Prognosis following surgical excision in canine and feline malignant skin tumors: the role of the histological evaluation of margins.

Wide surgery represents the best therapy for skin tumors, although hampered by local recurrences after incomplete removal. As the clinical assessment of tumor size rarely corresponds to its actual extension, the completeness of surgery can be effectively determined only by the histological evaluation of excision margins. To assess the efficacy of the histological evaluation of margins in predicting the development of local recurrence, 50 canine and feline surgically-removed skin tumors (21 MCTs, 18 soft tissue sarcomas, 11 carcinomas) have been examined. Margins were judged as clean, clean but close (tumor cells < 2 mm from margins) or infiltrated. Histological grade was assessed in sarcomas and MCTs. Tumor recurrence-free intervals (RFIs) at 1 and 2 years were recorded. Margins were infiltrated in 19/50 cases (38%), clean but close in 9/50 (18%), and clean in 22/50 (44%). Recurrence occurred in 19 cases. Mean RFI was 233 days (range: 31-661). Recurrence rates were 68.42% (infiltrated margins), 44.44% (clean but close margins), and 9.09% (clean margins). The method accuracy improved with the extension of the follow-up period, and was highest for carcinomas (100%), intermediate for sarcomas (89%) and lower for MCTs (78%), due to actual difficulties in distinguishing if mast cells found on margins are normal or neoplastic. Histological evaluation of margins is a good predictor for tumor recurrence, although more likely to generate false positives in MCTs. Because of generally long recurrence times, post-surgical surveillance should be extended to at least 2 years. Tumor grade influences RFI but not the method accuracy.