Medical Oncology: Stelfonta®

What Is Stelfonta?

Stelfonta is used to treat mast cell tumors in dogs. Stelfonta is given as one injection, directly into the tumor. It destroys the cancer cells and starves the cells’ blood supply. This creates a wound at the injection site. The wound is left open and will heal on its own. The process typically takes 4-6 weeks.

What Types of Tumors Can Be Treated With Stelfonta?

Stelfonta can be used on mast cell tumors in the skin anywhere on the body. It can be used in tumors underneath the skin in certain locations.

The overall extent of wound formation and time to heal is variable. It usually relates to the size and/or location of the tumor.

What Happens To My Pet?

The Four Stages of Treatment

1. Pre-treatment: Dogs receive medications a few days before and after treatment with Stelfonta. These are given to reduce the chance of severe reactions.
2. Treatment: Stelfonta is injected into the tumor. Dogs may need light sedation to help this. The most common side effects are the formation of wounds, lameness, vomiting, diarrhea, and low levels of protein in the blood. You may notice changes in the tumor within 4 hours of the injection. This includes swelling and color changes. Dogs may be prescribed pain medication.
3. Tumor breakdown (Days 1-7 after injection): The tumor will show signs of bruising and swelling and leaking of fluid. As the tumor is destroyed, a red “pocket” will form (wound). This is usually left to heal on its own. During this time it is important to monitor your dog for signs of excessive pain, vomiting/diarrhea, loss of appetite, trouble breathing, or any other unusual activity or signs. You will continue to administer medications to your pet.
4. Wound healing (weeks 2-4): Healthy new skin will grow over the wound. Fur usually grows over the area as well. Some dogs require a second Stelfonta injection to treat the tumor.

What Are The Pros/cons Of Treatment With Stelfonta?

Pros	Cons
Does not require anesthesia	Cannot obtain a grade for the tumor
Outpatient procedure	May require more than one treatment or not work at all
Less expensive than surgery	Could create a wound that requires surgical intervention
Useful for tumors in locations where surgery is not possible or difficult	Should not be used in dogs with metastatic disease

There are many good reasons to pursue treatment with Stelfonta. The biggest concern is that we cannot learn the grade of the tumor. The grade tells us the most about the chance that the tumor will regrow and spread. This is risky for some dogs.

Much more information on Stelfonta can be found at www.stelfonta.com, including pictures of dogs with mast cell tumors treated with Stelfonta.