Page 435 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

CHAPTER 22 Soft Tissue Sarcomas 413

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A B
• Fig. 22.9 (A) Wide and marginal resection of soft tissue sarcomas should include an uninvolved fascial
layer for deep margins or, (B) if a defined anatomic fascia layer is not present, then either partial or full
thickness muscle.

for dogs with grade I and possibly grade II STSs with favor- the preponderance of current data, perhaps weakening the gen-
able local characteristics, such as well-circumscribed tumors, less eralizability of this study. Metronomic chemotherapy has been
than 5 cm in diameter, and located on either the thoracic or much less thoroughly studied than wide excision or postopera-
pelvic limb at or below the elbow or stifle. 25,34,46,110,111,117,118 tive RT, and should not be considered an equivalent substitute for
Active surveillance may be appropriate in these cases because, these other modalities at this time. Additional studies are needed
as discussed earlier, local recurrence rates are relatively low (7% to confirm the efficacy of metronomic chemotherapy in the man-
and 34% for incompletely excised grade I and II STSs, respec- agement of dogs with incompletely excised STSs.
tively) 118 and further aggressive treatment may be unnecessary Electrochemotherapy has also been investigated in the man-
in up to 93% of dogs (with incompletely grade I STSs), with an agement of incompletely excised high-grade STSs in 22 dogs. 132
associated increased risk in morbidity and costs. Bleomycin was injected into the tumor bed followed by sequential
Staging surgery is a decision-making surgery. The surgical scar application of trains of biphasic electrical pulses. The local recur-
is excised with minimal margins (<1 cm), with the aim being to rence rate was 36% with a mean time to recurrence of 730 days. 132
determine whether there is histologic evidence of residual tumor Wound dehiscence was reported in 14% of dogs.
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cells. In one study in which the surgical scar was excised with
0.5- to 3.5-cm lateral margins, histologic evidence of residual Surgery and Radiation Therapy
tumor was identified in only 22% of 39 dogs with incompletely
excised STSs. If there is no evidence of tumor cells, then no RT is often recommended in the management of dogs with STSs,
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further treatment is required and these dogs should be monitored particularly after incomplete histologic excision, and adjuvant RT
regularly for local tumor recurrence. If there is evidence of resid- has a documented role in improving local tumor control in people
ual tumor cells, then wide resection of the surgical scar should with STSs. 103,114,128,129 The evidence is less robust in veterinary
be performed with the same margins recommended for primary medicine because all published studies of adjuvant RT in the man-
STSs (2–3 cm lateral to the tumor and one fascial layer deep to agement of dogs with incompletely excised STSs are retrospective
the tumor 10,13,103,110,113,114 ) or the entire surgical scar should be and, more importantly, lack a control group. Local recurrence
irradiated. 128,129 Surgery is preferred to RT for the management rates are similar in studies of dogs treated with marginal resection
of incompletely resected STSs in humans because local tumor alone, compared with recurrence rates occurring in dogs with either
control is better with repeat surgical resection than adjunctive RT marginal resection or incomplete histologic excision treated with
alone. 128,129 adjuvant RT (fractionated or hypofractionated) or intralesional che-
Metronomic (or low-dose) chemotherapy is another option motherapy (Table 22.3); however, it is important to recognize that
for the management of dogs with incompletely excised STSs. The study results cannot be compared because of differences in study
administration of piroxicam and low-dose cyclophosphamide in populations and methodologies. Furthermore, because canine STSs
30 dogs with incompletely excised STSs resulted in a significantly have a biologic behavior similar to that of low-grade STSs in peo-
prolonged disease-free interval (DFI) compared with a nonran- ple and because RT significantly improves local tumor control in
domized control group of 55 dogs with incompletely excised people with incompletely excised STSs, RT should still be consid-
STSs and no metronomic chemotherapy. 131 Of note, the control ered in the management of dogs with STSs. 114,128,129 RT can be
population used in this study experienced recurrence rates much used as an adjunct to surgery after either planned marginal resec-
greater than what is expected in the general population based on tion or unplanned incomplete histologic excision. Marginal surgical