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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

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  1. results for MCT & FNAs « g a l o d y on February 8, 2012 at 12:38 pm

    […] about the ‘mitotic index’ and why it is important for prognosis can be found here, on the Dog Cancer Blog.  I can now perhaps stop beating myself up for not acting […]

  2. Julia on June 8, 2011 at 1:38 pm

    Hi Dr. Dressler,

    My 8 1/2 year old mixed breed dog had a stage 2 mast cell tumor removed from his hind leg about two months ago. The incision site took several weeks to heal; it kept ripping open and having to be re-stitched. The lab said the removal had incomplete margins. My vet sent me to an oncologist and we had a tumor marker test done that came back with a 65 reading (I’m not sure what this means exactly, but apparently over 54 is likely to metastasize). The oncologist is recommending localized radiation as well as chemotherapy asap.

    I’m not sure yet what myself, my wallet, and most importantly my dog can handle. While I understand nothing is 100%, I am trying to weigh the potential of a successful outcome with the negatives.

    What I cannot seem to understand is this: Since the radiation will have been delayed so long due to the difficult healing, is it still nearly as effective?
    Also, how much should I take the tumor marker results to heart?

    Thank you for any input in this confusing time,

  3. Clarissa S on May 23, 2011 at 9:32 am

    Dear Dr. D,
    I have a 4 year old Boston that just recently had two mast cell tumors removed from his hind leg. They were fairly small and close to each other so only one incision. One of the tumors came back after biopsy as a Grade I, the other was diagnosed as a Grade 2. In reading the reports of the biopsy, the findings say similar things for both “Nulcie are pleomorphic with scattered chromatin and a low (<1 mitotic figure per 10 hpf) mitotic index". The comments on the Grade 2 tumor are more extensive. I'm wondering is it possible for a Grade 1 and 2 tumor to have similar mitotic figures? The recommendation from my vet was to see an oncologist. Should I have cause for concern?

    • DemianDressler on May 25, 2011 at 9:01 pm

      Dear Clarrisa,
      i too would see an oncologist, especially if your vet is recommending it. This tells you that your vet is suggesting more expert advice, and if your vet is telling you this, I feel it is sensible wisdom. There are more aspects of a pathology report than mitotic figures, and there are other determinants of tumor behavior as well. However, right off the bat, I have cautious optimism that things will be okay. But it is important to follow your vet’s advice. I hope you are also using the other steps to help your dog? Diet, apoptogens, immune support, and the rest of the steps in the Guide??
      Dr D

  4. Jenifer McClellan on May 16, 2011 at 3:42 am

    Dear Dr. Dressler:

    I recently adopted a 7 year old rescue dog (Wiemeraner/Lab mix) with Diabetes and Thyroid Desease, both are now under control with proper exercise and diet and medication. I discovered a swelling on her front leg and a smaller swelling on the back thigh, they looked completely different from each other. I took her to my vet, he said it wasn’t swollen and no idea what it was. A few weeks later it happened again in both area’s and I took her to another vet who said they were Mast Cell tumors. I called the rescue group and found she had a grade 2 tumor removed 8 month’s ago on the front leg and this was a recurrence, and another removed from her belly which now has also recurred plus the new one on her thigh, and since have found numerous more small ones. I had some asperated and 1 out of 3 came back positive, so my vet sent me to an Oncologist. The Oncolgist has diagnosed her with Cutaneous Mastocytosis and said she has 3 to 6 months to live. She does not recommend surgery as there are so many tumors and the larger recurrence on her front leg removed last year and could only get 1mm margins (clean) but there is not enough tissue to work with and the muscle would be very damaged trying to remove it again, the leg would be useless. So Chemo has been recommended 8 treatments and then inhibtors there after. My question is, is this a reasonable thing to do for her. She is not in pain, has been on Benedryl and Pepcid 2 weeks now (ordered by our vet) but with her Diabetes and other heath issues I am unsure of what is the best course of action for her??? Any advice would be appreciated. Jen

    • DemianDressler on May 18, 2011 at 8:53 pm

      Dear Jennifer,
      you need to do a treatment plan analysis as is discussed in the Guide. Get an idea of side effect frequency, side effect severity, what the life quality negatives are with treatment, what are the odds of a response given the recommended treatment, and what is the added life expectancy (median, like an average) with the treatment. Once you obtain this specific information from your oncologist your decision will clarify.
      Dr D

  5. jess on May 4, 2011 at 8:19 pm

    Dear Dr. Dressler:

    I have written to you before and purchased your book and have read everything I could possibly find on mass cell. My Boxer Scarlet is currently on CEENU (Lomustine) she was on the protocol vanbalastin before but, the cancer started growing again and their is lympe involvement, Palladia was considered but, the Ceenu seemed to have the best trials. The tumor looks as if it has stayed the same size on the surface but, the last X-Rays showed it had gone deeper. Is compassionate program with Dr. Albert Ahn regarding the drug Masitinib an option if my oncologist request it. Scarlet also on predisone, benedry and Cimetidine, Apocaps. We also have her on Reishi mushrooms. My Oncologist is aware of all we are giving her and has been as helpful as she can be. She is not a canidate for surgury and is stage 3 mct.
    We, are trying to prolong her life and her comfort but, we are getting short of funds and I want to have an answer if this drug must be stopped because it has stopped working. I want her to be well, but I know I must do what right for her. I have noticed in the last day or so that her breathing has been more labored but, it hard to tell if the predisone side effects or it’s because the lymp mass cell has gone deeper. I am taking her to my vet tomorrow – I look forward to your response and appreciate any advice you could give.


    • DemianDressler on May 18, 2011 at 9:05 pm

      Dear Jess,
      Sorry to hear this- sounds very hard.
      if the drug is not working discuss discontinuing it with your oncologist. You might also consider Neoplasene at this stage. I hope this helps,
      Dr D

  6. Cristina on March 14, 2011 at 3:16 am

    Hello Dr. Dressler,
    my dog American Staffordshire Terrier 6 year old has a mast cell tumor on the hind leg, just above the hock. Current size 3cm x 4 cm.
    It is became visible as an insect bite at the beginning of December, believing that I was not worried. As a result of having grown up in January I brought him to my vet. After a week of antibiotic has been done fine-needle aspiration and further the tumor is ulcerated, swollen and raised. 1 week after the analysis has formed another small nodule (3-4 mm) and analyzed by our oncologist considered as “compatible with metastases”. It could have been formed because of fine-needle aspiration.
    Oncologist said me: first staging, afer surgery.
    We have completed staging: chest x-ray, abdominal ultrasound with fine needle aspiration liver and spleen, there are no metastases and all analysis are normal. Prednisone caused diarrhea by a week. Now, the oncologist, becouse of the second nodule, want to do a cycle of chemotherapy (2 or 4 therapy sessions) – for cytoreduction and operating margins as clean as possible – before surgery.
    Personally, this change of direction gave birth in my mind to many questions about how to intervene, especially as it is not certain that the chemo ensure what the doctor is hoping (clean margins). Like any pet-owner I want give him the best, Can you let me know your approach in similar situations to evaluate other opportunities to better treat my dog. Sorry for my english..
    Thanking you in advance, best regards

    • DemianDressler on March 19, 2011 at 5:20 pm

      Dear Christina,
      as far as conventional oncology goes, this plan sounds very much according to standards. Don’t forget the diet, supplements (apocaps, omega-3, K-9 immunity, artemisinin, etc) discussed in the Guide.
      If surgery is not an option, one could consider Neoplasene, but be prepared to deal with an open wound for what may be a long time. Hopefully famotidine and benadryl are being used too..
      Of course, be sure to make any changes with veterinary supervision.
      Dr D

  7. Jen on February 12, 2011 at 10:58 am

    Hello Dr. Dressler,

    I wanted to follow up on an earlier post. I have heard about mast cell stabilizers used successfully in humans and, through a search, found this thread and an earlier question about whether these could be used to treat canine MCT. My 11-year old Lab has had 8 MCTs removed over the past 8 years – all grade 2 (so, about 1 surgery per year). He’s been through a lot of surgeries. He’s getting older and doesn’t bounce back quite as well from them now.

    I would love to find something that may have a chance of preventing tumor growth. Do you see any potential for mast cell stabilizers, such as Ketotifen? Or, maybe quercetin would have a similar effect. Have there been any studies on this to your knowledge?

    Thank you in advance for any comments or insight you could offer.

  8. Jeannine Sovet on January 22, 2011 at 9:02 am

    Dear Dr. Dressler,
    My 12 yo Bichon Stella was diagnosed with Mast cell on her (L) hind leg in Aug. 20, 2010. She had a wide margin excision on 09/2/10 which came back as grade III with dirty margins and lymph node involvement. I found your website and ordered your survival guide. I started her on your cancer diet right away. I also started her on K9 immunity plus, milk thistle, a multivitamin, benedryl(25mg) tid, Cimetidine(200gm) bid , and 1000mg fish oil tid. I got her into an oncologist and he started her on masitinib on 9/23/10. Her tumor was already starting to grow back at this time. Two weeks after starting her on Masitinib her enzyme levels in her liver started to elevate so we discontinued treatment and the following week when I took her in to see the oncologist we started her on the triamcinolone injections which she has been getting every two weeks since then. Now it Jan.22, 2011 and it looks like the injections may not be working anymore.. Twelve days from her last injection her tumor grew so large and looked so mean and she was in pain and I thought it was going to burst so I rushed her to the vets… The oncologist said we would probably have to start thinking about what are next options are for my little girl… The injection brought it down to about 50% it usually brings it down 75%. It still looks very angry but it is not bothering her at all, but now she has blood in her feces (which she never had before). She is still a very happy, energetic dog, still full of life and still getting into trouble(Stella’s usual). I’m scrapping the bottom of the barrel to pay for her vet bills. Is their anything else you can recommend we try. If the injections are not going to work to keep her tumor at bay and it gets any bigger then it did the last time I fear I will have to put her down due to the pain it is causing her.( it doesn’t seem to bother her at all when it The thought that I will have to put her down while she still has so much life in her just kills me. I would do anything for my little girl but i will not let her suffer in pain… Please Help..

    Jeannine and Stella

  9. Renee on December 28, 2010 at 5:52 am

    Hi Dr. D.
    I have a 10 yr old Lab/sheppard mix girl named Almond! She had surgery 12/6/10 to remove a mast cell tumor. Results came back as a Grade 2 with clean margins and her mitotic index was low like 1 (cant remember the wording). I brought her last week to an oncologist and now Im so confused on what to do. The doctor said that there is alot of positives on my baby’s side. But the only thing was the size that she questions. The size was alittle under the size of a nickel. It would go down and come back but never got bigger. I had noticed it in August,2010 and the vet at the time said to watch it. Not knowing that the fact that it was getting smaller and coming back was a sign. I thought if it got bigger than to worry! Anyway the problem I have now is deciding on what to do. She said I could wait and see just keep having her checked or I could do Chemo & the drug Palladia. Can you please advise what you think? Im so scared to make the wrong decision. If I do the drugs she could have a side effect and if I dont she could have the cancer spread. She says her chances without Chemo are 70% and with 90% but there is a 10% side effect with the drugs. Please help me! I want to do the best for my dog! I Love her sooo much! Thank you in advance!

    • DemianDressler on December 29, 2010 at 11:16 am

      Dear Renee,
      This is a great question for a blog post. I will answer in the next general post!
      Dr D

  10. Deborah on December 10, 2010 at 8:57 am

    Hi Dr. Dressler, We found out two days ago our 2yr old female boxer “Roxy” has MCT. She had 4 lumps that I saw so I took her to the vet. One on her nipple two on her neck and one on her rt hip they looked pretty small.The vet wanted to do surg asap so the nexxt morning she went in. The ultrasound was negitive. When Roxy was in surg. the vet discovered one more lump on her ear and removed it as well. All 5 are MCT. The vet said they look like 2or3’s. Roxy is so young what are the chances of her getting more of these or it matasticing? Please help me understand this?. Thanks Debbi

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