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.