Thank you for including such a comprehensive answer regarding mast cell tumors and for providing the link to the journal article on evaluation of prognostic factors.
My 7 year old Golden Retriever, Inca, was recently found to have two Grade 2 Mast Cell Tumors. She had 2 masses, one located on her muzzle (bottom of "chin") and the other on her bottom lip. She had surgery 2 days ago to remove the tumors. I have yet to see the pathology report, I just obtained the results from vet over the phone. I have been told that all margins are clean, and that both tumours are Grade 2 with mitotic index of 5. At this stage, he has suggested no further intervention, with regular physical examinations to be conducted to monitor for local recurrence. I am writing, however, to ask your opinion on whether there may be an indication for adjuvant treatment, such as prednisone, or local radiotherapy. Are either of these treatment modalities likely to improve prognosis (survival time)?
Inca is such an important part of our family and we want to do everything possible to give her the best chance at a long and happy life, no matter the cost.
Your opinion on this matter would be greatly appreciated.
You are experiencing the same frustration as I do when a MCT is judged to be Grade 2, in that they can "go either way." I hate unclear answers! Grade 1 is generally quite benign and Grade 3 quite malignant. Grade 2 can be either and the distinction is made based upon criteria that are technical and subtle. Mitotic index is a measure of how many cells are showing microscopic signs of active cell division in the viewed area of a microscope slide. A higher index is worse than a lower, 5 being a fairly low number.
Consider this however: a mass is removed and submitted in its entirety (if relatively small) in a jar of formaldehyde ( a preservative) to a laboratory. A trained technician, using specific criteria slices a "representative" very small piece of tissue from the larger sample and places it into a small plastic tray (1" x 1"). The tray is then put into a machine that further "fixes" (preserves) the tissue and then through a series of solutions, replaces all water in the tissue with alcohol. Then the alcohol is replaced with parafin, a waxy material that makes the tissue firm enough to be thinly sliced. This latter process is called "embedding" and is followed by "sectioning" (slicing) the tissue into thin layers which can be attached to thin glass microscope slides. This is the final step before the tissue can be viewed. The slices are so thin that light can pass through, and that is how they are evaluated by a board certified pathologist.
The point of explaining all this, is that a small sample of a small sample is what is viewed. As such pathologic diagnoses and diagnoses are subject to the caveat that areas of concern could be missed and so we must make decisions on imperfect information. Even margin evaluation is subject to sampling errors, thus the minimal need to continue observing indefinitely.
With a Grade 2 MCT, with clean margins and a low mitotic index, even when two are present in the same close area, you are likely safe to continue observing, as opposed to pursuing further treatment now. Remember too, that treatments are not without their own adverse effects. Balance must be struck between doing good and doing harm. Primum non nocere, the latin medical expression means "first do no harm." Sometimes its best to "dont just do something, stand there." Your veterinarian's approach sounds very reasonable to me.
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