Page 106 - WSAVA2018
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 25-28 September, 2018 | Singapore
been performed. For suspected FISS, referral should always be recommended, as radical excision is typically required and outcomes are improved if the first surgery is aggressive. Incisional biopsy should be considered to confirm the diagnosis, but excisional biopsy is NOT recommended for FISS.
The important features on histopathology report for canine STS (apart from diagnosis of STS) are:
1. Grade: A 3 tier scheme is typically used, based on degree of differentiation, necrosis and mitotic rate. However, the exact methodology for how these factors are assigned is not standardised and so may vary between pathologists. Grade appears to impact risk of metastasis and local recurrence, though confirming suspected metastasis or recurrence is inconsistently done in the published literature. Based on available studies, the metastatic potential is low (< 15-20%) for grade 1 and 2 STS, and up to 40-50% for grade 3 STS. Histologic grade is variably prognostic for survival in the published literature (1)
2. Mitotic index: What is typically reported in the veterinary literature as mitotic index should be more correctly referred to as mitotic count. However, for consistency, we will continue to use the term mitotic index (MI). MI is predictive for survival with < 9/10 high power fields generally being best and > 20 being worse.
3. Margins: Standardised reporting of margins as ‘complete/clean’ versus ‘narrow/close’ is also lacking. Generally, any complete margin is likely sufficient for grade 1 or 2 STS - though recurrence can occur, it is very rare. Recurrence even with complete histologic margins is somewhat more common in grade 3 STS. As for mast cell tumours, the deep margin is qualitative as well as quantitative - even if narrow, if the deep margin includes fascia or muscle then this should
be an effective barrier to tumour cell invasion. With narrow histologic margins (defined as < 1mm or within the tumour pseudocapsule), < 10% of grade 1 tumours, approximately 1⁄3 of grade 2 tumours, and 3⁄4 of grade 3 tumours recurrred in one study (2), and it appears likely that recurrence rates are similar for incomplete versus close margins. However, neither margin status nor tumour recurrence have shown a definitive impact on survival time.
Within those tumours typically classified as STS, the exact histologic subtype does not seem to significantly affect prognosis, though there is some association between subtype and grade or mitotic rate. At this stage, without evidence to suggest differences in behaviour, extensive investigation to assign a specific subtype is not generally recommended once a diagnosis of STS has been confirmed.
For FISS, completeness of margins is important, with incomplete margins associated with recurrence
(approximately 10x more frequently than complete margins) and with disease free interval. Because of the invasive nature of these tumours, incomplete margins are common without radical surgery.
Whilst STSs may appear to be well encapsulated, it
is the cells that are at the pseudocapsule margin that are most active. Surgery that ‘shells out’ the STS is an intralesional excision and is associated with a high local recurrence rate. STSs have microscopic projections at their periphery invading surrounding normal tissues.
Wide surgical excision is the treatment of choice for STSs. The recommended surgical margins for STSs are proportional to grade. For FISS cases, radical margins
of 5cm are recommended. It is important to obtain appropriate deep margins as well as lateral margins. The deep margin is considered a qualitative margin rather than a quantitative margin and should consist of fascia or muscle rather than adipose tissue, which is a poor anatomic barrier to tumour extension.
Low grade STSs on the extremities present a particular situation and have been reported to be able to be managed with more marginal resections. If there is insufficient tissue for primary closure or if tension is an issue, then open wound management is reported to be successful.
Adjunctive therapy
· Local treatment: In cases of incomplete or narrow histological margins (i.e. risk of local recurrence), additional local therapy with revision surgery or radiation therapy is recommended. However, since many incompletely or narrowly excised grade 1 or
2 STS do not recur, if clients do not wish to pursue additional therapy then ongoing monitoring is reasonable. For grade 3 tumours, the risk of local recurrence is much higher and adjunct therapy is more strongly recommended. Local chemotherapy with platinum-impregnated beads or intra-incisional 5-fluorouracil has been reported, but only in small numbers of dogs. Although recurrence rates are low, the majority are grade 1 or 2 STS and so the efficacy of these local therapies is as yet unknown, and there is some risk of toxicity.
· Metronomic chemotherapy with low dose daily oral cyclophosphamide along with daily piroxicam has been shown to significantly improve disease free interval compared to surgery alone in dogs with incompletely excised STS, however all of the tumours in the control group in this study recurred (median disease free interval of approximately 7 months), which is inconsistent with other studies (3).
· Adjuvant chemotherapy with doxorubicin is often recommended following surgery for grade 3 STS due to the risk of metastasis and is effective in improving disease-free survival in humans, however this approach has not been proven to improve survival in canine STS.

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