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

Beyond Mast Cell Tumor Grade: Other Prognostic Factors

Updated: October 10th, 2018

In my last blog on mast cell tumor (MCT) grade, I discussed that grade is one of the most important prognostic factors, or predictors, for dogs with MCT. And I also discussed the challenges of using the grade as a predictor: a good percentage of grade 2 MCT behave more aggressively than the rest of grade 2 MCT, and the recent news that the grade from a pathologist might not be reliable. What is a dog Guardian to do?

Well the good news is that there are additional tests besides grade that can help us predict your dog’ outcome.

Mitotic Index

One very important test is the tumor’s mitotic index, which measures how many MCT cells are dividing when the pathologist examines the biopsy under a microscope. Thankfully, this test is now routinely included on the pathology report.

Here’s what the numbers associated with mitotic index mean. In a recent study, it turned out that the higher the mitotic index, the poorer the prognosis.

For example, if the score was over 5 on the mitotic index, the median survival time was only two months, regardless of grade.

If the score was under 5, however, the median survival time was seventy months (over five years), regardless of grade.

So, you see, it is very important to know your dog’s mitotic index for their mast cell tumor. This knowledge can really help your oncologist to plan treatments, and you to understand your dog’s prognosis.

It should be noted that reported cutoffs for these prognoses can vary — from 5 all the way to 10. In the newer 2-tiered system described in this post, the cutoff was 7, not five. I expect that the cutoff will continue to be refined as more studies evaluate mitotic index as it relates to the different grading systems.

MCT Prognostic Panel

There is other prognostic information that can be drawn from a biopsy sample that may be helpful. This is often referred to as the MCT prognostic panel or proliferation panel, and it involves evaluating certain markers related the MCT’s proliferation (how much it multiplies) and how much cell division is happening.

The panel typically measures AgNOR, PCNA, Ki-67, c-Kit, and tests for c-Kit mutation status. This a panel helps me to predict whether the MCT will metastasize in the future, whether chemotherapy is recommended, and what chemotherapy to include in the protocol (based on the c-kit mutation result).

One of the most important numbers in the panel is c-Kit and it’s mutation status. One-third of dogs with MCT have a genetic mutation in the c-Kit gene. When there is a mutation, an enzyme called tyrosine kinase is stuck in the “on” position, leading to uncontrolled growth and survival of these mast cells. Studies have shown the presence of the mutation is a negative predictor, but now there are 2 relatively new chemotherapy drugs that target this mutation. I will discuss the c-kit inhibitors Palladia and Kinavet in a future blog.

Only a handful of laboratories have the special stains and expertise needed to analyze the MCT prognostic markers, so I recommend consulting with your oncologist to see if this information is necessary before adding these expensive tests to the biopsy. I find this panel especially informative for Grade II and grade III tumors.

There are several other prognostic factors for MCT included in the Guide, including rapid growth, size, recurrence and location.

Remember what I said in the 1st blog on MCT: MCT are not one size fits all tumors. Not one test – grade, mitotic index, c-kit mutation, or other prognostic factor – can definitively predict your dog’s outcome. But we can use these to help make good recommendations, so your dog can not only live longer with MCT, but live well.

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  1. Julia on April 22, 2020 at 3:01 pm

    My dog was diagnosed with a Subcutaneous Mast Cell Tumor on the left side of his face very close to his snout. Due to the location of the tumor, surgery has been ruled out. My dog’s oncologist is recommending that we proceed with radiation therapy. I discussed my dog’s options with the oncologist and she says my dog has an 86% chance that the tumor will not reoccur if palliative radiation once a week for 4 weeks. Keep in mind, she also thinks his lymph node might also be involved. His meiotic index was a 3. What are your thoughts on the palliative radiation and the prognosis of my dog?

  2. Sandy Schatzer on May 2, 2019 at 6:12 am

    My golden retriever had a mast cell tumor removed. It was grade 3 and I had the c-kit done. I was told it was pattern 3. How long do you think my dog will live? I do not want to do chemo or radiation.

    • Dog Cancer Vet Team on May 2, 2019 at 8:53 am

      Hi Sandy,

      Thanks for writing. Dr. Sue, a vet oncologist and co-author of the Dog Cancer Survival Guide, wrote an amazing article on Mast Cell Tumor Grades that provides some statistics in estimating survival time. Here’s the link if you’d like to check it out:

      As Dr. D writes in the Dog Cancer Survival Guide, there are a number of things that you can do, besides conventional treatments, to help your dog with cancer– under your vet’s supervision. Nutraceuticals, immune boosters and anti-metastatics, diet, and mind-body strategies. This is what he calls the Full Spectrum Approach to Cancer 🙂

      Life quality is also very important and is something that you should take into consideration 🙂

  3. LYDIA on February 19, 2019 at 8:41 am

    Omg…as I read the article in looking at my boys chart and results from his oncologist. Exactly the steps we took but I didnt know anything about the numbers….gotta ask more. I heard @ new reading system- how a high #2 is considered 3 now. Which is so not good or in my favor….curious on the mitotoc index # & if the tyrosine kinase is “on”?
    Very informative and made easier to understand what /why important and what exactly it means and measures. I REALLY HAT THAT CANCER IS STILL AROUND WHEN THE GOVT HAS THE CURE!… My poor innocent lil boy who I thought i was gonna rescue…really ended up rescuing me!…. HE DESERVES THE BEST HAPPINESS FOR HIS ENDING OF LIFE…

  4. Katherine on September 29, 2013 at 8:32 am

    My boxer has a recurring MCT. She is 8 years old. The tumor is located below her rear hock. It is a grade II with a mitotic index of 0-1. The tumor was removed 9 months ago and due to the location, full clean margins were not possible. The tumor has returned (9months later) but it is very small and the lymph nodes are not involved. Ellie is very happy and seems perfectly sound and healthy. What Treatment should I pursue at this point. I am not inclined to pursue radiation or Chemo. I have read about palladium. I am wondering if surgery alone is an option or if I should watch it for now. Again, with the mitotic index 0-1 the tumor has proved to be very slow growing. I am afraid of the chemo as the efficacy seems to be hit or miss.

    • DrSueCancerVet on September 29, 2013 at 3:20 pm

      Hi Katherine,
      Sorry the tumor has recurred. I would strongly recommend you see a boarde oncologist so he or she can make specific recommendations for Ellie. With recurrence, she should have staging test including an ultrasound to make sure the MCT has not spread. If it has not and the tumor is still small enough for surgery, I would do that, and consider a surgeon who is more likely to get margins around the tumor. If surgery is not an option, chemo can be considered. Palladia is more effective for dogs with the c-kit mutation, so discussed testing for this with the oncologist. There are lots of options for Ellie- good luck!
      All my best, Dr Sue

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