Page 1426 - Clinical Small Animal Internal Medicine

1364 Section 11 Oncologic Disease

(a) (b)
VetBooks.ir

Figure 155.5 (a) A female boxer at presentation with over 300 dermal MCTs. (b) The same patient after two weeks of tyrosine
kinase therapy.

of 65%. The micellar prepared paclitaxel has shown The reported efficacy of Palladia is near 40%
promise against MCTs but is not yet commercially avail- (Figure 155.5). Palladia may be used for all grades of
able. The current formulation of paclitaxel (suspended in MCT but is more effective against MCTs with the
cremophor) has a marked increased risk of anaphylaxis known KIT mutation. The labeled dose of 3.25 mg/kg
during administration. every other day results in significant gastrointestinal
The tyrosine kinase receptor KIT is mutated and/or toxicity, myalgias, and neutropenia. Most clinical oncol-
overexpressed in up to 40% of MCTs. These tandem dupli- ogists now prefer a lower dose of 2.5–2.75 mg/kg on a
cation mutations at the juxtamembrane coding region Monday‐Wednesday‐Friday treatment schedule. Oral
result in the malignant behavior of cellular proliferation, famotidine and sucralfate may eliminate low‐grade nau-
adhesion, migration, and maturation. Consequently, KIT sea or anorexia. Diarrhea is routinely treated with stand-
mutations have been found more commonly in higher ard doses of loperamide. Protracted or severe clinical
grade MCTs. signs require a temporary discontinuation (drug holiday)
Recent advancements in MCT treatments have led to of the medication until clinical improvement. Routine
the development of tyrosine kinase inhibitors. These complete blood counts are recommended over the first
drugs block the effects of mutated KIT receptors six weeks of therapy. Therafter, a complete blood count
through competitive inhibition. Toceranib phosphate chemistry panel and urinalysis are recommended
(Palladia™, Zoetis) is the first FDA‐approved treatment approximately once every six weeks for patients that
for canine MCTs. It is labeled for the treatment of remain on tyrosine kinase inhibitors. Mild (grade I and
recurrent or nonsurgical high‐grade mast cell tumors. II) neutropenias are commonly noted and do not require
Additionally, masitinib (Kinavet®, AB Science) achieved additional therapy or dosing alterations. However,
European regulatory approval under similar label guide- patients should be monitored for progression.
lines but recently lost licensure by the FDA and is no Idiosyncratic elevations in liver enzymes, hypertension
longer available for use in the United States. and protein‐losing nephropathies are also reported.