Reassigned surgical margins after neoadjuvant chemotherapy results in low local recurrence in dogs with mast cell tumours.

Abstract

Neoadjuvant chemotherapy (NAC) is delivered before surgery to allow less extensive tumour resection, but the optimal surgical margin width after NAC is unknown. The aim of this study was to determine the impact of reassigned margins on local recurrence after NAC in dogs with mast cell tumours (MCTs). A retrospective analysis was conducted for dogs with MCTs undergoing NAC consisting of vinblastine and prednisolone, subsequent tumour resection and lymphadenectomy, and a minimum follow-up of 6 months. Surgical margins were reassigned based on the size of the MCT after NAC. Pre- and post-NAC measurements of MCTs were recorded. The margin status was assessed with a combined radial and tangential sectioning technique; pre-NAC MCT cytograde and lymph node (LN) cytological status were compared with the Kiupel grade and Weishaar stage, respectively. Twenty-two dogs were included. MCT shrinkage after NAC consistently occurred, with a median reduction rate of 40.4% (range 5%-94.5%). Margins were complete in 15 of 22 dogs, and two MCTs and three LNs appeared histologically downgraded and downstaged, respectively. Two (9.1%) MCTs recurred. The limitations of this study were the small sample size and relatively short follow-up. NAC leads to shrinkage of canine MCTs, with the resulting reassigned surgical margins being associated witha low recurrence rate.