Reductions in margin length after excision of grade II mast cell tumors and grade I and II soft tissue sarcomas in dogs

Abstract

Objective: Quantify changes in the circumferential lengths of surgical margins of resected canine mast cell tumors (MCT) and soft tissue sarcomas (STS) between the time of collection and histopathology.Study design: Prospective, hypothesis-driven, clinical study.Sample population: Two hundred and thirty-seven margins from 69 excised tumors (50 MCT and 19 STS) in 51 client-owned dogs. Methods:The lengths of surgical margins were recorded (eg, cranial, caudal, dorsal, and ventral) for each tumor at 5 time points: intraoperatively (in vivo), immediately after excision (ex vivo), after formalin fixation (postfixation), once mounted on glass slides (subgross), and as histologically tumor-free margins (HTFMs).Results: Compared to in vivo dimensions, the length of surgical margins at each processing step (ie, ex vivo, postfixation, subgross, and HTFM) was reduced by a median of 3.0, 5.0, 6.0, and 8.8 mm for MCT; 2.5, 2.0, 5.0, and 5.0 mm for STS. All processing steps resulted in significant reductions among MCT samples (P < .0001), except between postfixation vs subgross, and for STS samples (P < .0001), except between ex vivo vs postfixation and subgross vs HTFM. The maximum reduction in the total length of margins (from in vivo to HTFM) was 29.6 and 24.2 mm for MCT and STS, respectively.Conclusion: Surgical margin length reductions occur due to a combination of physical factors (eg, tissue elasticity, myofibril contraction, and histologic processing) and biological factors (eg, microscopic tumor infiltration into the grossly normal surgical margin).Clinical significance: These data provide information relevant to evidence-based surgical planning and may influence patient morbidity in the most commonly encountered cutaneous malignancies of dogs.

Histologic margins and the residual tumour classification scheme: Is it time to use a validated scheme in human oncology to standardise margin assessment in veterinary oncology?

“…Shrinkage of the tumour specimens can result in tumour cells being closer to the surgical resection margins than in vivo. The majority of this specimen shrinkage occurs immediately after surgical resection because of the effects of myofibril contractility and tissue elasticity following release from adjacent tissues . In one study of 216 canine tumour specimens, the total overall shrinkage was 15.6% with 13.7% shrinkage occurring immediately after surgical resection and only 1.7% after formalin fixation .…”

“…In one study of 19 resected canine cutaneous MCTs, the overall specimen shrinkage was 17.7% with 24.4% shrinkage in the grossly normal adjacent skin and only 4.5% shrinkage in the tumour . Other studies have also found a significant effect of both histologic processing and biologic factors, such as tumour infiltration into the grossly normal surgical margin, on shrinkage of specimens . Regardless, specimen shrinkage will result in HTFMs being less than the true tumour‐free margins obtained during surgery.…”

“…The majority of this specimen shrinkage occurs immediately after surgical resection because of the effects of myofibril contractility and tissue elasticity following release from adjacent tissues. [61][62][63][64] In one study of 216 canine tumour specimens, the total overall shrinkage was 15.6% with 13.7% shrinkage occurring immediately after surgical resection and only 1.7% after formalin fixation. 61 Similarly, in cats with VASs, 65 the overall HTFM width was decreased by 33% between surgical resection and histologic examination of the specimen, with 29% of this shrinkage occurring immediately after surgical resection.…”

“…63 Other studies have also found a significant effect of both histologic processing and biologic factors, such as tumour infiltration into the grossly normal surgical margin, on shrinkage of specimens. 64 Regardless, specimen shrinkage will result in HTFMs being less than the true tumour-free margins obtained during surgery. In one study of 51 cutaneous and subcutaneous MCTs resected with curative-intent from 46 dogs, 38 the mean histologic margins were 58% to 65% smaller than the surgical resection margins, representing a 35% to 42% decrease in margin width.…”

Incomplete histological margins following planned narrow excision of canine appendicular soft tissue sarcomas and mast cell tumors, using the residual tumor classification scheme

“…Histologic safety margins have not been defined in veterinary oncology and are infrequently described in human oncology 24 . There is also inherent imprecision within a quantified surgical margin, as the measured margin reduces at each stage of processing following surgery (in vivo, ex vivo, postfixation, subgross, when mounted on glass) before a final assessment of the histologically tumor‐free margin, 32 with a mean length reduction ranging from 35% to 42% 33 . The greater interobserver percentage agreement in histological reporting when the R scheme was used compared to the ≤1 mm scheme (83% vs 68%), demonstrates the benefit of an objective method of histological margin reporting and merits further investigation in prospective studies.…”