Mast cell tumor with low-grade malignancy in dog

I noticed a small growth on the neck of my 10-year-old Boston terrier and took him to the vet last week to have it checked.  The growth was removed under local anesthesia and a specimen was sent to the lab.  No margins were removed.  The vet called me today to report that the growth was a mast cell tumor with a low-grade malignancy.  She did not recommend additional surgery to remove the margins--only that I check carefully for new growths.

My dog previously had a growth removed from near his ear about 8 years ago.  It was removed surgically under general anesthesia.  Margins were also removed.  The subsequent lab report also indicated a mast cell tumor with low-grade malignancy.

I certainly don't want to subject my dog to unnecessary surgery, but I'm very anxious about leaving the margins surrounding what had been a tumor with a low-grade malignancy.  I would very much appreciate your opinion about what the best course of treatment would be.  

[Arnold L Goldman, D.V.M.]

Hi Emanuelle,

Mast cell tumors of each grade have distinct behavior. If by "low grade" you mean grade one, then complete surgical excision should be curative.

In general grade is reflective and predictive for probable biologic behavior (metastatic or non-metastatic). The three grades are as follows:

    * Grade I: Well-differentiated and mature: Almost all of these tumors remain locally confined and complete surgical resection should be curative.
    * Grade II: Intermediate differentiated: Most of these tumors remain locally confined and complete surgical resection should be curative. However, a small percentage of these tumors can be aggressive with early metastasis to regional and distant sites.
    * Grade III: Anaplastic or undifferentiated: Most of these tumors have an aggressive phenotype and metastasize early in the disease course, making curative surgical procedures unlikely.

You say that no margins were removed, but that would be impossible as surgery was done and the mass removed. The distance from the cut edge of the tissue to the obvious tumor edge IS the margin. If you mean a WIDE margin was not taken at that time or that the margin itself was NOT ANALYZED for the presence of tumor cells in the margin (implying that some cells may have been left behind on the "other side", i.e. the PET side of the site of the original mass, then I understand what you mean.

Whether the site should be re-operated would depend on grade and whether the margin, no matter how thin or thick was clean. In a low grade MCT, a grade 1 say, then probably there is no need to do so if the tumor was grossly excised with at least a minimal margin. In a grade 2, perhaps the surgical site should be excised, wide and deep, to ensure all gross tissue was removed. This can be taken as a second surgical step.

You need to find out what the histologic grade was. If it was a 1, then you are probably OK to observe and wait. It is common for dogs to get multiple mast cell tumors, either sequentially or simultaneously. These should be regarded as separate events unless you have compelling evidence of metastasis (e.g. turns up in adjacent lymph node, multiple new tumors turn up at once). Each individual new MCT should be treated in the same way, with surgery with wide margins and histopathology for grade and margins, and the veterinarian should warn you about the risk of future new tumors so you do not become unduly concerned with each one.

Hope this helps! PS I have 4 Boston terriers. Hap is the one in the photo with me above.

Sincerely,

Arnold L. Goldman DVM, MS
MedHelp & PDOC

[Emanuelle]

Thank you so much for your quick response.  I assume that my dog's MCT was grade 1, but I will call tomorrow to inquire about the grade.  I'll also ask whether the margin was clean.  The vet did not volunteer this information, and I was not knowledgeable enough to ask.  Your response was very helpful to me.

BTW, those are great ears on Hap!

[Emanuelle]

The MCT was less than 1 centimeter and was completely removed.  It was grade II (low).  (I was told that grade II MCTs were classified low-medium-high.)  The margin was clean.  The vet seemed quite confident that no further treatment was needed.  She felt that the risk of anesthesia outweighed the potential benefit of further surgery.  My dog is healthy for a 10-year-old Boston (slight heart murmur but no other health problems noted during his recent geriatric physical), and he had no problems with general anesthesia for a tooth extraction last September.  The MCT removed 8 years ago was also a grade II (low).

I'm inclined to go with my vet's recommendation, but I would really appreciate knowing your opinion.

Many thanks!  

[Arnold L Goldman, D.V.M.]

Hi again,

I agree with what you have been advised, completely. As you have learned, Grade 2's can go either way and your doctor's pathologist has determined your dog's mass fell on the low end of grade 2. These grades are determined based on microscopic criteria, so the pathologist must be trusted to call it one way or the other. With a "clean margin" as determined by the pathologist there is little reason to pursue or worry about this further.

Best regards to you and your dog,

Arnie Goldman