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Mast Cell Tumors in Dogs
TEXTBOOK OF VETERINARY INTERNAL MEDICINE
Client Inforniation Series
Mona P. Rosenberg
Mast cell tumors are common on or just under the skin of dogs. Any breed of dog can develop a mast cell tumor (MCT), but certain breeds are predisposed, including Boxers, bulldogs, pugs, Boston terriers, golden retrievers, and cocker spaniels. Mast cells are normal cells within the body that are responsible for responding to allergic reactions. For example, if you are slung by a bee and the area becomes red, hot, and itchy, it does so because mast cells infiltrate into the area, releasing a variety of substances including histamine, causing these symptoms. Other than hereditary factors, we do not know why dogs develop these tumors.
Your veterinarian may have diagnosed this tumor on the basis of a procedure called fine-needle aspiration. This is a minimally invasive technique that involves sticking a needle into the tumor, sucking a few cells out, and smearing the cells on a slide for a pathologist to evaluate under a micro-scope. This procedure is not painful to your dog and allows us to make a diagnosis in most cases. It does not, however, allow us to predict the biologic behavior of ("prognose") MCTs; surgical removal of the tumor followed by the use of a grading system is required. Location of the MCT is also of prognostic significance.
Knowing that we are dealing with an MCT before surgery can be helpful, because MCTs are notorious for sending out long, finger-like projections of cells into the surrounding tissue. This means we must surgically remove a wider margin of "normal" tissue surrounding any visible tumor in an attempt to remove all the microscopic "fingers."
Grade I or well-differentiated MCTs are the least aggressive of the three classes. If we are able to surgically excise the entire tumor (the pathologist will comment that the margins of tissue removed are "clean" or free of cancer cells), the incidence of recurrence is typically small, with 93 per cent of dogs being disease free at 1 year. "Metastasis" or spread of this form of MCT to distant, internal locations is unusual.
Grade II or intermediately differentiated MCTs are more aggressive than their grade I counterparts. An as yet unidentified percentage of dogs with this form of MCT develop metastasis of their cancer to intemal organs, typically to the bone marrow, spleen, or local lymph node. Provided there has been no spread of the cancer, 50 per cent of dogs with completely excised grade II or intermediately differentiated MCTs develop recurrence within 10 months of diagnosis; if no recurrence is detected in this period of time, there is a very good chance that the dog will survive for 5 years free of tumor.
Grade III or poorly differentiated MCTs carry a very poor prognosis, with 97 per cent of dogs succumbing to their cancer by 1 year. This is due to the high rate of metastasis or spread of the cancer to internal organs.
Mast cell tumors in the groin behave similarly to grade III MCTs, regardless of their histologic grade. It is not currently understood, but a high potential for metastasis has been consistently observed. Some oncologists believe that MCTs in the armpits and mucocutaneous junctions (e.g., lip margins, vulva, anus) can be quite malignant as well.
Once a dog is diagnosed with a MCT, several diagnostic tests are recommended. First, a complete blood count, bio-chemical profile, and urinalysis are performed to ensure that your dog exhibits no negative effects of the cancer in his or her system. Sometimes, a blood test called a buffy coat test is performed. This test looks for mast cells circulating through the bloodstream. This test is useful if it is positive, but it is often negative even if the cancer has spread; thus, it is not very sensitive.
The next step is to grade the cancer if this has not yet been done. Again, this can be done only by surgically removing all or part of the tumor. Once the tumor grade is known, a decision regarding further testing and treatment can be made. If the local lymph node is enlarged, it will be aspirated to look for cancer cells. If the MCT has been graded as intermediate or poorly differentiated (grade II or III), aspiration of the bone marrow and the spleen is advised. This is the most sensitive technique for determining whether the cancer has metastasized. Unfortunately, dogs with mast cell cancer in the bone marrow or the spleen have a very poor prognosis; many dogs live only 90 days from the time of diagnosis because of the effects of the cancer cells on the body. Sometimes, even in dogs with advanced disease, treatment can improve both the quality and quantity of life.
Your veterinarian may refer you to a cancer specialist for the testing or further discussion of your options for treatment.
Treatment for dogs with MCTs is dependent on the grade of tumor and results of testing. Dogs with grade I tumors that have been completely excised (removed) are not typically treated with any additional therapy. The "gold standard" of treatment for dogs with grade II MCTs, because of their moderate incidence of local recurrence even with complete surgical excision, is radiation therapy.
We also recommend using radiation therapy to treat grade I and II tumors that cannot be completely excised, provided there is no evidence of metastasis. Eighty-eight per cent of dogs with incompletely excised grade II tumors survive for 5 years without disease when treated with radiation therapy.
For dogs with grade III MCTs, dogs with MCTs in the groin, or dogs that have been diagnosed with systemic spread of their mast cell cancer, drug therapy is often recommended. These drugs include diphenhydramine (Benadryl) and cimetidine (Tagamet) to counteract the effects of histamine on the body and prednisone and other chemotherapy drugs to attempt to kill the cancer cells.
These drugs are usually well tolerated by dogs. Signs of terminal stages of the cancer include lethargy and gastrointestinal signs such as vomiting, diarrhea, and poor appetite.
Our goal for all cancer patients is that their quality of life be excellent; we never want the treatment to be worse than the disease. This goal is often achieved by working as a close team with your veterinarian and often a board-certified cancer specialist
Mast Cell Tumors
This page is about
Mast Cell Tumors
On other pages, I have information about other types of cancer in pets:
Lymphoma: one of the most common types of cancer we see in pets
Mammary Cancer
FibroSarcomas
Lipomas (Benign Fatty Masses)
Squamous Cell Carcinoma (Often on the ears of white cats) (Solar Cancers)
Granulomas
Joke Time:
Southern Football vs. Northern Football
Planning for the fall football season in the South is radically different from up North.
For those who are planning a football trip in the South, here are some helpful hints.
Women's Accessories:
NORTH: ChapStick in back pocket and a $20 bill in the front pocket.
SOUTH: Louis Vuitton duffel with two lipsticks, waterproof mascara, and a fifth of bourbon. Money not necessary - that's what dates are for.
Stadium Size:
NORTH: College football stadiums hold 20,000 people.
SOUTH: High school football stadiums hold 20,000 people.
Fathers:
NORTH: Expect their daughters to understand Sylvia Plath.
SOUTH: Expect their daughters to understand pass interference.
Campus Decor:
NORTH: Statues of founding fathers.
SOUTH: Statues of Heisman trophy winners.
Homecoming Queen:
NORTH: Also a physics major.
SOUTH: Also Miss America.
Heroes:
NORTH: Rudy Guliani
SOUTH: Archie & Payton Manning, Bo Jackson, Joe Namath, Lee Roy Jordan, Pat Dye, Bobby Bowden, Terry Bradshaw, I could go on,..but you get the point...
Getting Tickets:
NORTH: 5 days before the game you walk into the ticket office on campus and purchase tickets.
SOUTH: 5 months before the game you walk into the ticket office on campus and put name on waiting list for tickets. More like two years...
Friday Classes After a Thursday Night Game:
NORTH: Students and teachers not sure they're going to the game, because they have classes on Friday.
SOUTH: Teachers cancel Friday classes because they don't want to see the few hungover students that might actually make it to class.
Parking:
NORTH: An hour before game time, the University opens the campus for game parking.
SOUTH: RVs sporting their school flags begin arriving on Wednesday for the weekend festivities. The really faithful arrive on Tuesday.
Game Day:
NORTH: A few students party in the dorm and watch ESPN on TV.
SOUTH: Every student wakes up, has a beer for breakfast, and rushes over to where ESPN is broadcasting "Game Day Live" to get on camera and wave to the idiots up north who wonder why "Game Day Live" is never broadcast from their campus.
Tailgating:
NORTH: Raw meat on a grill, beer with lime in it, listening to local radio station with truck tailgate down.
SOUTH: 30-foot custom pig-shaped smoker fires up at dawn. Cooking accompanied by live performance by "Dave Matthews Band," who come over during breaks and ask for a hit off bottle of bourbon.
Getting to the Stadium:
NORTH: You ask "Where's the stadium?" When you find it, you walk right in.
SOUTH: When you're near it, you'll hear it. On game day it becomes the state's third largest city.
Concessions:
NORTH: Drinks served in a paper cup, filled to the top with soda.
SOUTH: Drinks served in a plastic cup, with the home team's mascot on it,filled less than half way with soda, to ensure enough room for bourbon.
When National Anthem is Played:
NORTH: Stands are less than half full, and less than half of them stand up.
SOUTH: 100,000 fans, all standing, sing along in perfect four-part harmony.
The Smell in the Air
After the First Score:
NORTH: Nothing changes.
SOUTH: Fireworks, with a touch of bourbon.
Commentary (Male):
NORTH: "Nice play."
SOUTH: "Dammit, you slow sumbitch - tackle him and break his legs."
Commentary (Female):
NORTH: "My, this certainly is a violent sport."
SOUTH: "Dammit, you slow sumbitch - tackle him and break his legs."
Announcers:
NORTH: Neutral and paid.
SOUTH: Announcer harmonizes with the crowd in the fight song, with a tear in his eye because he is so proud of his team.
After the Game:
NORTH: The stadium is empty way before the game ends.
SOUTH: Another rack of ribs goes on the smoker. While somebody goes to the nearest package store for more bourbon, planning begins for
next week's game.
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