Stelfonta for Dogs: A Medication for Mast Cell Tumors When Surgery Isn’t an Option

Mast cell tumors are one of the most common forms of skin cancer in dogs. These tumors require fast treatment because they can be aggressive and spread to other parts of the body. 

Stelfonta (tigilanol tiglate) is a relatively new treatment option for canine mast cell tumors. It is primarily used to treat tumors that cannot safely be removed surgically. 

Keep reading to learn more about this Stelfonta for dogs.

Stelfonta for dogs at a glance

What is Stelfonta for dogs, and how does it work?

Stelfonta is a relatively new cancer medication for dogs. It received FDA approval in 2020.

Stelfonta is a protein kinase C activator. This means that it activates an enzyme (a natural substance in the body) called protein kinase C. Because of this, when Stelfonta is injected into a tumor, it causes:

• Inflammation of the tumor

• Disrupted tumor blood flow

• Tumor cell death

These effects can be used to eliminate some mast cell tumors.

What is Stelfonta used for in dogs?

Stelfonta is used to treat mast cell tumors in dogs. It is primarily used to manage mast cell tumors that cannot be removed surgically. 

The first-choice treatment for mast cell tumors is surgery. But mast cell tumor surgery requires a veterinarian to remove a lot of the tissue around the tumor. This ensures that all tumor cells are completely removed. This is easy on some parts of a dog’s body, like the torso. But removing enough tissue isn’t possible on other parts, like the legs and muzzle.

EXPERT PICKS: WHAT TO READ NEXT

• A firsthand account of Stelfonta (tigilanol tiglate) for dogs: Read how one dog owner treated her pup’s mast cell tumor using Stelfonta — and why she says it was worth it.

• Mast cell tumors: If your dog was diagnosed with a mast cell tumor, here’s everything you need to know about this common skin cancer.

• Other dog skin cancers: Mast cell tumors are just one type of skin cancer that can affect dogs. Here are some other common ones your veterinarian may want to rule out.

When a dog’s mast cell tumor is in a location where it’s difficult to remove enough tissue, a veterinarian may suggest Stelfonta. In one study, Stelfonta successfully removed mast cell tumors in about 75% of dogs with a single treatment.

What is the typical dosage of Stelfonta for dogs, and how is it given?

Stelfonta is given to dogs as an injection at the veterinarian’s office. 

Two days before your dog receives the injection, you will give them pretreatment medications at home. These medications typically include:

• A steroid, such as prednisone

• An antihistamine, like diphenhydramine

Pretreatment medications reduce the risk of side effects associated with Stelfonta treatment. 

After 2 days of pretreatment, you will take your dog to the veterinarian for the Stelfonta injection. At the appointment, your veterinarian will do the following: 

• Shave the hair from the tumor and surrounding area

• Measure the tumor and calculate its volume

• Determine the correct Stelfonta dosage, based on the tumor’s size

• Inject Stelfonta directly into your dog’s tumor 

• Apply a bandage

Some dogs need sedation for a Stelfonta injection. Your dog must hold very still so that all of the medication is injected directly into their tumor.

Your dog may be sent home with an e-collar (cone) after receiving Stelfonta. This will keep them from licking their tumor and wound in the coming days and weeks. 

After your dog receives the Stelfonta injection, you will continue their steroid and antihistamine treatment for 1 week. Your veterinarian will also prescribe them an antacid, like famotidine. These post-treatment medications reduce the risk of side effects associated with Stelfonta. 

Some dogs need only one Stelfonta injection. Other dogs may need more than one.

What are the common side effects of Stelfonta in dogs?

The most common side effect of Stelfonta in dogs is an open, draining wound at the mast cell tumor site. This wound is a result of the tumor dying, so it means the medication is working. It usually forms between 3 to 7 days after an injection and is a normal part of Stelfonta treatment. 

The wound may initially be larger than the tumor. But it will shrink over time. The healing process usually takes 4 to 6 weeks. Stelfonta’s website provides examples of post-treatment wounds at different stages of healing if that’s helpful for you to see. 

Your veterinarian will prepare you for what to expect during treatment. They will also help you monitor your dog’s progress.  

Less common side effects that may occur with Stelfonta include: 

• Swelling at the injection site

• Bruising at the injection site

• Pain and discomfort

• Limping (when tumors on the leg are treated)

• Infection of the open wound 

• Enlarged lymph nodes

• Lack of energy

• Loss of appetite

If you notice any concerning side effects, talk to your veterinarian. 

What are the most serious risks of Stelfonta for dogs?

The most serious risk of Stelfonta for dogs occurs when the mast cell tumor dies. As a mast cell tumor dies, it releases inflammatory signals that can cause negative effects in dogs. This process is called degranulation.

You will give your dog medications before and after their Stelfonta injection. The medications should help protect your dog from these inflammatory signals. But in rare cases, mast cell tumor degranulation can cause:  

• Vomiting

• Diarrhea

• Weight loss

• Pale gums

• Collapse (shock)

• Stomach ulcers 

If your dog becomes seriously ill after receiving Stelfonta, seek veterinary care immediately. If your veterinarian’s office is closed, contact an emergency pet clinic. Immediate treatment may be needed.

Does Stelfonta interact with any other dog medications?

At this time, there are no known interactions between Stelfonta and other medications. But Stelfonta is a relatively new treatment. We may discover medication interactions as it’s used to treat more dogs.

To minimize the risk of interactions, make sure your veterinarian knows about any medications your dog is taking. This includes: 

• Prescription medications

• Over-the-counter medications

• Nutritional supplements  

Knowing your dog’s full medication history can help your veterinarian reduce the risk of interactions.

What should you do if your dog misses a dose of Stelfonta?

Stelfonta is given as a one-time injection in a veterinary clinic. If you miss your dog’s appointment, your visit will be rescheduled for another day or time. 

Give your dog their pretreatment medications as directed. If you miss a dose of one of these medications in the days leading up to your dog’s Stelfonta injection, contact your veterinarian. They may postpone your dog’s treatment. 

Your dog’s post-treatment medications will also help reduce side effects. If you miss a dose of your dog’s steroid, antihistamine, or antacid after their injection, give them the medication as soon as you remember. Then, wait the recommended amount of time to give them their next dose. Do not give your dog a double dose of medication. 

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Written by:

Catherine Barnette, DVM

Catherine Barnette, DVM, is a small animal veterinarian with 14 years of experience providing preventive care, medical workups, and surgical services in a number of general veterinary practices. She also served on her county's board of health for several years and taught biology laboratories for college students.

Edited by:

Renée Fabian, MA

Renée Fabian is the senior pet health editor at GoodRx. She’s worked for nearly 10 years as a journalist and editor across a wide range of health and well-being topics.

Reviewed by:

Ghanasyam Bey, DVM

Ghanasyam Bey, DVM, is from Cleveland, Ohio, and attended Princeton University for undergraduate studies. After a year of biology research at Duke University, he attended Ohio State College of Veterinary Medicine.

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