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Mast cells are one
of the white blood cells involved in body’s immune system, especially
the allergic reaction response. When certain materials (such as the
proteins associated with insect bites and stings) enter the body, Mast
cells are activated and release a number of chemicals (especially
histamine) which bring about local swelling, redness and inflammation.
These chemicals cause blood vessels to dilate and become more permeable
so that other inflammatory cells can enter the area of inflammation.
Mast cells are
found throughout the body. They are more concentrated in the skin,
spleen and lymphnodes in general.
Like any other cell
in the body, Mast cells can become cancerous. When this occurs, they can
create localized solid tumors, and/or can develop into circulating tumor
cells. Cancerous mast cells have a tendency to release their chemicals
randomly which can lead to problems throughout the body. In particular,
when mast cells release histamine, it can cause destruction of the
protective mucus layer in the stomach which can then lead to bleeding
ulcers. When solid mast cell tumors are traumatized (by bumping or
manipulation) they may release their chemicals which can lead to abrupt
swelling in the area. Sometimes, so many blood vessel dilating
chemicals are released that the blood pressure can collapse suddenly and
the pet may collapse.
How do we
diagnose Mast Cell Tumors?
Mast cells are
known as the great masqueraders of cancer cells. Any lump can
potentially be a mast cell tumor. The only way to diagnose the tumor is
by observing the abnormal mast cells in the tumor. This can be done by
aspirating a small amount of material from the lump and observing it
under a microscope. Alternately, when we remove tumors we typically
send them to the lab for analysis and the pathologists will make the
diagnosis.
What is the
prognosis if my pet has mast cell tumor?
Mast cell tumors
are found in 3 levels of severity. Grade one mast cell tumors look very
much like normal mast cells and when they are surgically excised, the
disease is often times cured. Whenever we excise a mast cell, we need
to have the pathologists check the margins of the tumor to make certain
that we got all the cells out. If the margins of the excised tissue
contain mast cells, then a second more radical surgery is indicated.
Grade II mast cells
are more aggressive than grade I tumors. They have a greater tendency
to spread to the local lymph nodes and into the body into the spleen,
liver or lungs. Therefore, when we receive a diagnosis of grade II or
III disease, then we need to do a series of tests to see if the tumor
has spread internally. This is accomplished by means of xrays of the
chest and belly, ultrasound guided aspiration of the spleen and a blood
test to check for circulating mast cells (buffy coat examination). If
we get clean margins on the pathology report and no evidence of internal
tumors from out testing, then the prognosis is not bad. The median
survival time for these patients is approximately 2 years. However,
recurrence of the tumors is not uncommon.
Grade III tumors
are very aggressive and tend to spread all over the body. They can be
very difficult to remove surgically.
Can Mast Cell
tumors be treated with medicine?
There are a number of different chemotherapy
protocols that can be used to help reduce recurrence of mast cell tumors
and to lessen the side effects related to the histamine release from the
tumors. Chemotherapy is considered in the face of Grade II or III
disease. All pets with mast cell disease are usually placed on
histamine blockers to help protect the stomach from ulceration.
Chemotherapy response rates vary with the severity of the initial
disease. Your veterinarian can discuss the statistics with you if the
need arises.
All pets with mast
cell disease should have comprehensive physical examinations 2-3 times
per year. Radiographs should be repeated at 4-6 month intervals to
check for internal disease.
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