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Featuring Demian Dressler, DVM and Sue Ettinger, DVM, Dip. ACVIM (Oncology), authors of The Dog Cancer Survival Guide

When to Avoid Chemo for Canine Mast Cell Tumors?

Updated: June 19th, 2019

There has been much online talk these days about dogs with mast cell tumors (read, Palladia) which are the most common canine cancer.

So I thought I’d just add some fuel to the fire and give my readers some overall guidelines about mast cell tumors and chemotherapy.

As many already know, these cancers come in different grades (1, 2 and 3).  Grade 1 are almost always benign, grade 2 are intermediate (some benign and some malignant) and grade 3 are universally malignant.

Your vet will give you the grade following receipt of the biopsy report, which is completed by a path lab after submission of tissue from the tumor.

Wide excision (removal of a large swath of normal-appearing tissue around the tumor) cures many mast cell tumors.  Pretty much all grade 1, and about 90% or so of grade 2 mast cell tumors are gone permanently after wide excision.  Grade 3 mast cell tumors are candidates for chemo and possibly radiation and more as they will often come back and spread even after surgery.

The tricky guys are those grade 2 mast cell tumors.  Since some behave like benign tumors and some like real cancers, what are we supposed to do?

Well, the key is in getting more information about your dog’s individual tumor. There are a couple of bits of information that are valuable that can help you predict the behavior of your dog’s grade 2 mast cell tumor.

The single most important one is called the  mitotic index.  This is the number of cells that are actually dividing seen by the pathologist under the microscope.

The magical cut off is somewhere around 5.  This means that if the tumor has a mitotic index of less than 5, it usually will behave less aggressively and in my opinion do not require surgery, as long as you have clean margins on the removed tumor.

More than 5?  We need to now consider hitting these guys with the full spectrum approach (diet, supplements, chemo, and other strategies discussed in The Dog Cancer Survival Guide).

You may read about other markers (kit, AgNORs, Ki67) but these are much less useful than mitotic index.  If the mitotic index is around 5 though,  consider these other markers for more data.

By the way, not all vets may know about this stuff, so remember to be your dogs primary health care advocate and speak up!  You vet is the one who has to order this testing of the biopsy specimen from your dog.

The squeaky wheel gets the oil!

Best to all,

Dr D

Leave a Comment

  1. Jan Shir on October 5, 2014 at 6:53 pm

    Thank you so much for writing this!!!

  2. onevoice1914 on September 23, 2014 at 4:20 am

    It gave me comfort to read your story. I am in the exact same situation with my boxer, he is 13 and has 2 -MCT on his side, eating well, still wants to play. It seemed more cruel to put him though all that during his last years. And actually thought it would do more damage at his age and speed up the process of the unenviable.

  3. Jason on October 30, 2013 at 2:50 pm

    Hi Dr., My 11 year old dog recently had a mast cell tumor removed that the pathologist described as a Grade 2 MCT with a mitotic index of 0 and clean margins. This seems to carry a fairly hopeful prognosis, but I wanted to ask whether preoperative prednisone could distort the mitotic index. Our dog had been on a low dose of prednisone for 10 days, ending 4 days before surgery (and 5-6 days before the pathology report was compiled). Is this mitotic index still a reliable measure?

  4. Jeannie G. on September 19, 2013 at 2:38 am

    Hi Dr.: We removed MCT, Grade 1, on my 13 year old dog, and another mass has just returned in the same general area (spine/back). Organs were CAT scanned and nothing else found. Margins were clean on the first MCT, and it presented differently than this new one (which is more like fatty tumor but firmer). We’re going for a biopsy on the new mass, so I wanted to just clarify your comment: ” …if the tumor has a mitotic index of less than 5, it usually will behave less aggressively and in my opinion do not require surgery, as long as you have clean margins on the removed tumor.”

    To clarify, if the mitotic index from the second mass is benign or less than 5, removal of the second mass may not be necessary in your opinion? (knowing this is not a diagnosis by you). If not, what surgery is not necessary?

    Thank you in advance!

    • DrSueCancerVet on September 29, 2013 at 3:48 pm

      Dr Sue here! =) All MCT should be removed, even if the mitotic index is low. I have written a series on MCT discussing grading, staging, surgery, chemo etc. In addition to mitotic index there are other important predictors. Please check out the series: You can start here:
      If the tumor cannot be removed, you could consider radiation or chemo. Another situation where I might not recommend surgery – multiple tumors at one time, like the dog I managed with greater than 10 MCT. She went on chemo.
      Good luck! All my best, Dr Sue

  5. Jennifer on February 11, 2013 at 2:01 pm

    Dr. Sue,
    Thank you for the information! I took Big Boy to a veterinarian oncologist last Wednesday and was given two options, chemo or amputation. Since chemo isn’t something we can financially afford we are going to go the other route. The oncologist didn’t say anything about scar revision but she said its very difficult to remove a tumor completely from that area. What are your thoughts?

  6. Jennifer on February 1, 2013 at 3:54 pm

    Our American Bulldog was just diagnosed with a grade II mast cell tumor. The report says the tumor extends to the deep surgical cut margin. It was located on the back of his right rear leg and our vet said he cut all the way to the muscle. Does that mean that it’s in his muscle also? Also on the report it states: “The skin specimen from right caudal thigh contains an infiltrative neoplasm composed of atypical mast cells and eosinophils. Mitotic figures are not seen in 10 HPFs.” what does all this mean? Thank you do much

  7. JD on January 31, 2013 at 12:49 pm

    My dog was diagnosed with mast cell cancer almost 5 years ago. I took her to a new vet for her regular exam and shots. The vet noticed that my dog had a small lump on her belly about the size of a nickel. I didn’t want it biopsied because I knew I couldn’t afford to have it treated and besides, she’d had the lump for about 2 – 3 years already and it really hadn’t changed much since I first noticed it. Well, the vet went ahead and stuck a needle in it anyway and then charged me 89 bucks for the test… well within 2 months of that test the tumor had grown to the size of a small orange, and was softball sized within the next 18 months. I was a little more financially stable by this time, so I had the tumor removed, but I still unable to afford ‘treatment’. I’ve been giving her 100 mg Benadryl daily for about 5 years. We are now 7 – 8 years post initial tumor, 5 years post dx. She has several more small tumors and lymph nodes are all enlarged, but she is fat and happy. She eats, has full bowel and bladder control, runs, plays and enjoys her life. She is now 13 and is almost at her life expectancy. I am not so sure that all this treatment for cancer is necessary or beneficial. I am glad I never subjected her to the Side effects of chemo. I think that the assault to the tumor during the biopsy sped its growth. The vet initially told me my dog would die within 2 years w/o treatment… that was 5 years ago. Could it be that the treatment is worse than the disease?

  8. pam on January 28, 2013 at 10:12 pm

    Our 12 year old Mini Schnauzer was diagnosed with a low grade malignant tumor after many invasive procedures to determine this diagnosis. Long story, but our wonderful Vet, of 30 years, removed a malignant tumor from her armpit and got “clean margins” of 1 millimeter. Another long story short, our home town vet hospital recently sold out to a corporation “VCA” as the original doctors are about to retire. Fortunately, our Dr. is still on the same page as us, and told us “if it were his dog, he would not pursue the radiation therapy” that the VCA corporation suggests.

    I have come to realize that we put our pets through these invasive medical procedures, not for them, but for ourselves!! If our pets (dogs, cats) could talk, and we asked them if they wanted to go through surgeries, do you think they would say YES?? Of course they would not!!!!!!!! Animals instinctively mask pain as a right of survival. They know that they need to be strong to survive!!

    I hope my words will convince pet owner’s to think of their pet’s rather than themselves when it comes to pain and their beloved pet’s tolerance for pain.. they will mask it for you as they love you sooo much!!

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  10. Catherine on August 16, 2012 at 7:49 am

    I have a 11 year old German Shepard mix with mast cell cancer 🙁 she had a tumour on the upside of her index finger removed, it was a nasty surgery. After 5 1/2 weeks the wound is still open and bleeding a little. Is this normal?. Also, we soak her foot in water with a small amount of Epsom salt and then use neosporin and wrap it. My question, is this the correct protocol ?

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