Mast cell tumors (MCTs) are the most common type of malignant skin cancer in dogs, accounting for about 7% to 21% of all skin tumors. Since the biological representation varies greatly from dog to dog and even from tumor to tumor, this form of canine neoplasia is often referred to as “complicated” and “challenging”.
What are the treatment options for dogs with mast cell tumors?
In the June 2019 issue of the Whole Dog Journal, we highlighted some potential treatments for dogs with mast cell tumors that are currently being explored. Two of these treatment options showed positive progression.
Nanoshell technology and laser ablation for the treatment of mast cell tumors
Companion Animal Health continues to explore the use of nanoshell technology and laser ablation to treat mast cell tumors. The first data from a study presented to the American College of Veterinary Internal Medicine (ACVIM) in 2018 showed that 100% of patients responded to therapy, with 67% maintaining remission. The treatment combines laser light therapy with gold nanoparticles, which have shown increased sensitivity to visual and near infrared light.
The nanoparticles administered by intravenous injection accumulate in cancerous tissues. The tumor is then irradiated with laser light, which causes the electrons in the nanoparticles to pass into an excited state that releases energy through the generation of heat. This leads to overheating of the regional tissue with subsequent local cell death and destruction. This nonsurgical, one-time treatment option can allow veterinarians to shrink and stop tumor growth in dogs that have masses in regions where surgery may not be possible or completely successful and limited to no complications.
The FDA recently approved STELFONTA
In November 2020, the U.S. Food and Drug Administration’s Center for Veterinary Medicine (CVM) approved QBiotic’s STELFONTA for the pharmaceutical treatment of all types of non-metastatic mast cell tumors in dogs. STELFONTA is a novel veterinary anti-cancer product that contains the tigilanol tailgate (also known as EBC-46), a compound extracted from the seeds of Fontaine Picrosperma (commonly known as the brushwood tree) found in the rainforest of North Queensland, Australia. The tigilanol tailgate (TT) triggers the action of enzymes known as protein kinase C (PKC). When injected directly into the tumor, it causes a rapid but highly localized immune response that disrupts the blood supply to the tumor, thereby inducing tumor cell death. This process leads to the destruction of the tumor mass, followed by rapid healing of the resulting wound with minimal scarring.
In a randomized controlled clinical two-phase study of 123 dogs with cytologically diagnosed MCT, researchers found that a single TT treatment resulted in a complete response (tumor completely disappeared) in 75% of cases after 4 weeks (phase 1). Those dogs that had not achieved tumor resolution after 4 weeks were treated with a second dose and approximately half responded (phase 2), increasing the overall response rate to 87%. Of the treated dogs with complete responses available for follow-up, 100% were still disease free at the treated tumor site after 8 weeks, and 96% remained disease free after 12 weeks.
STELFONTA has been approved for the treatment of non-metastatic cutaneous mast cell tumors and non-metastatic subcutaneous mast cell tumors at or distal to the elbow or ankle in dogs. The tumor size must not exceed 10 cm. A regimen of corticosteroids and antihistamines / H2 blockers must be given to reduce the risk of severe systemic side effects from mast cell degranulation. The treatment is administered by a veterinarian with a single injection directly into the tumor; A second dose can be given if the tumor tissue remains four weeks after the first treatment and the surface of the remaining mass is intact. The most common side effects were sore formation (although expected due to the destruction of the tumor), reactions at the injection site such as mild to moderate pain at the time of injection, redness / swelling / bruising / thickening of the skin, pain and / or lameness in the treated area Extremity, vomiting, diarrhea and low blood albumin levels. These adverse events were usually mild, quickly resolved, and usually directly related to the mode of action of TT. Overall, it has been shown that this innovative treatment is well tolerated and enables dogs to regain their quality of life quickly.
STELFONTA is being launched in the US by global animal health company Virbac and will be available to veterinary oncologists for the next several months. Availability for veterinarians in primary care will follow.