive, is an intended and likely response to treatment with STELFONTA along with associated swelling, bruising and pain; these wounds are expected to heal. Appropriate pre- and post-treatment medications must be given, including a corticosteroid plus blocking agents for both H1 and H2 receptors, in order to decrease the potential for severe systemic adverse reactions, including death, from mast cell degranulation.

Full prescribing information