Page 439 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

CHAPTER 22 Soft Tissue Sarcomas 417

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Proportion of dogs free of tumor recurrence 0.6
VetBooks.ir 0.8

0.4

0.2

0
0 500 1000 1500 2000 2500 3000
Recurrence-free interval (days)
Lack of tumor cells at surgical margins
Evidence of tumor cells at surgical margins
• Fig. 22.12 Kaplan–Meier curve for disease-free interval in 39 dogs with complete surgical removal of soft
tissue sarcomas and 36 dogs with incomplete surgical margins. (Reprinted with permission from Kuntz
CA, Dernell WS, Powers BE, et al: Prognostic factors for surgical treatment of soft-tissue sarcomas in
dogs: 75 cases (1986–1996), J Am Vet Med Assoc 211:1147, 1997.)

Local tumor characteristics also influence local tumor control. poorer STs. 32,113,126–130 Local tumor recurrence is still possible
Tumor size has been reported to have a negative effect on local after either complete resection or incomplete resection com-
tumor control, especially for incompletely excised STSs. 35,46,111 bined with adjunctive RT. 35,135–138 Consequently, examination of
Local tumor recurrence is up to 7.0 times more likely after mar- the treatment site is recommended at regular intervals, such as
ginal resection of PWTs greater than 5 cm diameter and the risk monthly for the first 3 months, then every 3 months for the first
of local tumor recurrence increases by up to 1.3 times for every 1 12 months, and then every 6 months thereafter. 10,110 The median
cm increase in tumor size. 46,111 This may be because a large tumor time to local tumor recurrence varies from 368 to greater than 798
size influences the ability to achieve complete histologic excision days, which emphasizes the need for long-term follow-up in these
or because a larger tumor size may indicate a more aggressive bio- cases. 32,34,35,46,113,135–137,140,141
logic behavior. 46,116 Tumor size has not been identified as a prog-
nostic factor in other studies, 32,33,139,169 and does not influence Metastasis
local tumor control in dogs treated with surgery and adjuvant RT
or RT alone. 142,169,170 Dogs with fixed or invasive STSs have sig- The overall metastatic rate in dogs with STS varies from 0% to
nificantly decreased DFIs and STs. Invasive or fixed tumors are 31%, with a median time to metastasis of 230 to 365 days. 31–
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associated with a two-fold increased risk for local recurrence com- 34,35,46,113,135–138,141 Factors that increase the risk of metastatic
pared with well-circumscribed STSs after marginal resection, disease include histologic grade, number of mitotic figures, per-
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and PWTs invasive into muscle were eight times more likely to centage of tumor necrosis, and local tumor recurrence. The meta-
recur after marginal resection. 32,111 static rates for dogs with grade I, II, and III STSs are 0% to 13%,
Local tumor recurrence has been associated with an increased 7% to 27%, and 22% to 44%, respectively. 31,35,156 Metastasis is
risk of tumor-related death and decreased STs in some studies. 31,34 significantly more likely in dogs with pleomorphic and undiffer-
In one study of 350 dogs with STSs managed in nonreferral prac- entiated sarcomas compared with FSAs, PNSTs, myxosarcomas,
tices, local tumor recurrence was associated with a 5-fold risk of and liposarcomas. Metastasis is five times more likely when
31
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death. Although many dogs can live with recurrent STSs, local tumors have a mitotic rate of 20 or more mitotic figures/10 HPF
recurrence is more difficult to manage and may result in owners compared with fewer than 20 mitotic figures/10 HPF. In one
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electing euthanasia rather than pursuing further treatment. The study, no dog with a STS at or below the level of the elbow or stifle
median postrecurrence ST for dogs euthanized because of their developed metastatic disease.
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local tumor recurrence is 256 days and this is significantly worse
than the 945 days median postrecurrence ST for dogs with local Survival
recurrence that die of unrelated reasons. This underscores the
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importance of wide excision of STSs initially, as the manage- The MST for dogs with STS ranges from 1013 to 1796 days
ment of recurrent STSs is usually more difficult with curative- after surgery alone to 2270 days with surgery and adjunctive RT
intent treatment of recurrent STSs requiring a more aggressive for nonoral STSs. 25,34,35,135,136 However, the majority of studies
approach, resulting in increased treatment-related morbidity report MSTs that cannot be calculated because only 9% to 33%
with the potential for shorter DFIs, higher metastatic rates, and of dogs eventually die of tumor-related causes after curative-intent