Evaluation of scar revision after inadequate primary excision of cutaneous mast cell tumors in 85 dogs (2000-2013).

OBJECTIVE To determine the frequency of residual tumor, and factors associated with local recurrence and disease progression in dogs with incompletely excised mast cell tumors (MCT) following scar revision surgery. STUDY DESIGN Retrospective study. ANIMALS Eighty-five dogs. METHODS Medical records from January 2000 to April 2013 were reviewed. Dogs with scar revision surgery after incomplete primary MCT excision were included. Recorded were signalment; initial tumor size, location and grade; time interval between primary excision and scar revision surgery; presence of MCT in the resected scar; local recurrence, lymph node metastasis, systemic metastasis, and cause of death. RESULTS Eighty six tumors in 85 dogs were studied. Residual MCT was found in 23 (27%) resected scars. Seven (8%) scars with residual MCT had incomplete or narrow margins. Follow-up was available for 68 dogs (69 tumors; median 403 days; range 4-2939). Local recurrence was reported in three (4%) dogs at 212, 555, and 993 days. Disease progressed in 10 dogs (14.5%) with regional or systemic metastasis at a median of 207 days (64-1583). Margin status and presence of MCT in the resected scar were not associated with local recurrence or disease progression. Lymph node metastasis (p = .004), locoregional recurrence (p = .013), and disease progression (p = .001) were significantly more likely in Grade III tumors. CONCLUSION Twenty-seven percent of resected scars contained residual MCT, but recurrence was uncommon after surgical revision. CLINICAL SIGNIFICANCE Clinicians should primarily consider tumor grade when estimating the likelihood of local recurrence and disease progression and determining the need for ancillary treatment of MCT after scar resection.