Mast cell
tumours account for 25% of skin tumours in dogs. Some breeds, may
inherit these tumours. Individual lines of some breeds may be
more prone to mast
cell tumours than others. The age of affected dogs varies, but
the
average age is eight years old. Small tumours can be missed in
dogs
with long or dense coats. Some common, benign growths can be
similar in appearance to mast cell tumours.
Mast cell tumours first appear as solitary lumps on or under a dog's
skin, and may grow over just a few days. The size of such lumps
may vary - they can get smaller and then grow again. Surrounding
skin will
often be inflamed. Half of all growths tend to appear on the
trunk
of the dog's body. Though cell tumours can look like many other
tumours,
they can also resemble insect bites or an allergic reaction. The
lymph
nodes can swell, as can the liver and spleen.
Diagnosis of mast cell tumours is done by a fine needle aspirate or
biopsy, often followed by surgery to remove the mass. X-rays and
ultrasound scans may help to find other masses around the body, with
affected lymph
nodes often being removed. Chemotherapy or radiotherapy may be
advised
for repeated or widespread mast cell tumours - 20% of dogs with a
tumour
will later develop two or more unrelated tumours, which should be
removed.
Some tumours are benign; they will not spread and can simply be
removed. Where moderately aggressive tumours are removed, no
other treatment may be needed, but often another growth will appear
within 2 months. Opinions vary widely on how well dogs with the
most aggressive tumours fare. The prognosis is poor if one
spreads to other organs, as their function will be affected. Mast
cell tumours produce more widespread effects.
reprinted with kind permission from Alastair
Balmain
Deputy Editor:Shooting Times
& Country Magazine
Blue Fin Building, 110 Southwark Street SE1 0SU
Tel: 020 3148 4750
*************************
Mast
Cell Tumors in Dogs
Author: Clinical Oncology Service
Affiliation: Veterinary Hospital of the University
of Pennsylvania (VHUP)
January 11, 1998
Mast cells are a special type
of blood cell that is normally involved in the body's response
to allergens and inflammation. Sometimes, these cells can become
cancerous and develop into mast cell tumors. The most common locations
for these tumors are the skin, spleen, liver and bone marrow. They are
malignant tumors that have the ability to spread to other organs. Even
though we know a lot about mast cell tumors, it can be difficult to
predict how
they will behave in an individual dog.
Mast cells contain substances that could be released into the
bloodstream and potentially cause systemic problems. This would include
gastric ulceration, bleeding and allergic reactions (anything from
swelling around the tumor to life threatening shock). Therefore, we
often put
our patients on antihistamines, antacids and corticosteroids as part
of their treatment.
Most of the remaining information will focus on cutaneous (skin) mast
cell tumors because they are the most common type seen in dogs.
Cutaneous Mast Cell Tumors (Skin)
The skin is the most common site for mast cell tumors in the
dog.
They are usually located in the skin of the legs or body. These tumors
are locally aggressive and can also metastasize (spread) to other areas
of the body. The most common sites of spread are the lymph nodes, bone
marrow and spleen.
The initial evaluation of a dog with a mast cell tumor includes:
biopsy, complete blood count (CBC), serum chemistry profile,
urinalysis, buffy coat (this is a special test that looks for mast
cells in the blood stream), lymph node aspirate and an abdominal
ultrasound
(to look at the liver and spleen).
In some cases, we may also do a bone marrow aspirate to look
for mast cells there.
The pathologist assigns a "grade" to the tumor when he looks
at it under the microscope. We use the grade to help predict how the
tumor will behave. This influences both the prognosis (outcome) and
treatment plan. For example, low-grade tumors are unlikely to spread
so that complete surgical removal of the tumor may be the only
treatment
required. High-grade tumors have a very high chance of spreading so we
look very carefully for spread and consider using systemic therapy
(such
as prednisone) in addition to local therapy (such as surgery or
radiation).
Treatment Options
Treatment option for cutaneous mast cell tumors include surgery,
radiation therapy, chemotherapy and supportive care.
Surgery is usually our first treatment choice. Because these
tumors are invasive, the surgeon must remove the tumor with a large
margin of normal tissue both around and underneath it to ensure
complete
removal. Mast cell tumors are deceptive and sometimes what we can see
and feel represents only a small part of the tumor. Even when a large
margin is taken, sometimes tumor cells are still left behind. When this
occurs, additional treatment is needed, otherwise, there is the chance
that the tumor might return. Options include another surgery or
radiation
therapy. It may not be possible to do another surgery because of the
location
of the tumor (e.g. tumors on the leg are difficult to completely remove
because there is not much extra skin). In this case, radiation therapy
is a good alternative. Radiation therapy is very effective at
preventing local recurrence of these tumors.
It is important to remember that surgery and radiation therapy are
local treatments and have no effect on the spread of the tumor.
Chemotherapy can be beneficial in treating metastasis since it is a
systemic treatment. In the case of mast cell tumors, prednisone
(a corticosteroid or "cortisone") is one of the most effective
chemotherapy agents available. We will prescribe prednisone if we
either find metastasis or if there is a high likelihood of metastasis.
Most dogs are kept on prednisone for a 6-month period. If there is no
evidence of metastasis or recurrence by that time, the prednisone is
discontinued. There are some situations where we will recommend
prednisone for a longer period of time. The most common side effects of
prednisone include increased thirst, urination, appetite and panting.
Prednisone can also cause gastrointestinal upset and rarely, gastric
ulcers. However, we use a gradually decreasing ("tapering") dose of
prednisone to try
to minimize these side effects. We may also recommend other
chemotherapy drugs on an individual basis. Unfortunately, there are no
other chemotherapy drugs that are highly effective against these
tumors.
As mentioned above, we prescribe additional medications to prevent
tumor related side effects. These include an antihistamine (Benadryl)
and an antacid (usually Tagamet). We also ask that you watch your pet
closely for any problems such as vomiting (especially if there is fresh
blood), diarrhoea, loss of appetite or a very dark or black stool (this
is a sign of digested blood). If any of these signs occur, we ask that
you contact either VHUP or your local veterinarian.
The prognosis (outcome) for cutaneous mast cell tumors depends upon
several things including the "grade" of the tumor, the location
of the tumor and the presence of metastasis. Many of these tumors are
successfully treated if there is no evidence of spread at the
start of treatment. Any future "lumps" and "bumps" should be
evaluated with an aspirate because dogs that have had one mast cell
tumor are at greater risk for the development of additional mast cell
tumors. Early detection of these tumors will increase the likelihood of
successful treatment.
For those tumors that have already spread or that occur in locations
other than the skin (e.g. the spleen), the prognosis is guarded. The
goal of treatment for these patients is to maintain a good quality
of life for as long as we can by controlling symptoms caused by
the presence of mast cells in the body. Symptoms can include vomiting,
diarrhoea,
anorexia (loss of appetite) and lethargy (tiredness).
Unfortunately, most of these dogs will die within 6 months
because we can no longer control these symptoms.
The above information is simply
informational. It's intent is not to replace the advice of a
veterinarian nor to assist you in making a diagnosis of your pet.
Please consult with your own veterinarian for confirmation of any
diagnosis. Your pets life may depend on it.
