What’s New in the Treatment of Mast Cell Tumors

January 31, 2022

Annie Galloway, DVM, MS, DACVIM (Oncology)

STELFONTA® (tigilanol tiglate injection) by Virbac

This is an FDA-approved intratumoral injection for the local treatment of non-metastatic mast cell tumors in dogs. The goal of the treatment is to cause rapid, local inflammation eventually leading to tumor cell death and necrosis (typically by day 7). This creates open wounds that heal by second intention, which can take some time. Second dosages can be applied 28 days later. In their pivotal study, 75% of dogs had a complete remission of the local tumor after one dose and 87% of dogs had complete remission of the local tumor after 2 doses. 89% of dogs were found to be disease-free (at the site of injection) at 12 months. 57%, 78%, and 96% of wounds were fully healed at day 28, day 42, and day 84, respectively.  

STELFONTA® can be used for non-metastatic cutaneous mast cell tumor anywhere on the body and non-metastatic subcutaneous mast cell tumors located at, or distal to, the elbow or hock. Tumors must be smaller or equal to 10 cm³ in volume and must be accessible to intratumoral injection. Do not exceed 5 mL per dog (regardless of the tumor size) and minimum dose is 0.1 mL (regardless of tumor size). Management includes concurrent pain medications and ongoing wound management/bandage changes. Pre- and post-treatment medications (including prednisone, famotidine, and diphenhydramine) are important for reducing systemic adverse events secondary to mast cell degranulation. Limitations would include inability to know tumor grade, which can have significant impact on patient outcome and recommendations for adjuvant chemotherapy. Options would be to request a cytologic grade (Camus et al Vet Path 2016) of the mast cell tumor to get a better idea of its potential biologic behavior that may help better inform clients. An incisional biopsy could also be considered for tumor grade and possible c-kit mutation status, yet the incision should be healed prior to injection (which is not always feasible).