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Canine Mast Cell Tumors
by Janet
Peterson, DVM, DACVIM (oncology)
Mast cell tumors are a relatively
common tumor (especially involving the skin) in dogs. They can
“masquerade” and look like many other tumor types. They can vary
from relatively small and insignificant tumors to very
aggressive, large and lethal tumors.
The most important diagnostic is a fine needle aspirate and
cytology of the mass to
assist in surgical planning, although grading cannot be
accomplished without
histopathology. Other recommended presurgical diagnostics
include
routine CBC, chemistry profile, and urinalysis, and abdominal
ultrasound. Diagnostics that might be considered include fine
needle aspirate and cytology of the draining lymph nodes, chest
x-rays (primarily to look for lymphadenopathy), and a bone
marrow.
Even with grading and extensive testing, it can be difficult to
predict how these tumors will behave in an individual patient.
With the traditional grading system, there are three grades (I,
II, and III) of mast cell tumor which can roughly predict the
behavior of the tumor (I being the most benign form of the
tumor). There is a newer histologic grading system simplifying
the categories to a high and low grade. Additionally, there is
an additional panel of stains which may assist in more
accurately predicting the aggressive nature of a particular mast
cell tumor. This may be especially helpful with some mast cell
tumors in terms of prognosis and possible adjunctive treatment
considerations.
Aggressive surgery is often the primary treatment consideration
for mast cell tumors and may be considered curative for grade I
mast cell tumors and some grade II mast cell tumors (with
adequate margins---greater than 0.5 to 1 cm). Radiation therapy
might also be considered.
Recent advances in chemotherapy have also occurred. There are
now two relatively
new veterinary chemotherapy drugs available which are both very
promising:
Palladia™ (toceranib phosphate) and Kinavet CA1® (masitinib
mesylate). Candidates for this type of chemotherapy typically
include dogs with higher grade mast cell tumors and dogs with
multiple mast cell tumors. These drugs are receptor tyrosine
kinase (RTK) inhibitors. Inhibition of RTKs on endothelial
cells, pericytes, and tumor cells disrupts multiple processes
necessary for tumor growth.
Palladia inhibits the activity of VEGFR-2, an RFK expressed on
endothelial cells. It inhibits the activity of PDGFR-B,an RTK
expressed on pericytes and inhibits the RTK KIT on tumor cells.
KIT is commonly dysregulated in canine MCT. Other chemotherapy
considerations in these situations might include vinblastine,
CCNU (lomustine), and prednisone. Label information on the
veterinary drugs is provided by the manufacturer.
https://animalhealth.pfizer.com/sites/pahweb/US/EN/Products/
PublishingImages/Palladia_PI.pdf
http://www.kinavet.com/
Consultation with a veterinary
oncologist may be helpful in diagnosis and management of mast
cell neoplasia. To locate a veterinary oncologist in Maryland
please reference the MVMA’s specialist locator
http://www.mdvma.org/ or
resources offered by the American College of Veterinary Internal
Medicine
http://acvim.org/websites/acvim/index.php?p=3. |
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Important
Links from this article
Palladia Toceranib
Phosphate Tablets
Kinavet
MVMA Specialist Locator
American College of
Veterinary Internal Medicine
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