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CELL TUMORS IN DOGS
Bath-Brunswick Veterinary Associates, Inc.
Dr. Gail D. Mason, DVM, MA, DACVIM
cell tumors (MCT 's) are fairly common tumors in dogs. They are
most frequently found in the superficial layers of the skin, on
any part of the body. Frequently, there will be ulceration over
the area of the tumor, and the dog may scratch or bite at the affected
area. The appearance of the tumor does not reveal its potential
for spread or recurrence with any certainty. The tumors are usually
singular, but dogs may present with multiple nodules, or recurrent
ones. Some nodules occasionally enlarge and then regress in size
on their own, due to swelling within the tumor itself. This should
always raise the suspicion of the presence of an MCT.
OF MAST CELL TUMORS
cell tumors do not have a specific appearance. However, they are
fairly easily detected by a "needle aspirate and cytology." Insertion
of a small needle into the tumor (virtually painless) area is followed
by examination of the cells under a microscope. Mast cells are large,
round cells that usually have dark granules in them. The granules
contain substances which, when released, cause swelling, itching,
and redness. Infrequently, when a large number of granules discharge
their chemical contents into the bloodstream, vomiting, stomach
ulcers, shock and even death may result.
cell tumors can be somewhat unpredictable in their behavior, relative
to other types of tumors in dogs. Because of this, care is taken
to "grade" the tumors that are discovered. The grade reflects the
degree to which the malignant mast cells differ from normal, non-malignant
mast cells. The stage can generally be correlated with tumor behavior,
tumor recurrence, and survival of the patient. Mast cell tumors
affecting the limbs, head, or neck tend to correlate with a more
favorable prognosis than those found on the trunk or groin. Multiple
mast cell tumors or those exhibiting rapid growth tend to have a
more guarded prognosis. A pathologist determines the tissue grade
of the tumor after the tumor is biopsied or removed.
I: well-differentiated-25% recurrence rate post-surgery
II: moderately differentiated-44% recurrence rate post-surgery
III: poorly differentiated-76% recurrence rate post-surgery
FOR MAST CELL TUMORS
for mast cell tumors may involve surgery (the mainstay), chemotherapy,
and/or radiation therapy. Recommendations for treatment are based
on the type and grade of the tumor, surgical feasibility, and the
presence or absence of spread (dissemination) of malignant mast
cells throughout the body. Your veterinarian will usually submit
blood tests and request abdominal ultrasound or radiographs (x-rays)
to determine the likelihood of malignant mast cells elsewhere in
the dog 's body. Bone marrow biopsies are no longer routinely done,
as they have not shown to have high predictive value for tumor staging.
single mast cell tumors, a surgical procedure known as a "wide resection"
is performed. This means aggressively excavating the tumor and surrounding
tissues so that at least 3 cm of normal tissue in all directions
is removed. The margins of the removed tissue are examined by a
pathologist to determine the presence of any lingering malignant
cells. If negative, we refer to it as "clean margins". If the pathologist
suspects the presence of mast cells in the remaining tissues of
the surgery site, we refer to it as "dirty margins".
aggressive surgery early in the course of mast cell tumor disease
is associated with the best overall prognosis. A grade I or II tumor
that has been completely removed usually requires no other immediate
therapy. A grade III tumor, multiple tumors, recurrent tumors, or
tumors with dirty margins (those which for anatomical reasons could
not be subjected to further surgery) often require follow-up or
therapy is an option for dogs whose mast cells tumors are localized,
but too large for a clean resection or in an area difficult to resect
such as tissues of the facial region, or as follow-up therapy for
tumors with dirty margins. Dogs tolerate radiation therapy well,
and it can offer long-term control for these tumors. Radiation therapy
would not be appropriate for dogs with multiple tumors or those
with evidence of disease throughout the body since the radiation
beam treats only a single focus of disease.
denotes the administration of certain anti-cancer drugs in order
to delay/prevent tumor growth or spread. It may be used before or
after surgery, or alone.
(a cortisone) is the most commonly used drug for therapy of mast
cell tumors. It is well tolerated by dogs and is usually employed
for a minimum of six months. If no new tumors appear within that
time, your doctor may wean your dog off the prednisone completely.
The side effects of prednisone include weight gain, increased appetite
and thirst, bladder or skin infections, and panting. Occasionally,
stomach irritation or ulcers can occur, or inflammation of the pancreas.
Most of the time, the drug dose can be titrated to the patient to
minimize any overt symptoms. If the tumor type is determined to
be aggressive, additional drugs such as stomach protectants may
be prescribed to guard against untoward tumor effects.
recurrent or multiple tumors, and for those tumors that cannot be
surgically removed, combination chemotherapy can be effective in
controlling tumor growth and spread for weeks to months or more.
A cure per se is generally not realistic, but many dogs tolerate
therapy extremely well. The 6-month protocol involves:
high dose at first, then taper over 4 months
an outpatient injection, given once every 21 days
¨: an oral chemotherapy drug, given by the owners on days
8,9,10, and 11 of a 21-day cycle.
side effects of prednisone are discussed above. Vinblastine and
Cytoxan have the ability to cause nausea and or vomiting, though
this is not usual. The most important possible side effects are
lowering the body's defenses so that frequent infections occurs,
or (rarely) causing many mast cells to release their contents at
once. Both situations can be life threatening. However, these are
NOT common, and the risk of these is significantly lower than the
risk of untreated mast cell disease. You will be given instructions
on what to do if any side effects occur, so do not hesitate to contact
is a potent oral chemotherapy drug that can be used once every three
weeks in patients who MCT's have become resistant to other treatments.
It is very well tolerated in general. However, because it can increase
the risk of infection (especially seven days after it is given),
any noted fever, depression, weakness, or refusal to eat should
be reported to us immediately. Infection is almost always completely
factors that are known to influence patient outcome are grade of
tumor (I is best, III is most dangerous), completeness of surgical
removal (clean margins), and tumor location. Dogs with high-grade
tumors, multiple or recurrent tumors, or evidence of spread to the
bloodstream or to other organs have a much more guarded prognosis
for a lengthy survival.
patient monitoring is essential in dogs with a history of mast cell
tumors. As with many tumors, early detection and treatment increases
the chances of successful treatment. You may be asked to have your
dog examined every 6-8 weeks following surgery, or every 21 days
during chemotherapy. Blood tests and/or needle aspirates are often
requested to assess tumor control. Any time you suspect a new or
recurrent tumor, or your dog is physically ill, contact us immediately.
We welcome the opportunity to help you and your dog in any manner
Mast cell tumors in dogs; In: Managing The Veterinary Cancer Patient;
Ogilvie, OK and Moore, As. © 1995 Veterinary Learning Systems. Trenton,
on protocol published by Elnsslie, Robin; published in the Veterinary
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