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

Background:Neoadjuvant chemotherapy (NAC) is delivered before surgeryto allow less extensive tumour resection, but the optimal surgical marginwidth after NAC is unknown. The aim of this study was to determine theimpact of reassigned margins on local recurrence after NAC in dogs with mastcell tumours (MCTs). Methods:A retrospective analysis was conducted for dogs with MCTs under-going NAC consisting of vinblastine and prednisolone, subsequent tumourresection 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 wasassessed with a combined radial and tangential sectioning technique; pre-NAC MCT cytograde and lymph node (LN) cytological status were comparedwith the Kiupel grade and Weishaar stage, respectively. Results:Twenty-two dogs were included. MCT shrinkage after NAC consis-tently 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 LNsappeared histologically downgraded and downstaged, respectively. Two(9.1%) MCTs recurred. Limitations:The limitations of this study were the small sample size andrelatively short follow-up. Conclusion:NAC leads to shrinkage of canine MCTs, with the resultingreassigned surgical margins being associated with a low recurrence rate.