Mr.Billfold
12-23-2007, 08:41 PM
WHAT IS A MAST CELL? A normal mast cell is part of our immunologic defense systems against invading organisms. Mast cells are meant to participate in the war against parasites (as opposed to the war against bacterial or viral invaders). They are bound within tissues that interface with the external world such as the skin, respiratory or intestinal tract. They do not circulate through the body.
The mast cell possesses within itself granules of especially inflammatory biochemicals mean for use against invading parasites. (Think of these as small bombs that can be released). The mast cell has binding sites on its surface for a special type of antibody called “IgE.” IgE is produced in response to exposure to antigens typical of parasites (i.e. worm skin proteins, or similarly shaped proteins). IgE antibodies find their way to a tissue mast cell and perch there. With enough exposure to the antigen in question, the mast cell may be covered with IgE antibodies like the fluff of a dandelion. The mast cell is said, at this point, to be “sensitized.”
http://www.marvistavet.com/assets/images/IgE_antibodies.gifThe IgE antibodies are “Y” shaped. Their foot is planted in the mast cell while their arms lift up hoping to capture their antigen. When the antigen comes by and is grasped by the IgE antibodies, this should indicate that a parasite is near and the mast cell, like a land mine, degranulates releasing its toxic biochemical weapons. These chemicals are harmful to the parasite plus serve as signals to other immune cells that a battle is in progress and for them to come and join in. At least this is what is supposed to happen.
We live in a clean world without a lot of parasites. What unfortunately tends to happen is that the IgE/mast cell system is stimulated with other antigens that are of similar shape or size as parasitic antigens. These “next best” antigens are usually pollen proteins and the result is an allergy. Instead of killing the invading parasite, the mast cell biochemicals produce local redness, itch, swelling, and other symptoms we associate with allergic reactions.
AND THE MAST CELL TUMOR?
As if the mast cell isn’t enough of a troublemaker in this regard, the mast cell can form a tumor made of many mast cells. When this happens, the cells of the tumor are unstable. This means they releases their toxic granules with simple contact or even at random creating allergic symptoms that do not correlate with exposure to any particular antigen.
Mast cell tumors are notoriously invasive and difficult to treat.
CANINE
Mast cell tumors are especially common in dogs accounting for approximately one skin tumor in every five. The Boxer is at an especially high risk as are related breeds: English Bulldog, Boston Terrier). Also at higher than average risk are the Shar pei, Labrador Retriever, Golden Retriever, Schnauzer, and Cocker Spaniel. Most mast cell tumors arise in the skin but technically they can arise anywhere that mast cells are found. The mast cell tumor does not have a characteristic appearance though because of the tumor’s ability to cause swelling through the release of granules, it is not unusual for the owner to notice a sudden change in the size of the growth or, for that matter, that the growth is itchy or bothersome to the patient.
Diagnosis can often be made by aspirating some cells of the tumor with a needle and examining them under the microscope. The granules have distinct staining characteristics leading to their recognition. An actual tissue biopsy, however, is needed to grade the tumor and grading of the tumor is crucial to determining prognosis.
GRADING THE MAST CELL TUMOR
Mast cell tumors are graded by the pathologist when the biopsy sample is read. The Grade is a reflection of the malignant characteristics of the cells under the mircoscope (which of course generally correlates to the behavior of the tumor) with Grade 1 being benign, Grade 3 being malignant, and Grade 2 having some ability to go either way.
GRADE I TUMORS
This is the best type of Mast Cell tumor to have. While it may tend to be larger and more locally invasive than may be visually apparent, it tends not to spread beyond its place in the skin. Surgery should be curative. If the original biopsy sample shows that the tumor has only narrowly been removed or that the tumor extends to the margins of the sample, a second surgery should promptly be done to get the rest of the tumor if at all possible. If the Grade I Mast Cell tumor is incompletely excised it will grow back in time; it is best to get it all and be done with it as quickly as possible. About half of all Mast Cell tumors are Grade 1 tumors and can be cured with surgery alone.
GRADE III TUMORS
This is the worst type of Mast Cell tumor to have. Grade III tumors account for approximately 25% of all mast cell tumors and they behave very invasively and aggressively. If only surgical excistion is attempted without supplementary chemotherapy, a mean survival time of 18 weeks (4-5 months) can be expected.
GRADE II TUMORS
This type of tumor is somewhat unpredictable in its behavior. Recent studies have shown that radiation therapy administered to the site of the tumor can cure >80% of patients as long as the tumor has not already shown distant spread.
The mast cell possesses within itself granules of especially inflammatory biochemicals mean for use against invading parasites. (Think of these as small bombs that can be released). The mast cell has binding sites on its surface for a special type of antibody called “IgE.” IgE is produced in response to exposure to antigens typical of parasites (i.e. worm skin proteins, or similarly shaped proteins). IgE antibodies find their way to a tissue mast cell and perch there. With enough exposure to the antigen in question, the mast cell may be covered with IgE antibodies like the fluff of a dandelion. The mast cell is said, at this point, to be “sensitized.”
http://www.marvistavet.com/assets/images/IgE_antibodies.gifThe IgE antibodies are “Y” shaped. Their foot is planted in the mast cell while their arms lift up hoping to capture their antigen. When the antigen comes by and is grasped by the IgE antibodies, this should indicate that a parasite is near and the mast cell, like a land mine, degranulates releasing its toxic biochemical weapons. These chemicals are harmful to the parasite plus serve as signals to other immune cells that a battle is in progress and for them to come and join in. At least this is what is supposed to happen.
We live in a clean world without a lot of parasites. What unfortunately tends to happen is that the IgE/mast cell system is stimulated with other antigens that are of similar shape or size as parasitic antigens. These “next best” antigens are usually pollen proteins and the result is an allergy. Instead of killing the invading parasite, the mast cell biochemicals produce local redness, itch, swelling, and other symptoms we associate with allergic reactions.
AND THE MAST CELL TUMOR?
As if the mast cell isn’t enough of a troublemaker in this regard, the mast cell can form a tumor made of many mast cells. When this happens, the cells of the tumor are unstable. This means they releases their toxic granules with simple contact or even at random creating allergic symptoms that do not correlate with exposure to any particular antigen.
Mast cell tumors are notoriously invasive and difficult to treat.
CANINE
Mast cell tumors are especially common in dogs accounting for approximately one skin tumor in every five. The Boxer is at an especially high risk as are related breeds: English Bulldog, Boston Terrier). Also at higher than average risk are the Shar pei, Labrador Retriever, Golden Retriever, Schnauzer, and Cocker Spaniel. Most mast cell tumors arise in the skin but technically they can arise anywhere that mast cells are found. The mast cell tumor does not have a characteristic appearance though because of the tumor’s ability to cause swelling through the release of granules, it is not unusual for the owner to notice a sudden change in the size of the growth or, for that matter, that the growth is itchy or bothersome to the patient.
Diagnosis can often be made by aspirating some cells of the tumor with a needle and examining them under the microscope. The granules have distinct staining characteristics leading to their recognition. An actual tissue biopsy, however, is needed to grade the tumor and grading of the tumor is crucial to determining prognosis.
GRADING THE MAST CELL TUMOR
Mast cell tumors are graded by the pathologist when the biopsy sample is read. The Grade is a reflection of the malignant characteristics of the cells under the mircoscope (which of course generally correlates to the behavior of the tumor) with Grade 1 being benign, Grade 3 being malignant, and Grade 2 having some ability to go either way.
GRADE I TUMORS
This is the best type of Mast Cell tumor to have. While it may tend to be larger and more locally invasive than may be visually apparent, it tends not to spread beyond its place in the skin. Surgery should be curative. If the original biopsy sample shows that the tumor has only narrowly been removed or that the tumor extends to the margins of the sample, a second surgery should promptly be done to get the rest of the tumor if at all possible. If the Grade I Mast Cell tumor is incompletely excised it will grow back in time; it is best to get it all and be done with it as quickly as possible. About half of all Mast Cell tumors are Grade 1 tumors and can be cured with surgery alone.
GRADE III TUMORS
This is the worst type of Mast Cell tumor to have. Grade III tumors account for approximately 25% of all mast cell tumors and they behave very invasively and aggressively. If only surgical excistion is attempted without supplementary chemotherapy, a mean survival time of 18 weeks (4-5 months) can be expected.
GRADE II TUMORS
This type of tumor is somewhat unpredictable in its behavior. Recent studies have shown that radiation therapy administered to the site of the tumor can cure >80% of patients as long as the tumor has not already shown distant spread.