FDA approves first intratumoral Injection to treat mast cell tumors in dogs

Today, the U.S. Food and Drug Administration approved Stelfonta (tigilanol tiglate injection) to treat dogs with non-metastatic, skin-based (cutaneous) mast cell tumors (MCTs). The FDA is also approving Stelfonta to treat non-metastatic MCTs located under the dog’s skin (subcutaneous), in particular areas of a dog’s leg.  Stelfonta is injected directly into the MCT (intratumoral injection). Stelfonta works by activating a protein that spreads throughout the treated tumor, which disintegrates tumor cells.

“This is the first approval for an intratumoral injection to treat non-metastatic mast cell tumors in dogs,” said Steven M. Solomon, D.V.M., M.P.H., director of the FDA’s Center for Veterinary Medicine. “This approval provides an additional treatment option to help treat local mast cell tumors on or under the skin in dogs.”

MCTs are the most common malignant skin tumor in dogs, and usually present as a lump on or under the skin. Full surgical removal of MCTs can be difficult when tumors are located in certain areas, such as the leg. When MCTs are not fully removed, the remaining malignant cells can start to grow and spread rapidly. Stelfonta offers a novel way to treat non-metastatic MCTs as the only approved intratumoral injection.

Stelfonta is available only by prescription due to the professional expertise required to diagnose MCTs, properly administer the injection, provide adequate instructions for post treatment care, and monitor the safe use of the product, including treatment of any adverse reactions. The label for Stelfonta carries a boxed warning for human safety because of the risk of severe wound formation from accidental self-injection or needle stick injuries. The boxed warning also includes several statements regarding the safe use of Stelfonta in dogs, including: Stelfonta should always be given with a corticosteroid, an H1 receptor blocking agent and an H2 receptor blocking agent, to decrease the risk of severe systemic adverse reactions, including death, from mast cell degranulation. Veterinarians should provide the client information sheet to pet owners for important information about Stelfonta and how to care for their pets after they have been given the drug.

The safety and effectiveness of Stelfonta was established in a study of 118 dogs with a measurable cutaneous or a subcutaneous MCT on the lower leg. Eighty of those dogs were treated with Stelfonta and 38 were in an untreated control group. The dogs were followed and tumor response was assessed almost a month after their first injection. The complete remission rate after treatment with Stelfonta was 75%. Eighteen dogs in the group  treated with Stelfonta that didn’t have their treated tumor completely disappear were retreated with Stelfonta a second time about a month after the first treatment, and approximately a month after receiving their second treatment, 44% of these dogs had their tumor disappear completely. Dogs in the untreated control group were treated with Stelfonta for the first time a month after the study began, and 62% of those dogs had their tumor disappear.

Stelfonta should not be used to treat subcutaneous MCTs located above the elbow or hock. Stelfonta may cause extensive wound formation at the tumor site, including cellulitis and severe tissue sloughing. The most common adverse reactions associated with Stelfonta were wound formation at the tumor site and injection site reactions, such as pain, swelling, reddening of the skin, bruising, thickening, scarring, and death of some cells in the tissues. Lameness in the treated leg, vomiting, diarrhea, hypoproteinemia, and hypoalbuminemia also occurred. These were likely due to the wound healing process and the drug’s effect on the tumor. Most wounds gradually reduced in size or completely resolved. A small number of dogs developed extensive wounds with cellulitis, bacterial skin infections, or severe tissue sloughing that extended away from the treated tumor which led to a prolonged recovery time and additional wound care. 

Stelfonta will be marketed in the U.S. by Virbac.

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Stelfonta