Histologic Grade Predicts Recurrence for Marginally Excised Canine Subcutaneous Soft Tissue Sarcomas

Abstract

Local recurrence of marginally excised subcutaneous soft tissue sarcomas is variable and difficult to predict. This study aimed to identify predictors of local recurrence after excisional biopsy. Medical records of 236 dogs from which tumors had been received between 2004 and 2007 were analyzed. Medium- to large-breed dogs, median age 10 years, were most commonly affected. A total of 139 tumors were graded histologically: 71 were grade 1 (51%); 59, grade 2 (42%); and 9, grade 3 (7%). Of these, 34 tumors (25%) were completely excised, and 104 (75%) were marginally excised. None of 30 completely excised tumors with follow-up information recurred. Three of 41 grade 1 tumors (7%), 14 of 41 grade 2 tumors (34%), and 3 out of 4 grade 3 tumors recurred after marginal excision. Kaplan-Meier survival curves were generated to evaluate survival and the tumor-free interval. The log-rank test and log-rank test for trend were used for comparisons. Tumor recurrence-free intervals for dogs with grade 1 and 2 tumors and for those with grade 1 and 3 tumors differed significantly (P = .0027 and .0001, respectively) and overall were inversely related to tumor grade (P = .0007). Kaplan-Meier survival curves, regardless of recurrence, for patients with grade 1, 2, or 3 tumors treated by marginal excision did not differ significantly, and none differed from the survival curves of patients treated by complete excision. In conclusion, histologic grade is a strong predictor for recurrence of marginally excised subcutaneous soft tissue sarcomas. Clean margins predict nonrecurrence. Tumor recurrence did not significantly reduce survival time.

Prognostic Factors for Cutaneous and Subcutaneous Soft Tissue Sarcomas in Dogs

“…These neoplasms-including histiocytic sarcoma, lymphangiosarcoma, hemangiosarcoma, synovial cell sarcoma, leiomyosarcoma, rhabdomyosarcoma, fibrosarcomas involving the oral cavity, and brachial plexus peripheral nerve sheath tumors (PNSTs; also termed schwannomas, neurofibromas, 12 or nerve sheath tumors 16 )-are specifically excluded from STS grouping because they can be consistently distinguished by microscopic features and/or anatomical location and because as a group, they exhibit more malignant biological behavior. 8,11,17,19,32,33,35,40,50 Thus, when applied to canine tumors of the skin and subcutis, the term soft tissue sarcoma is a grouping of tumors that is becoming a diagnosis of exclusion. This is in contrast to the grouping scheme for human STSs, which is not exclusionary.…”

“…48 Another common drawback of STS prognostication studies is a lack of multivariable analysis. 4,5,7,11,20,25,37,40,46,49,50 In these studies, numerous prognostic variables were explored independently without adjusting for the effects of other prognostic variables. There is some disparity in the way in which canine STSs are grouped among studies.…”

“…Incomplete (''dirty'') margins are usually defined as having neoplastic cells at surgical margins; however, some studies include tumors having neoplastic cells within 1 mm of surgical margins. 48 Close (also referred to as ''marginal'' or ''narrow'') margins have been variably defined as neoplastic cells within 1 mm of surgical margins or as absence of tissue outside the pseudocapsule; 40 neoplastic cells 1 to 3 mm from the surgical margin; 50 neoplastic cells within < 5 mm of the surgical margin; 6 and neoplastic cells within < 10 mm of the surgical margin. 48 Complete margins have been variably defined as tumor pseudocapsule !…”

“…48 Complete margins have been variably defined as tumor pseudocapsule ! 1 mm from the surgical margin; 40 neoplastic cells > 3 mm from the surgical margin; 3,50 neoplastic cells > 5 mm from the surgical margin; 6 and neoplastic cells > 10 mm from the surgical margin (wide). 48 Some studies provide little detail as to how completeness of surgical margins was categorized.…”

“…STSs with complete margins are less likely to recur, 32 and they have significantly longer tumor-free intervals than those without. 11,40 Trends described for recurrence rates of STS with incomplete and close margins are similar (reports ranging from 2 of 12 [17%] to 10 of 36 [28%]); 32,40,50 however, differences in recurrence rates have not been statistically measured. Recurrence rates for STS with tumor pseudocapsule > 1 mm from the surgical margin are as low as 0 of 30 (0%), regardless of grade.…”