Characterizing Microscopical Invasion Patterns in Canine Mast Cell Tumours and Soft Tissue Sarcomas

Evaluating the relevance of surgical margins. Part one: The problems with current methodology

The goal of cancer surgery is to achieve a "clean" microscopic resection, with no residual tumour remaining in the wound. To achieve that goal, the surgeon typically incorporates a measured buffer of grossly normal tissue about the entire circumference of the tumour. Microscopic analysis of the resection boundaries is then performed to determine if all traces of the tumour have been completely removed. This analysis is thought to provide a surrogate indication as to the likelihood for that tumour to recur after surgery. However, it is recognised that tumour recurrence may not occur even when microscopic evidence of tumour has been identified at the resection margins, and recurrence can also occur when conventional histology has considered the tumour to have been completely removed. The explanations for this dichotomy are numerous and include technical and practical limitations of the processing methodology, and also several surgeon-related and tumour-related reasons. Ultimately, the inability to confidently determine when a tumour has been removed sufficiently to prevent recurrence can impact on the ability to provide owners with confident treatment advice. In this article, the authors describe the challenges with defining the true extent of the tumour margin from the perspective of the surgeon, the pathologist and the tumour. The authors also provide an analysis of why our current efforts to ensure that all traces of the local tumour have been successfully removed may provide an imperfect assessment of the risk of recurrence.

Marginal excision of cutaneous mast cell tumors in dogs was not associated with a higher rate of complications or prolonged wound healing than marginal excision of soft tissue sarcomas

OBJECTIVE

To compare wound healing following planned marginal excision of cutaneous mast cell tumors (MCTs) with that of soft tissue sarcomas (STSs) and to identify risk factors for wound healing complications and delay in healing.

ANIMALS

126 dogs that underwent intentional marginal excision of cutaneous MCTs (n = 77) or subcutaneous STSs (49).

PROCEDURES

Medical records of included dogs were reviewed and signalment, tumor size, tumor location, skin closure type, time to healing, reported complications, histopathological grade, and surgical margins were recorded. These variables and outcomes (complication rate and time to complete healing) were compared between dogs in the MCT and STS groups. Potential risk factors for complications and delayed healing were analyzed.

RESULTS

No significant difference between the groups was found in any of the variables. Wound healing complication rates were 29% (22/77) for the MCT group and 31% (15/49) for the STS group. The mean ± SD time to complete healing was 16.5 ± 7.5 days for the MCT group and 17.7 ± 9.3 days for the STS group. These outcomes did not differ significantly between groups. For both groups, the use of subdermal plexus flap reconstruction was associated with the development of complications and increased time to complete healing.

CLINICAL RELEVANCE

Marginal excision of cutaneous MCTs was not associated with a higher rate of complication or prolonged wound healing, compared with marginal excision of STSs. The use of flap reconstruction in skin closure may delay healing and planned adjuvant therapy. Owners should be counseled regarding these risks and where appropriate and feasible, surgery without reconstruction should be considered.

Intersurgeon agreement in determining 3 cm surgical margins of subcutaneous tumors in dogs

OBJECTIVE

To evaluate intersurgeon agreement in performing a 3 cm wide surgical excision for subcutaneous malignancies in dogs.

STUDY DESIGN

Prospective, blinded, randomized, clinical study.

ANIMALS

Client-owned dogs with subcutaneous tumors undergoing curative-intent, wide surgical excision between April 2019 to March 2020.

METHODS

Four surgeons, instructed to perform a 3 cm wide excision, each sequentially indicated their proposed skin incision locations around subcutaneous tumors, without knowledge of the other surgeons' proposed incisions. A tripod-mounted camera and laser positioning system were used to photograph each surgeon's proposed margin length. A random-effects model was used to estimate the standard deviation of margin lengths that would be expected from a random sample of surgeons.

RESULTS

Each of the four surgeons provided 33 independent radial measurements from 11 tumors (six soft tissue sarcomas and five mast cell tumors), for a total of 132 radial measurements. No individual surgeon consistently proposed longer or shorter margin incision locations. The prediction interval for a future margin measurement was 6 mm, implying that the 95% confidence interval of an individual surgeon's margin length would be within ±6 mm of the mean margin length from a random sample of surgeons.

CONCLUSION

Ninety-five percent of surgeons would be expected to deliver a surgical dose between 2.4-3.6 cm, for a theoretically uniform surgical dose of 3 cm wide margins.

CLINICAL SIGNIFICANCE

Surgical doses are likely to vary at clinically relevant levels among surgeons, complicating design and interpretation of studies attempting to identify an ideal surgical dose.

Surgical Margins in Canine Cutaneous Soft-Tissue Sarcomas: A Dichotomous Classification System Does Not Accurately Predict the Risk of Local Recurrence

Simple Summary

Histological evaluation of surgical margins is crucial for correct prognostication and adjuvant treatment recommendation after excision of soft tissue sarcoma (STS) in dogs. Incompletely excised STS have a high risk of local recurrence (LR), while completely excised STS without other negative prognostic factors are generally associated with a good prognosis. However, guidelines are lacking on how to manage STS excised with clean but close margins (CbCM), although some authors advocated their inclusion in the tumor-free margin group. This retrospective study investigates the impact of CbCM on LR of canine STS. Ninety-eight surgical excised canine STS at first presentation were included. Cumulative incidence of LR was estimated for each category of margins (tumor-free, infiltrated, CbCM), and after grouping CbCM alternatively in the tumor-free and infiltrated category. Cumulative incidence of LR at three years differed significantly between the three categories, and it was estimated to be 42% with infiltrated margins, 23% with CbCM, 7% with tumor-free margins. Both when CbCM were grouped with infiltrated margins or with tumor-free margins, the incidence of LR was statistically different. The rate of LR with CbCm was greater than with tumor-free margins. The category CbCM may be considered as a separate prognostic category.

Abstract

Adjuvant treatments are recommended in dogs with incompletely excised cutaneous soft-tissue sarcoma (STS) to reduce the risk of local recurrence (LR), although guidelines are lacking on how to manage clean but close margins (CbCM). This retrospective study investigates the impact of CbCM on LR of canine STS. Ninety-eight surgically excised canine STS at first presentation were included. Tissue samples were routinely trimmed and analyzed. Cumulative incidence of LR was estimated for each category of margins (tumor-free, infiltrated, CbCM), and included CbCM in the tumor-free and infiltrated category, respectively. The prognostic impact on LR was then adjusted for relevant prognostic factors. Cumulative incidence of LR at three years differed significantly between the three categories (p = 0.016), and was estimated to be 42% with infiltrated margins, 23% with CbCM, 7% with tumor-free margins. Both when CbCM were grouped with infiltrated margins (p = 0.033; HR = 5.05), and when CbCM were grouped with tumor-free margins (p = 0.011; HR = 3.13), a significant difference between groups was found. STS excised with infiltrated margins had the greatest risk of LR. The rate of LR with CbCm was greater than recurrence rate of tumor-free margins. The category CbCM may be considered as a separate prognostic category.

Evaluation of the neoplastic infiltration of the skin overlying canine subcutaneous soft tissue sarcomas: An explorative study

Studies regarding the neoplastic infiltration of the skin overlying canine subcutaneous soft tissue sarcoma (sSTS) are lacking. In case of the absence of tumor infiltration, there would be the possibility of leaving this unaffected skin in place, thus simplifying surgery. The aim of the study was to investigate whether the skin overlying sSTSs is infiltrated by neoplastic cells. Dogs with sSTSs treated surgically were prospectively enrolled. After excision, the skin was dissected from the tumor along the natural surgical plane of cleavage and histologically evaluated. Twenty-nine dogs with an sSTS were included (22 grade I, 6 grade II, and 1 grade III). The sSTS-overlying skin was not tumor-infiltrated in 14/29 cases (48.3%). A higher frequency of infiltration was observed in higher grade sSTSs (grades II and III, 100%; P = .006); nevertheless, 8/22 grade I sSTSs (36%) also showed cutaneous infiltration. This infiltration involved the dermis of the skin directly in contact with the tumor (multifocal in 11 and diffuse in four cases). Although the cutaneous tumor infiltration is less frequent in grade I sSTSs and a wide excision may still be the safest treatment for any sSTS for a greater possibility of local control, this study opens the possibility to a less aggressive cutaneous excision, but still with a local curative intent, as only the skin directly in contact with the sSTS has been proven to be tumor-infiltrated. Additional studies are warranted to confirm that excision of only this skin may guarantee a complete local control, especially in lower-grade sSTSs.

Evaluation of a modified proportional margin approach for complete surgical excision of canine cutaneous mast cell tumours and its association with clinical outcome

Canine cutaneous mast cell tumours (MCTs) represent a common neoplasm in veterinary practice. Several reported techniques are available to guide surgical excision. Our study examined one hundred cutaneous MCTs that were excised surgically using a modified proportional margin approach. A 2 cm lateral margin upper limit was applied for any tumour diameter that exceeded this size with a deep surgical margin of one fascial plane applied. A retrospective, cross-sectional study with follow-up was used to determine the clinical utility of this excision technique. Associations between explanatory variables of tumour size and grade were compared with outcomes of complete excision and size of histologic tumour-free margins (HTFM) using the appropriate Pearson's χ² and Fisher's exact tests. Follow-up data evaluated tumour recurrence and patient survival. Ninety-five percent of MCTs (95/100) were completely excised. No significant association in the achievement of complete excision between low- and high-grade MCTs (P = .48) was noted. Tumour size was not associated with the rate of complete excision (P = .06). Tumour grade and size did not influence the size of the HTFM (P = .94 and P = .14, respectively). Overall, a recurrence rate of 3% (3/100 tumours) and de novo MCT development rate of 7.7% (5/65 dogs) was noted, with median follow-up period of 593 days (range 180-1460 days). Post-operative metastases were seen in 4.6% of dogs (3/65). Therefore, a modified proportional margin approach with 2 cm lateral margin upper limit is a suitable technique to guide surgical excision of canine cutaneous MCTs.

Long-term outcomes of dogs undergoing surgical resection of mast cell tumors and soft tissue sarcomas: A prospective 2-year-long study

OBJECTIVE

Report clinical outcomes of dogs with surgically excised mast cell tumors (MCT) and soft tissue sarcomas (STS).

STUDY DESIGN

Prospective clinical study.

SAMPLE POPULATION

Fifty-three dogs with 52 MCT (50 low grade, 2 high grade) and 19 STS (12 grade I, 6 grade II, 1 grade III).

METHODS

All dogs were examined at 3, 6, 12, 18, and 24 months postoperatively, with cytologic or histopathologic evaluation of suspected local recurrences. Dogs euthanized because of study tumor-related causes underwent necropsy.

RESULTS

Median intraoperative margins were 20 mm and 30 mm wide for MCT and STS, respectively, with 1 fascial plane resected en bloc. The narrowest histologic tumor-free margins measured <1 mm in 21 of 52 (40%) MCT and 7 of 19 (37%) STS. All dogs were followed for 24 months. Two of 50 (4%) low-grade MCT were diagnosed, with local recurrence 181 and 265 days postoperatively. Two of 36 (6%) dogs with low-grade MCT developed visceral metastasis 181 and 730 days postoperatively. One of 2 dogs with high-grade MCT developed local recurrence 115 days postoperatively. No local recurrence or metastasis was diagnosed after excision of 19 STS.

CONCLUSION

Local recurrence rates among predominantly low- to intermediate-grade MCT and STS were low, despite a high prevalence of histologic tumor-free margins <1 mm. Surgical recommendations for high-grade tumors cannot be extrapolated from this population.

CLINICAL SIGNIFICANCE

Surgeons should seek to achieve microscopically complete excision for MCT and STS while minimizing patient morbidity and considering limitations of histopathology in predicting outcomes.