Use of histologic margin evaluation to predict recurrence of cutaneous malignant tumors in dogs and cats after surgical excision

Objective. To assess the usefulness of the histologic evaluation of surgical margins in predicting local recurrence in canine and feline malignant skin tumors, and the influence of clinicopathologic parameters (tumor size, type and grade) on method accuracy. Design - Prospective case series. Animals - 60 client-owned dogs (40) and cats (20). Procedures - 60 canine and feline surgically-removed skin tumors (20 soft tissue sarcomas, 20 mast cell tumors and 20 carcinomas) were examined. Margins were classified as clean, close (< 2 mm) or infiltrated. Histologic grade was assessed in sarcomas and mast cell tumors. Patients were monitored for 24 months after surgery and recurrence-free intervals were recorded. Results - Margins were clean in 29/60 cases (48%), close in 11/60 (18%) and infiltrated in 20/60 (33%). Tumors recurred in 27 cases (45%), with a mean recurrence-free interval of 229 days (range, 30-661). Recurrence rate was 80% among infiltrated margins (16/20), 73% among close margins (8/11), and 10% among clean margins (3/29). Method accuracy was 94% for carcinomas, 87% for sarcomas and 76% for mast cell tumors. Conclusions and Clinical Relevance – The histologic assessment of the margin status is a useful prognostic indicator for postsurgical monitoring and adjuvant therapeutic planning of malignant skin tumors. Nevertheless, the method is more likely to generate false positives in grade I mast cell tumors. Because of generally long recurrence times, postsurgical surveillance should be extended to at least 2 years. There should be no distinction in the clinical approach to either close or infiltrated margins.