Recurrence Rates for Mandibular Fibrosarcoma Associated With Mandibular Canal Invasion Following Mandibulectomy Procedures in Dogs.

Oral fibrosarcoma is a highly invasive tumour with local recurrence rates of up to 57.9% following surgical excision. The optimal surgical margins for long-term local control of oral fibrosarcoma have not been ascertained, especially when tumour invasion into the mandibular canal is present. The objective of this study was to evaluate the recurrence of mandibular fibrosarcoma in dogs following mandibulectomy procedures based on the presence or absence of mandibular canal invasion. Medical records of dogs that underwent a mandibulectomy for fibrosarcoma between January 2005 and December 2023 at 9 veterinary referral centers were reviewed. The size of the tumour, surgical procedure performed, surgical margins obtained, and long-term outcome were recorded. Fisher's exact and Mann-Whitney U tests were used to compare the association between different factors with development of local recurrence. Forty-nine dogs were included. Surgeries performed included segmental mandibulectomy (n = 14), unilateral mandibulectomy (n = 11), bilateral rostral mandibulectomy (n = 9), unilateral rostral mandibulectomy (n = 5), and three-quarter (¾) mandibulectomy (n = 3). Forty dogs had complete histologic margins. Mandibular canal invasion was reported in 14 dogs. Follow-up was available for a median of 493 days postoperatively. Eight dogs were diagnosed with local recurrence. Five dogs with local recurrence had mandibular canal invasion at the initial surgery. No variables evaluated individually were significantly associated with local recurrence. Multivariable logistic regression found the absence of mandibular canal invasion was associated with reduced odds of recurrence (odds ratio, 0.06; 95% confidence interval 0.004-0.835; p = 0.036) when adjusted for the type of mandibulectomy performed and the histopathologic margin status. Further research is needed to determine the optimal surgical margins for dogs with mandibular fibrosarcoma.