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An Urban Experience
capsule. This is also used if the capsule is accidentally entered during dissection as the surgical field is now contaminated. Gross and/or microscopic disease remains.
• A marginal margin is achieved by an extracapsular dissection through the reactive zone around the mass. Classically these are termed ‘shell-outs’ and involve peeling the mass out from its tissue bed and off local attachments. Both benign and malignant lesions
may have extracapsular microextensions of disease, microsatellites (in the reactive zone, e.g. mast cell disease), and ‘skip’ metastases of high-grade lesions (in normal tissue of the same compartment e.g. soft tissue sarcomas). These both have implications for marginal excisions in terms of potential for local recurrence.
• A wide margin is achieved by en bloc removal of the lesion, its capsule and the surrounding reactive zone but always working in normal uncontaminated tissue within the compartment of the lesion. Non-neoplastic, non- reactive intracompartmental normal tissue is left at the margins and there is the possibility of ‘skip’ metastases arising in the remaining portion of the compartment.
• A radical margin removes the lesion, reactive zone,
and all the tissue of the associated compartment. There is no potential for residual neoplasm locally. The typical example is amputation, along with variants such as hemi- pelvectomy.
Treatment options broadly exist as;
1. Curative-intent excision with reconstruction, plus radiation if incomplete margins
2. Pre-operative radiation (48Gy) with sterilisation of tissue around tumour and planned marginal excision of mass
3. Planned marginal excision of mass then post-operative radiation (57Gy) to sterilise tumour bed
Treatment, including surgery and radiation therapy, has focused on reducing local recurrence and increasing survival time associated with ISS. Reported rates
of local recurrence post-treatment range from 26-
59%. Recurrence rates and survival times have been documented following various combinations of surgery (marginal vs. wide local vs. radical), radiation therapy (pre- or post-operative) and chemotherapy, with no reliable difference in outcome noted between various aggressive treatment protocols. In two studies, completeness of surgical excision was shown to affect rate of local recurrence, reporting 58-69% recurrence rates with incomplete versus 19-22% with complete excision. In addition, complete excision has been associated with a longer time to first recurrence and tumor free interval (time to first recurrence or metastasis).
Historically, an excision of ISS in cats with 2-3 cm margins and one fascial plane deep to the tumour bed has been adopted (from canine sarcomas), but it may not be adequate when using surgery alone considering the high historical rates of local recurrence. In response to this, several authors have suggested more radical methods, including surgical margins of greater than 3 cm and 1 to 2 fascial planes deep to the tumor, along with partial scapulectomy, osteotomy of spinous processes or hemipelvectomy when indicated. Currently, the Vaccine- Associated Sarcoma Task Force recommends multi- modal treatment, including surgical resection with at least 2 cm margins in all planes, although the use of 3 to 5 cm margins is considered. A study on feline vaccine- associated sarcomas in cats following excision with 3cm wide margins and one facial plane deep showed that 1cm away from palpable tumor, the tissue was free of neoplasia in 13% cases, by 2cm from the mass, 32% were free of cancer cells, and by 3cm, 94% were free of neoplasia. The single fascial plane achieved a tumor-free deep margin in 94% cases.
Palpation may suggest a discrete mass, but post- contrast CT often shows the true extent of infiltrative disease, which cannot be appreciated by feel
alone. Radical first excision of ISS yielded significantly longer median time to first recurrence (325 days) than did marginal first excision (79 days). Median survival time is significantly longer in cats with tumours <2cm in diameter compared to those with tumours 2cm in diameter.
Work recently completed (to be presented) in 91 cats with ISS treated by an excision of 5cm and 2 fascial planes (without radiation therapy or chemotherapy), shows the rate of recurrence to be 14% with rate of metastasis of 20%. Median survival time of cats with recurrence was 499 days and without recurrence was 1461 days. Median survival time of cats with metastasis was 388 days and without metastasis was 1528 days. Survival was significantly affected by both recurrence and metastasis. Major complications occurred in 11 cats; 7 had incisional dehiscence.

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