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VETcpd - Surgery
formalin penetration while preserving anatomical architecture. Margins are inked to allow the pathologist to determine if there are tumour cells at cut edges. Inks can be of a single colour or several colours if individual margins need to be recognised (Figure 9).
In addition, the tissue margins are assessed for completeness of excision. Usually
a complete excision or ‘clean margin’
is defined as tumour cells present at
least 3mm from the cut edge. Marginal excision is the presence of tumour
cells within 3mm of any margin, and incomplete excision or ‘dirty margin’
is defined as tumour cells present at
any surgical margin. Complete surgical excision is prognostic for recurrence
and tumour-free survival time (Kuntz
et al. 1997; McSporran 2009). Further surgical excision with 3-cm margins,
or adjunctive therapy if further surgical excision cannot be performed due to lack of available tissue, should be considered
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in animals where incomplete or marginal
excision has been obtained (Bacon et al.
2007).This is most commonly performed
Figure 8A-B: A wound has been partially closed after soft tissue sarcoma resection. Two weeks later the open part of the wound has filled with granulation tissue and the wound is getting smaller by contraction.
by the author in dogs where soft tissue
sarcomas of any grade have previously
been removed by entering the tumour
and removing it piecemeal,‘shelling-out’ the radiation oncologist agrees with the
a tumour where no attempt was made to excise outside the tumour pseudocapsule, or where a tumour was removed with
an unplanned narrow margin or as an excisional biopsy.
Adjunctive Therapies
Radiation therapy
Radiation therapy is best used in conjunction with surgery, rather than
as an alternative. It has made a huge impact on managing soft tissue sarcomas in people, reducing the need for large resections, and in particular allowing marginal resection of tumours of the limbs in order to avoid amputation. Similar findings are seen in dogs.While radiation therapy can be given after unexpected dirty surgical margins, for example where a tumour was removed without cytology, or where a tumour was ‘shelled-out’ instead of being resected with a margin, it is best to avoid these unplanned scenarios, as cure can often be achieved with well-planned surgery. Radiation therapy is best used after planned marginal excision where anatomical factors precluded wide excision, typically in the distal extremities. Discussion with a radiation oncologist should precede surgery, to ensure that
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Only
treatment plan. Surgery is performed
knowing that ‘dirty’ margins will probably
be found on histopathology, and radiation
therapy is used to sterilize the remaining
tumour cells. If radiation therapy is
considered part of the treatment plan, it
is usually given even if ‘dirty’ margins are
not encountered, as histopathology can have false negative results, i.e. failure to recognize residual tumour cells in margins. If radiation therapy is planned, it must wait until the surgical wound has healed or any open skin defect has healed.
Figure 9: The deep surface of a resected soft tissue sarcoma. The lateral and deep edges have been inked in different colours. The deep surface is incised after the ink has dried to allow penetration of formalin.
Recurrence of soft tissue sarcomas
tends to occur 1-3 years after surgery (median one year) but may occur up
to five years later (Kuntz et al. 1997; Bacon et al. 2007; Scarpa et al. 2012). Papers reporting recurrence rates should therefore have follow up of at least one year to give meaningful results. Owners should therefore be advised to monitor the surgical site frequently and should have a veterinary examination every three months. Metastasis occurs in up to 41% of dogs (Bostock and Dye 1980; Kuntz et al. 1997; Heller et al. 2005; Stefanello et al.
Chemotherapy
To date there is not substantive evidence to support the role of systemic chemotherapy for the treatment of soft tissue sarcomas, although metronomic chemotherapy (low-dose continuous chemotherapy) using cyclophosphamide has been shown to delay tumour recurrence in dogs with incompletely resected soft tissue sarcomas (Elmsie et al. 2008).
Outcomes
In both people and dogs, there will be recurrence of some soft tissue sarcomas, regardless of the extent of surgical resection. Conversely there will be some that don’t recur despite only marginal resection.