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Have you ever treated large mast cell tumors with CCNU to shrink them before attempting removal?
A. I have not used CCNU, or lomustine, before excising larger mast cell tumors, partly because no studies have evaluated CCNU's efficacy for this indication. Also, marked side effects can occur, particularly neutropenia, which makes it a poor match for surgical patients. Neoadjuvant therapy with prednisone has been studied and is effective for decreasing mast cell tumor size in dogs.1
I usually consider prednisone therapy preoperatively in dogs when the mast cell tumor is either too large to excise with acceptable margins (minimum 3 cm) or the mass is located in an area where the margins are anatomically limited (e.g. perianal, distal limb). I mark the mass with an indelible pen before treatment so the response can be measured. Prednisone is typically given for two weeks. Duration of treatment may be adjusted based on the size and response of the mass. Radiation has also been evaluated as a pretreatment of mast cell tumors in cats2 and dogs. If you have any doubt about the feasibility of a wide excision, consider referral to a board-certified surgeon.
Jenifer Newton, DVM, MS, DACVS
Answer provided by Jenifer Newton, DVM, MS, DACVS, Saint Francis Veterinary Specialists, Decatur, Ga.
1. Stanclift RM, Gilson SD. Evaluation of neoadjuvant prednisone administration and surgical excision in treatment of cutaneous mast cell tumors in dogs. J Am Vet Med Assoc 2008;232(1):53-62.
2. Turrel JM, Farrelly J, Page RL, et al. Evaluation of strontium 90 irradiation in treatment of cutaneous mast cell tumors in cats: 35 cases (1992-2002). J Am Vet Med Assoc 2006;228(6):898-901.