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Mast Cell Tumor
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Mast Cell Tumor

Hello, my 1 year old Boston Terrier had surgery on Friday, 2/19/10 to remove a mass on the left side of her dorsolateral lumbar area.  It was biopsied and according to the pathology report the microscoping findings say that it was a Mast Cell Tumor, Low Grade 2. The vet suggested blood work every 6 months and x-rays once a year because she might get a tumor on her organs, said that her mitotic index is a 1 and that survival would be up to 70 months.  If she were to get another mass he would do surgery again but that it would most likely come back.  I was heartbroken with these news but just read that Boston Terriers get MCT all the time and they have a long and normal survival as long as the margin comes back clean.  The report states that the lateral surgical margins range form 0.5 to 0.7 cm and the deep margin was 0.4cm.  The mass is discrete, well circumscribed, nodular and appeared completely excised.  Does this mean that her margin is clean?  
It also states that the regional lymph node should be examined for any evidence of metastasis.  But my vet did not mention anything about that, he just said, "I will see you in 6 months for the blood tests".  I adopted my puppy from a  Boston Rescue group and they told me that MCT are very common on Bostons and that my Vet telling me that survival rate can be up to 70 months because her mitotic index is  a 1 is wrong.  Is this true?  I am so sad and scared.  Please advice.
Type of Animal
:  
Dog
Age of Animal
:  
1
Sex of Animal
:  
Female
Breed of Animal
:  
Boston Terrier
Last date your pet was examined by a vet?
:  
February 19, 2010
City
:  
Chino Hills
State/Province
:  
CA
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931217_tn?1283484935
Dear Hereta,

Mast Cell Tumors (MCT) typically are graded 1,2 or 3 with Grade 1 being the most benign and Grade 3 the most malignant. Grade 2 MCT which is very common, can go either way, having characteristics more like Grade 1 or like Grade 3. Mitotic index is a pathologists term and refers to the percentage of cells that were actively dividing at the moment the tissue sample was "fixed", which means killed and preserved. A higher index would presumably bring a worse prognosis. Mitotic Index of 5 or above is an unofficial cutoff between low risk Grade 2 and high risk Grade 2.

That said, most of us talk about "low" or "high" Grade 2 as the way to offer prognostic information to clients whose pets have MCT. "Low" Grade 2 implies to me that your dog's mass would more likely behave as a Grade 1, i.e. as a benign MCT.  The factors that are most important are: clean margins, Grade 2 or lower, and low MI . If the mitotic index on a cleanly excised Grade 2 MCT is low, no additional therapy is warranted.  Thus watching for recurrence rather than pursuing further treatment is indicated. If the margins were  demonstrably "dirty", I would recommend excision of the original surgical site to include a plane of tissue deep to the wound. Thus clean margins at the first surgery is important.

The likelihood of local recurrence is about 5% and the likelihood of spread to new sites is less than 5% when a clean margin is achieved with a first surgery. About 40% of dogs that develop more than 1 cutaneous MCT can develop even more over time, so regular rechecks and evaluation of any new masses is important. The long-term outlook for these dogs is still very good, as long as each tumor that pops up is dealt with appropriately. I think 70 months, or any set period of time in this case, is overly pessimistic.

The below abstract talks about prognosis with recurrence. While it is written in medical terminology, note the conclusions. I hope it will help ease your mind.

J Am Vet Med Assoc. 2006 Jan 1;228(1):91-5.
Evaluation of prognostic factors associated with outcome in dogs with multiple cutaneous mast cell tumors treated with surgery with and without adjuvant treatment: 54 cases (1998-2004). Mullins MN, Dernell WS, Withrow SJ, Ehrhart EJ, Thamm DH, Lana SE.

Animal Cancer Center and Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523, USA.

OBJECTIVE: To evaluate prognostic factors associated with outcome of dogs with multiple cutaneous mast cell tumors (MCTs) treated with surgery with or without adjuvant treatment. DESIGN: Retrospective case series. ANIMALS: 54 dogs with a minimum of 2 simultaneous, histologically confirmed cutaneous MCTs that had been excised and had adequate staging and follow-up data. PROCEDURE: Medical records from 1998 to 2004 were examined. Outcome was assessed with the Kaplan-Meier product-limit method and log-rank analysis. Prognostic factors evaluated included signalment; number, histologic grade, location, size, local recurrence, and de novo development of MCTs; quality of surgical margins; clinical signs at the time of diagnosis; and use of adjuvant treatment. RESULTS: Medical records of 54 dogs with 153 tumors were included. Median follow-up time was 658 days. Median disease-free interval (1,917 days; range, 11 to 1,917 days) and median survival time (1,917 days; range, 14 to 1,917 days) were not yet reached. The 1- year and 2- to 5-year survival rates were 87% and 85%, respectively. The overall rate of metastasis was 15%. Factors that negatively influenced survival time in the univariate analysis included incomplete excision, local recurrence, size > 3 cm, clinical signs at the time of diagnosis, and use of adjuvant treatment. Presence of clinical signs at the time of diagnosis was the only negative prognostic factor for disease-free interval detected in the multivariate analysis. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that multiple cutaneous MCTs in dogs are associated with a low rate of metastasis and a good prognosis for long-term survival with adequate excision of all MCTs.

Sincerely,

Arnold L. Goldman DVM, MS
medHelp & PDOC
5 Comments
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Avatar_f_tn
Hello, thank you so much for you quick reply. I am definitely more at ease now.
I really appreciate the way you put everything in words so that a normal person can actually understand.  

I had a quick question though and would like your input, I know you dont' give out medical advice.

The vet told me that my boston terrier needs to get blood work every 6 months and xrays yearly to make sure that no MCT's appear internally.  I was told by the Rescue group who have experience with Bostons who get MCT that this is not necessary for the chances of a boston getting MCT on an organ is low.  Since she had clean margins and she's a low grade 2 would follow up every 6 months be necessary or is me checking her for any other masses on her body sufficient enough?
Once again, thank you.
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931217_tn?1283484935
Hi again,

How frequently to perform minimum database type blood work is a judgment call for each of us. More importantly with Mast cell disease is a thorough physical examination to observe for recurrence at the original site or new tumors. Every six months is a reasonable compromise for this latter service. I usually would recommend annual blood work rather than every six months in a dog just 1 year old, though, your vetrinarian may have a reason I have not discerned here.  If the dog was older, say 7, then it makes more sense to me to look that closely every 6 months.

Best to you,

Dr G
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Avatar_m_tn
Hello, I was just curious what the cost of this operation was? It seems my dog has a tumor on his ear :(

thanks
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Avatar_f_tn
hi,
well the total cost was $500 that was for anesthesia, blood work, biopsy, and the mass removal.  

hope your dog is ok.

Hereta
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