Page 1267 - Cote clinical veterinary advisor dogs and cats 4th

636 Mast Cell Tumors, Dog

are evaluated with both grading systems, better results than when treatment is MCTs with corticosteroids, chemotherapy, or
immunohistochemistry for KIT and Ki-67, performed with macroscopic (measurable) targeted therapies in an attempt to prevent
VetBooks.ir exon 8 and 11 mutations, and argyrophilic ○ Potential indications for RT for MCTs • For dogs with high-grade or high MI MCTs,
recurrence remains unproved.
disease.
polymerase chain reaction (PCR) for KIT
nucleolar organizer region (AgNOR) special
survival times vary due to metastasis and
include incompletely excised, low-grade
staining. This panel may be useful to guide
not possible; as an adjunct to surgery and
therapy and monitoring are recommended
therapy for dogs with multiple or recurrent MCTs where wider surgical excision is tumor recurrence. Generally, additional
MCTs or tumors with aggressive biologic chemotherapy in dogs with high-grade (staging, chemotherapy, and/or targeted
behavior or “borderline” histopathologic MCT; and to attempt cytoreduction of therapy). Case series of prolonged survival
characteristics. nonresectable MCTs. times in dogs with such tumors treated with
• The goal of chemotherapy is to delay or aggressive local and systemic therapy exist,
TREATMENT prevent metastasis and possibly local recur- and owners should be made aware of all
rence or attempt to cytoreduce or slow treatment options.
Treatment Overview progression of nonresectable tumors or • Importantly, 10%-40% of affected dogs
MCTs have a wide variety of biological metastatic lesions. Potential indications for (especially pugs and boxers) develop addi-
behaviors and outcomes, and treatment can chemotherapy in dogs with MCT include tional cutaneous MCTs in their lifetime.
include surgery, radiation therapy (RT), chemo- ○ Dogs with high-grade MCT or tumors Owners should be advised that any new
therapy, or a combination of these modalities. with MI > 5 skin mass should be addressed right away.
Targeted therapies (i.e., receptor tyrosine kinase ○ Dogs with metastasis at diagnosis or with • Tumors located on mucous membranes may
inhibitors) are now widely available and may recurrent tumors have a worse prognosis compared with MCTs
be indicated for patients with nonresectable ○ Dogs with tumors in locations associated of haired skin.
or recurrent tumors. Consultation with an with aggressive behavior (see above)
oncologist for current treatment options is ○ Before attempting surgical excision PEARLS & CONSIDERATIONS
warranted in these cases. A global overview of of large, fixed tumors or tumors with
treatment is provided on p. 1436. peritumoral edema or bruising Comments
○ Chemotherapy drugs considered to • Rechecks with physical exams at least q 4-6
Acute General Treatment be effective in the treatment of MCT months to detect and treat new MCTs as
• Surgery is the primary treatment modality include CCNU (lomustine), prednisone, soon as possible
for MCTs. vinblastine, vinorelbine, chlorambucil, • Grossly, fine-needle aspirates of MCTs can
○ Preoperative H1 histamine blockers (such cyclophosphamide, hydroxyurea, and look transparent and watery and are indistin-
as diphenhydramine): begin therapy a few others. Special handling requirements guishable from fat. All fine-needle aspiration
days before and premedicate immediately and potentially severe or life-threatening samples must be examined cytologically to
before surgery (and ongoing for nonresect- adverse patient effects exist with these differentiate fat from MCT.
able or metastatic disease) chemotherapeutic drugs. These concerns • Because of the varied biologic behavior of
○ Preoperative corticosteroids to attempt to and rapid evolution of protocols warrant MCT, factors such as tumor grade, MI,
shrink the tumor (measure and record at consultation with/referral to an oncologist. location and size of the tumor, regional
baseline first), making complete surgical • Targeted therapies work by inhibiting cellular and systemic metastasis, and completeness of
resection more viable: prednisone 0.25-0.5 receptors. A receptor tyrosine kinase inhibitor surgical excision are essential for developing
mg/kg PO q 24h × 5-7 days preopera- (RTKI) currently in common use for MCT an appropriate treatment plan and prognosis.
tively, especially if MCT is difficult to in dogs is toceranib phosphate (Palladia) for • Intralesional therapies such as de-ionized
access surgically recurrent or metastatic grade II and III MCT. water or corticosteroids may provide tem-
○ Proton pump inhibitors (omeprazole 0.5-1 This drug has been used in combination porary shrinkage of MCTs but are rarely
mg/kg PO q 24h) and/or H2 histamine with other therapies in many dogs with effective for long-term tumor control and
blockers are indicated for dogs with MCTs, and consultation with an oncologist are not recommended.
measureable MCT (preoperatively or in is warranted for specific current treatment
cases of nonresectable disease) to attempt recommendations. This drug should be Technician Tips
to prevent or treat histamine-associated dispensed only by veterinarians familiar Always aspirate skin and subcutaneous masses
gastric ulceration. with its indications and side effects. Ongoing because some masses that feel like lipomas are
○ For most MCTs, tumors should be surgi- patient monitoring and veterinary follow-up MCTs.
cally excised with 2 cm or greater lateral for response to therapy and monitoring for
margins and 1 fascial plane deep to the adverse effects is warranted. Client Education
tumor. Any new masses on the skin should be evaluated
○ All tissue should be submitted for his- PROGNOSIS & OUTCOME as soon as possible.
tologic evaluation of grade and margins.
Margins should be inked before placement • The most significant prognostic indicator SUGGESTED READING
in formalin. Perioperative complications for MCT is tumor grade. For dogs with Kiupel M, et al: Proposal of a 2-tier histologic grading
can include hypotension and hemorrhage. completely excised, low-grade MCTs, the system for canine cutaneous mast cell tumors to
Postoperative complications can include prognosis is excellent: only ≈5% of these more accurately predict biologic behavior. Vet
poor wound healing after resection of large tumors recur locally or metastasize. Pathol 48(1):147-155, 2011.
or infiltrative MCT. • For dogs with incompletely excised, low- AUTHOR: Tracy Gieger, DVM, DACVIM, DACVR
• For tumors that are not surgically resectable grade MCTs where additional surgery (scar EDITOR: Kenneth M. Rassnick, DVM, DACVIM
because of size, invasiveness, or metastasis, revision) is not possible, RT is the treatment
chemotherapy, targeted therapy, or RT before of choice, with 80%-90% of dogs free of
or instead of surgery may be indicated. tumor 2-5 years after treatment. If RT is not
• MCTs are responsive to RT. an option, careful monitoring with routine
○ Treating MCT in a microscopic disease exams is warranted. Benefit of treating
setting (i.e., postsurgical resection) yields dogs with incompletely excised, low-grade

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