Page 434 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

412 PART IV Specific Malignancies in the Small Animal Patient

STSs. In two studies of dogs with PWTs, the local recurrence
25
rate was 18% to 20.0% despite 60% to 63% of these tumors
being incompletely excised.
The only prognostic factor
46,111
VetBooks.ir for local recurrence in both studies was tumor size, with local
recurrence up to 7.0 times more likely for PWTs greater than 5
cm diameter with the risk of local tumor recurrence increasing
by up to 1.3 times for every 1 cm increase in tumor size. 46,111
In a study of 350 canine STSs treated surgically in nonrefer-
ral practices, the local recurrence rate was 21% despite only
34
5% of these STSs being excised with wide surgical margins.
Histologic grade was the only prognostic factor for local tumor
recurrence in this study, with grade III STSs having a 5.8-fold
increased risk for local recurrence compared with grade I and
II STSs. Taken in totality, these studies suggest that accept-
34
able local tumor control rates are achievable with less aggressive
A surgical approaches; however, they also illustrate that the tradi-
tional consideration of STSs having a similar biologic behavior
is overly simplistic. The ideal treatment for dogs with cutane-
ous and subcutaneous STSs should not necessarily be standard-
ized but rather tailored to each individual case according to
location, tumor size, degree of infiltration, histologic subtype,
histologic grade, and completeness of excision. If insufficient
information is available before surgery to individualize treat-
ment options, then wide surgical resection (with 2–3 cm lateral
margins and one fascial layer for deep margins) is the preferred
surgical approach.
The resected tumor should be pinned out to the original
dimensions to prevent shrinkage during formalin fixation 119 ; the
lateral and deep margins should be inked to aid in histologic iden-
tification of surgical margins; and any areas of concern should be
tagged with suture material, inked in a different color, or submit-
ted separately for specific histologic assessment. Histologic mar-
B gins and histologic grade are important in determining the need
and type of further treatment.
There are a number of limitations with our current ability to
assess the adequacy of the completeness of the excision and risk of
local tumor recurrence, and thus our ability to determine which
patients require further therapy and which patients may benefit
from monitoring. These include sample shrinkage after excision
and during formalin fixation, the techniques used to assess margins
histologically, the lack of information on the definition of a “nar-
row” histologic margin, and the significance of narrow margins on
the risk of local tumor recurrence. 13,120 Perhaps most important is
that histopathology is an examination of excised tissue ex vivo and
not residual tissue in vivo, and that this assessment is made days
after surgery rather than in real time. A number of advancements
are being made in both veterinary and human surgical oncology in
the real-time assessment of the wound bed after excision of STSs
for residual neoplastic disease. 121–125 Hopefully, as these real-time
C
in vivo assessment methods are validated and become available for
• Fig. 22.8 Wide resection of a grade II soft tissue sarcoma from the cra- clinical use, there will be an improvement in the rate of complete
niolateral thigh of a dog. (A) Planned lateral surgical margins are indicated histologic excision and local tumor control.
with a sterile marker pen 3 cm in all directions around the soft tissue sar- The treatment options for incompletely excised STSs include
coma. (B) An incision is then performed along the marked margins, and active surveillance (i.e., frequent observation for local tumor
continued deeply to include an uninvolved fascial layer. (C) Primary closure recurrence and appropriate treatment if the tumor recurs),
after wide resection of the soft tissue sarcoma. staging surgery, wide excision (i.e., revision surgery), RT, met-
ronomic chemotherapy, and electrochemotherapy. The first
STSs and liposarcomas, fewer than 10% were excised with 3 surgery provides the best opportunity for local tumor control,
cm lateral margins, and local tumor recurrence was reported as the management of incompletely resected tumors increases
in 28% of dogs (29% of marginal excisions, 17% of narrow patient morbidity and treatment costs, increases the risk of
excisions, and 5% of wide excisions); local tumor recurrence further local tumor recurrence, and potentially decreases
was significantly more likely to occur with fixed and invasive ST. 10,31,34,35,105,110,126–130 Active surveillance may be appropriate