Page 412 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

390 PART IV Specific Malignancies in the Small Animal Patient

Some authors advocate prophylactic irradiation of cyto-
logically negative regional LNs (prophylactic nodal irradiation
Owing to the generally low risk of postsurgi-
[PNI]).
114,123,124,163
VetBooks.ir cal metastasis in low- to intermediate-grade tumors, PNI is prob-
ably unwarranted in this group of patients, and at least one study
has demonstrated no advantage in terms of disease-free or overall
survival when PNI is employed 159 ; however, in MCTs at high risk
for metastasis, PNI may provide improvement in outcome over
local site irradiation only. 114,163
For cases in which planned curative excisional surgery is unsuc-
cessful and histologic margins are incomplete, further local ther-
apy is generally warranted. If possible, a second excision of the
surgical scar with additional wide margins should be performed
(Fig. 21.6); however, some evidence suggests that marginal, “stag-
ing” reexcision of dirty surgical scars may be associated with an
acceptable likelihood of achieving tumor-free margins. 78,162,164
Alternatively, adjuvant RT can be used in cases in which reexcision
is not an option. Not all MCTs with surgically incomplete mar-
gins will recur; in some studies only 10% to 30% of MCTs with
histologically confirmed incomplete margins did so. 92,162,165 One
study suggests that measurement of proliferation indices (Ki67 and
PCNA) via IHC may be useful in predicting likelihood of recur-
92
rence after incomplete resection of intermediate-grade MCTs.
Although recurrence rates vary by study, several studies have dem-
onstrated increased local recurrence rates and/or decreased overall
STs in dogs with incompletely resected MCTs. 28,78,80,120 Fig. 21.7
summarizes the treatment recommendations for clinical stage 0
and I, histologically low- or intermediate-grade MCTs.
Alternative local therapies for MCTs have been reported and
include hyperthermia in combination with RT, 166 intralesional
brachytherapy, 167 photodynamic therapy, 168,169 intralesional cor-
• Fig. 21.6 Reexcision of a mast cell tumor from the skin of a golden ticosteroids, 170,171 cryotherapy, and electrochemotherapy. 172–175
retriever. The first surgery resulted in incomplete surgical margins. Three- Although some have advocated the use of intralesional deionized
cm margins are taken around and deep to the previous incision and the water at the site of an incompletely excised MCT, clinical data
entire sample is again submitted for margin analysis by the pathologist. indicate that this approach is not effective at preventing local

Anatomic site amenable to wide surgical excision?

Options:
Ideal: Cytoreductive surgery and adjuvant radiation therapy
No
Alternative choices:
Yes Cytoreduction followed by medical therapy
Cytoreduction followed by active surveillance
Radiation therapy alone (possible surgery to follow)
Medical therapy alone (possible surgery to follow)

Excise with wide surgical margins.
Assess margins and confirm grade.

Options:
No Reexcision with wide margins
“Staging” reexcision
Complete surgical margins? Adjuvant rediation therapy
Adjuvant medical therapy
Active surveillance
Yes

Routine follow-up:

1, 3, 6, 9, 12, 15, 18 months
q 6 months thereafter
Physical exam and lymph node exam
• Fig. 21.7 Suggested treatment approach for clinical stage 0 and 1 canine mast cell tumors of low or
intermediate grade.