Page 1424 - Clinical Small Animal Internal Medicine

1362 Section 11 Oncologic Disease

Attempts have been made to link histologically deter- fascial plane deep to the tumor. Prior to pathology sub-
VetBooks.ir mined cellular proliferation markers to MCT prognosis mission, it is recommended to mark margins with either
suture or ink. Histopathology reports should comment
and clinical behavior. Proliferating cell nuclear antigen
(PCNA), argyrophilic nucleolar organizing region‐
Many tumors are large or in too difficult of a location for
associated proteins (AgNORs), and the proliferation on the surgical margins.
protein Ki‐67 have all been evaluated with mixed a reasonable expectation of complete removal. A short
results. Mitotic index has been repeatedly shown to trial (10–14 days) of antiinflammatory prednisone
have the most prognostic value and is required as part (1 mg/kg/day) can often result in significant tumor reduc-
of the initial histopathology report. Tumors with a tion. A recent study found that 70% of all MCTs treated
mitotic index of >5/10 hpf should be treated prognosti- with presurgical prednisone responded to therapy. The
cally as high‐grade MCTs. median reduction in tumor diameter was 45% with a
Evaluation of c‐kit mutation has prognostic utility but median total tumor volume reduction of 80%. Tyrosine
only when closely linked to histopathologic grade. More kinase inhibitors are also used to reduce tumor volume for
importantly, the presence of c‐kit overexpression or muta- surgery in situations where prednisone does not result in a
tion indicates a tumor that is more likely to be responsive significant response. When surgically amendable, these
to the new tyrosine kinase inhibitor class of drugs. medications are not selected as the primary treatment
due to their possible toxicities and cost (Figure 155.4).
For low‐grade (both Kiupel grade I and the majority of
Therapy
Patnaik grade II) MCTs with no evidence of metastasis,
The systemic toxicity of a MCT often requires treatment. complete surgical removal is considered curative and no
Histamine is the compound found in mast cell granules adjuvant therapy is indicated.
that results in the most significant clinical changes. Often, clinicians must determine treatment plans
Activation of histamine receptors (H1 and H2) can lead based on narrow tumor‐free margins of 1–5 mm. Tissue
to toxicity. Severe anaphylactic reactions are a result of specimens will constrict during processing. Adjuvant
systemic H1 receptor activation and can be treated with treatment is indicated if surgery is incomplete and tumor
diphenhydramine and corticosteroids. In times of crisis, cells extend to the surgical margins. There are no clear
intravenous use of steroids is recommended. As a vaso- guidelines for “narrow” surgical margins (1–5 mm) and
active molecule, histamine may also lead to marked each case should be evaluated uniquely. The author is
hypotension which could require both colloidal and usually more aggressive in adjuvant treatment recom-
crystalloid support. H2 is more responsible for stimula- mendations for tumors with ≤1 mm clean margins as
tion of gastric acid. Excessive H2 activation can lead to they have a higher potential to reoccur.
gastric ulceration and clinical side‐effects that include Numerous studies have suggested that there is a subset
anorexia, nausea, hematemesis, and melena. Routine H2 population (20–70%) of cutaneous MCTs that do not
receptor antagonists such as famotidine and ranitidine reoccur when tumor cells extend to the surgical margins.
can be effective but proton pump inhibitors (omepra- Theories include the lack of tumor volume resulting in a
zole) appear to be more potent at reducing gastric acid decrease in progrowth cancer signaling. The small tumor
production and aiding healing of ulcers. volume may also be amenable to self immune defense.
Currently, the author only recommends oral preven- Additionally, there is some belief that the peripheral
tive diphenhydramine and famotidine (at routine dosing) mast cells in a tumor are normal mast cells that respond
for patients with documented MCT metastasis or tumor to chemotactic factors released by the tumor. When the
volumes greater than 5 cm in diameter. tumor is removed and the signals are interrupted, the
Various components within mast cell granules are also normal mast cells vacate the area.
responsible for delays in wound healing. This phenome- Currently, there is no way to determine which low‐
non is most commonly appreciated during incisional grade MCT will reoccur. Thus, all incomplete excisions
biopsy techniques. Wound failure is often noted within should be treated the same. An additional surgery is the
the first 3–5 days postoperatively. ideal treatment and should be considered if there is
Heparin is also released from mast cell granules. adequate local skin for wound closure. For incompletely
Coagulopathies are rare with MCTs as evidence suggests removed low‐grade tumors that cannot be excised,
there is less heparin in malignant MCTs than in normal radiation offers a 90% curative outcome. Radiation
mast cells. Clinically, increased bleeding at the surgical protocols usually entail a total of 45–55 Gy dispersed
site of a MCT is the most common coagulopathy noted. evenly over 18–22 total fractions or treatments.
Surgical removal of all MCTs is considered standard of Although not evaluated in this adjuvant setting, hypof-
care. Surgical removal of the lesion should include at ractionated radiation may also offer added benefit over
least 2 cm of healthy tissue lateral to the lesion and one monitoring alone.