How to Use the Mitotic Index to Make Decisions About Mast Cell Tumors
Dr. Demian Dressler is internationally recognized as “the dog cancer vet” because of his innovations in the field of dog cancer management, and the popularity of his blog here at Dog Cancer Blog. The owner of South Shore Veterinary Care, a full-service veterinary hospital in Maui, Hawaii, Dr. Dressler studied Animal Physiology and received a Bachelor of Science degree from the University of California at Davis before earning his Doctorate in Veterinary Medicine from Cornell University. After practicing at Killewald Animal Hospital in Amherst, New York, he returned to his home state, Hawaii, to practice at the East Honolulu Pet Hospital before heading home to Maui to open his own hospital. Dr. Dressler consults both dog lovers and veterinary professionals, and is sought after as a speaker on topics ranging from the links between lifestyle choices and disease, nutrition and cancer, and animal ethics. His television appearances include “Ask the Vet” segments on local news programs. He is the author of The Dog Cancer Survival Guide: Full Spectrum Treatments to Optimize Your Dog’s Life Quality and Longevity. He is a member of the American Veterinary Medical Association, the Hawaii Veterinary Medical Association, the American Association of Avian Veterinarians, the National Animal Supplement Council and CORE (Comparative Orthopedic Research Evaluation). He is also an advisory board member for Pacific Primate Sanctuary.
Updated: April 13th, 2021
Summary
Is using the mitotic index mast cell tumor diagnosis useful? In some cases, not as much as others. But when it’s useful, it’s REALLY useful!
There is a lot of uncertainty in canine cancer, and mast cell tumors are the tumor type that proves it. Mast cell tumors are tricksters, with seemingly benign tumors sometimes turning out to be very aggressive … and often enough to be confusing, vice versa. When we’re talking mast cell tumors, we are definitely in what I call “the gray zone.” Determining just how aggressive the tumor is up front is important when it comes to making treatment decisions, which is why Dr. Ettinger, my oncologist co-author, suggests looking at the mitotic index for mast cell tumor assessment.
The most common instance of confusion in mast cell tumor diagnosis is for the grade 2 mast cell tumor. As you may already know, the “grade” is a measure of how aggressive a cancer is. When we say a cancer is a “high grade malignancy” we mean it is hard to cure. A “low grade” growth is easier to cure as a generality (but not always), usually by surgical removal.
Grading Mast Cell Tumors
In mast cell tumors, the grade is usually broken down into three levels, with grade 1 being the lowest and grade 3 being the highest and most aggressive. (There is also a newer, 2-tiered system of grading mast cell tumors that may be available to your oncologist and may be useful in real “gray zone” cases.)
So, if your dog has a grade 3 mast cell tumor, it’s considered aggressive cancer. Aggressive cancers do things like regrow in the same spot even after surgery (recur) or spread to surrounding areas (local invasion). Aggressive cancers can also spread to distant sites … places like the spleen, liver, bone marrow, or other remote areas, which is called metastasis.
If your dog has a grade 1 mast cell tumor, thankfully, it’s considered less aggressive. This means that it is likely going to be cured with a surgery with wide margins that gets the whole tumor out. This doesn’t mean that grade 1 is ALWAYS cured with a surgery — just that it is more likely to. And make sure you ask for wide margins!
Grade 2 mast cell tumors are intermediate, by definition, and highly unpredictable. These are the tumors that earn mast cell tumors their nickname “the trickster.” Grade 2 mast cell tumors can behave aggressively (like grade 3’s) or more like benign growths (grade 1’s).
It’s grade 2 mast cell tumors that can most benefit from a mitotic index measurement. The number will be on your biopsy report.
Get the Biopsy!
You will not know the grade of your dog’s mast cell tumor until after the biopsy is performed, of course, so you can’t use the mitotic index for mast cell tumor assessment until AFTER you get that tumor surgically removed (with wide margins, please!).
If you are looking at a grade 1, the likelihood that your dog will need more treatment is low. For a grade 3 tumor, which is seriously aggressive, you are almost certainly going to get more treatment recommendations. But what about that gray zone, the grade 2 mast cell tumor?
There are a couple of ways to treat a grade 2 mast cell tumor. You could do a second excision (surgery) with wider margins. You could add chemotherapy and/or Palladia to your treatment plan. But which action plan to take is in the gray zone until another bit of information:
Mitosis
Mitosis is a part of cell division, the way that cells replicate themselves. You can actually see mitosis happening in cells under a microscope. It looks something like this.
Public Commons Image https://commons.wikimedia.org/wiki/File:Major_events_in_mitosis.svg
To get the mitotic index, the pathologist looks at a slide with a very thin slice of your dog’s tumor tissue on it. The tissue has been stained so it is colored and they can easily see which cells are dividing (in mitosis). They simply count the numbers of these cells to get the mitotic index. The higher the number, the higher the mitotic index and the more aggressive the tumor.
If you think about it, this will make sense. The more cancer cells divide, the faster they replicate themselves, the bigger the tumor, and the bigger the problem for your dog. More cell division, faster growth, higher mitotic index.
Mitotic Index Mast Cell Tumor
So what does the mitotic index actually mean for mast cell tumors?
Well, generally, a lower mitotic index is better. Fewer dividing cells = a less aggressive cancer.
For grade 2 mast cell tumors, the magical number to hope for is a mitotic index of 5 or less. These dogs, with conventional care alone, have a median survival time of 70 months, or nearly six years. That’s a nice long median survival time.
Unfortunately, dogs with grade 2 mast cell tumors with a mitotic index of greater than 5 have a dramatically shorter median life expectancy of only 5 months. This is quite a dramatic difference.
Here is the abstract to show you where I am getting this information.
Bottom Line: How to Use the Mitotic Index for Mast Cell Tumor
Again, you might not really need to consider the mitotic index if you get a grade 1 or 3 tumor. In those cases, your direction will be more clear-cut.
But in cases where we have a grade 2 mast cell tumor, the mitotic index (MI) can help you make decisions about what to do next.
If you have a grade 2 mast cell tumor with a mitotic index of <5, your minimum treatment surgery with a wide excision of 2 to 3 centimeters. If you have that already, you might not need any more treatments, but your oncologist might want to use other steps, including chemo and/or radiation. With a median survival time of 70 months, taking those extra steps might not feel necessary in every case. (Remember, I don’t make direct advice over the internet, because every case is different. I’m not saying that you should not get extra treatment if your dog’s MI is under 5. I’m just saying in general, they may not be as necessary.)
But in cases where we are looking at grade 2 mast cell tumors with a mitotic index of >5, these cancers should be considered very, very dangerous and aggressive. If your dog is young, and you would expect her to live a long time if she weren’t sick, you might be more aggressive with the treatments than you would if the MI were <5. I would certainly consider chemo and radiation with your oncologist. If your dog is close to or beyond his average life expectancy, I would suggest it is time for ethical considerations and maybe a focus on life quality enhancement.
Regardless of the grade of tumor or the mitotic index, your dog will benefit from the dog cancer diet, supplements, life quality enrichment, and the other complementary aspects of care Dr. Ettinger and I cover in detail in our book The Dog Cancer Survival Guide.
Best,
Dr D
Dr. Demian Dressler is internationally recognized as “the dog cancer vet” because of his innovations in the field of dog cancer management, and the popularity of his blog here at Dog Cancer Blog. The owner of South Shore Veterinary Care, a full-service veterinary hospital in Maui, Hawaii, Dr. Dressler studied Animal Physiology and received a Bachelor of Science degree from the University of California at Davis before earning his Doctorate in Veterinary Medicine from Cornell University. After practicing at Killewald Animal Hospital in Amherst, New York, he returned to his home state, Hawaii, to practice at the East Honolulu Pet Hospital before heading home to Maui to open his own hospital. Dr. Dressler consults both dog lovers and veterinary professionals, and is sought after as a speaker on topics ranging from the links between lifestyle choices and disease, nutrition and cancer, and animal ethics. His television appearances include “Ask the Vet” segments on local news programs. He is the author of The Dog Cancer Survival Guide: Full Spectrum Treatments to Optimize Your Dog’s Life Quality and Longevity. He is a member of the American Veterinary Medical Association, the Hawaii Veterinary Medical Association, the American Association of Avian Veterinarians, the National Animal Supplement Council and CORE (Comparative Orthopedic Research Evaluation). He is also an advisory board member for Pacific Primate Sanctuary.
Hi, I am so confused of what to do for my thirteen and a half Shit Tzu dog. Last November he had removal of Two large mast tumors low grade 2. Two months ago I felt two more and they grew very quickly. He had surgery June 21, 2019 and his stiches removed week after. The biopsy shows progression. I went to see an oncologist and they found 2 more aggressive mast tumors. I found two more lumps by his stiches. My Vet and the oncologist suggest Palladia treatment. I know every dog is different but I am afraid of the side affect and the quality of life for him. My family and friends think that I should let him be. Can you please give me your sugestions. My email is zahtilag@gmail. com Thank you so much
In January, my dog had a mast cell tumor removed from the top of her paw, near her toes. It was a low grade 2.
One week ago, she had another mast cell tumor removed from the same area, and she also had two digits removed. The tumor came back as a stage 3 with a mitotic index of 100. My oncologist recommended chemo.
I am uncertain as to how to proceed. All of the literature that I find says that her life expectancy is about two months with such a serious tumor (although I can’t find any literature addressing a mitotic value that is so exceedingly high).
Do you have any advice for me? I am so heartbroken.
Hi Carisa, thank you so much for your comment. We’re not veterinarians, so we can’t offer medical advice, but it’s a good idea to make a list of questions for your oncologist so you can make this decision. Ask questions like “how much time do you think we have if we don’t treat?” and “how much time will chemo gain us?” And keep in mind that no one has a crystal ball, so nothing is guaranteed 🙁 You should also try addressing all the other things that can be done: nutraceuticals, anti-metastatic supplements, diet changes, and mind-body strategies: https://www.dogcancerblog.com/articles/book-excerpt/cancer-treatment-for-dogs/
In the end, cancer is just totally heartbreaking, as you’ve discovered. So while you’re taking care of your dog, please remember to take care of yourself, too, and first. The first section of The Dog Cancer Survival Guide has lots of coping strategies that can really help. https://dogcancerblog.com/book. And don’t forget to reach out for support. If you have a copy of the book, you can join our private “book club” support group on Facebook, for example. It’s super helpful! https://www.facebook.com/groups/dogcancersupport/
Much Aloha, Molly
What is a mitotic index of 31/10?
Hi Brett! We’re not veterinarians (or pathologists 🙂 here in customer support, so we can’t say for certain, but we assume that what those numbers mean is that when the pathologist examined the tissue, they used a 10X power field of view — that’s the 10 — and counted 31 cells undergoing mitosis. So your mitotic number is 31, which is certainly greater than 5. However, the best way to get this answered is to ask your own vet to tell you what that /10 part of the number means. They will be able to tell you for sure, either by phone or email.
Hi there,
i found this after trying to figure out what to do for my Pittie. He was diag with Mast Cell Tumor Stage 2 but with a high mitotic index of 52. It was in his nail bed where the tumor started and his toe was amputated, we recently found that it has gone into the lymph node. The next step is for an ultrasound to see if it has spread to his organs which is $900. They then want to start Chemo. My question is with his Mitotic so high and in his lymoh node we are not being told what his life expectancy is if we just keep him comfortable for now or will chemo even give us any time like 3 years. Please help as we have already paid 2,100 and no treatment has been started.
Hi Katy,
Thanks for writing! We’re not veterinarians here in customer support so we can’t offer medical advice. However, we can provide you with information based on Dr. Dressler’s writing
Deciding on a treatment plan for your dog is one of the hardest choices you have to make as there are so many things to take into consideration (finances, your dog’s personality, your personality, treatment options, age, etc), and there really is no one right fit because each dog and their situation is unique. This is where Treatment Plan Analysis can be really beneficial. Here’s an article on how to end treatment plan analysis paralysis that you may find useful : https://www.dogcancerblog.com/blog/make-decisions-dog-cancer-treatments/
You also have to factor in your guardian type– do you want your dog to be as comfortable as possible? Are you okay with handling the side effects of particular treatments? How important is quality of life? Here’s a link to an article on this topic that you may find beneficial: https://www.dogcancerblog.com/blog/why-your-personality-is-so-important-to-your-dog-with-cancer/
You know yourself, and your boy the best, so once you figure out what is most important to you, and take all of those factors into considerations, you can then decide on a treatment plan for your boy In the meantime, as Dr. D writes in the article above, you can make changes to your dog’s diet, and implement life quality strategies.
We hope this helps! 🙂
I believe there is a typo in the following paragraph; I believe you meant to write MI >5, NOT <5, since this conflicts with the previous paragraph stating a MI<5 is not as aggressive.
"But in cases where we are looking at grade 2 mast cell tumors with a mitotic index of <5, these cancers should be considered very, very dangerous and aggressive. If your dog is young, and you would expect her to live a long time if she weren’t sick, you might be more aggressive with the treatments than you would if the MI were <5. I would certainly consider chemo and radiation with your oncologist. If your dog is close to or beyond his average life expectancy, I would suggest it is time for ethical considerations and maybe a focus on life quality enhancement."
I believe there is a typo in the following paragraph; I believe you meant to write MI >5, NOT <5, since this conflicts with the previous paragraph stating a MI<5 is not as aggressive.
"But in cases where we are looking at grade 2 mast cell tumors with a mitotic index of <5, these cancers should be considered very, very dangerous and aggressive. If your dog is young, and you would expect her to live a long time if she weren’t sick, you might be more aggressive with the treatments than you would if the MI were <5. I would certainly consider chemo and radiation with your oncologist. If your dog is close to or beyond his average life expectancy, I would suggest it is time for ethical considerations and maybe a focus on life quality enhancement."
Noted and fixed. Thank you!
The “grey area” is particularly vexing us. Our 3 1/2 year old yellow lab had a mast cell tumor removed from her paw. it is healing and the surgeon said he got good margins. He also removed a lymph node right behind her knee which had a very few cancer cells. They are calling it a Grade 2 high grade tumor but the mitotic index is 1. The Oncologist is suggesting a series of 8 chemo shots. We are almost ready to go with this, but this low mitotic index makes us believe she might be fine for a number of years without chemo. Any thoughts would be appreciated.
I do hope this entire blog posting will be made available to help others. We lost our beloved BRT yesterday afternoon to adenocarcinoma. We have responsibly loved and owned dogs and horses for over 40 years. She was 9 years and 8 months old. Average life expectancy is 12-14 years. She was always well cared for as a retired AKC champion and family member. Our hope is that this information will help others faced with mammary tumors in beloved canine soul mates.
History She had a small mammary growth removed about 2 years ago – the vet gave us the choice of a biopsy which we declined. Never, ever decline a biopsy – a good vet will demand that a biopsy is performed! Two weeks ago, we notice a reddened, inflamed mammary gland and visited our routine vet the next morning. This is the synopsis of a horrific series of events:
1. Detected mammary mass and immediately visited our local vet
2. Large mass examined, measured, and 10 day course of antibiotics prescribed (cephalexin1000mg twice daily) and a herbal alternative to boost immunity. MISTAKE #1 – at this point I should have secured a second opinion by an oncologist.
3. No initial needle aspiration or biopsy under sedation was offered or performed
4. No chest films offered or performed
5. No improvement of inflammation and getting bigger at 10 days. Returned to vet and agreed to have the mass surgically removed, biopsied, and adjacent lymph node biopsied.
MISTAKE #2 We should have second opinion specialty care before any surgery performed.
6. Agreed to have herbally derived preparation that generates apoptosis in cancer cells applied around excised margins during surgery as discussed with vet. MISTAKE #3 – should have obtained second opinion from oncologist.
7. Brought our angel home next day with dozens of staples, drain tubes, more cephalexin and tramadol for pain. E-collar, confined to our bedroom, no mobilization except potty break. Basically had a bi radical mastectomy with three glands and lymph node removed.
8. Less than 36 hours later noticed a couple of staples open – called and was instructed to treat with raw honey compress and bring her back in a couple of days. Picked up more tramadol for pain at clinic. Later that evening, more staples began to open in her groin area. Given same care instruction for the new area. During the next 24 hours her entire abdominal area opened little by little. We took her to an emergency clinic at 9:30pm that same night thanks to the quick insistence of her breeder who was here for a visit helping me change her bandaging. Our angel endured another prolonged surgical procedure to clean out the infected, now totally open, surgical wound in an attempt to save her life. It was a long night at the emergency clinic. Baytril, Clavamox, and metacam for pain given to her at discharge. Only then was I given a pragmatic picture from ER vet about the gravity of this infection and the care that would be required for her to have a chance to survive and heal.
9. As follow up to ER clinic instruction, the next morning we took her to a highly recommended clinic that is vet to friends of our breeder. All records transferred to new practice with extensive experience in open wound care and cancer treatment. They agreed to admit her to conduct emergency wound care. Less than 24 hours after the emergency clinic visit, our sweet girl underwent a third surgical procedure to effectively and skillfully clean up and treat the putrid surgical wound to prepare for healing from the inside out with what we all believed was a good prognosis for recovery.
10. Histopathology report 5 days after surgery and biopsy sent to specialty vet from local vet. Results showed stage 3 adenocarcinoma, lymphatic and vascular involvement with a high mitotic index. She should never have had any surgical intervention much less one that was so extensive.
Heart breaking, we said goodbye to her yesterday afternoon. In her stoic and loving Black Russian Terrier nature her tail was wagging as I lay beside her and gave her all she would eat – her favorite treat of baby carrots. She is always with us and I hope we have helped guide you in a more informed direction if you should have to address this serious health issue.
Oh, My, God… I would be furious. and totally heartbroken! I’m reading this article because of my dog with MCT, and happened upon your comment and it just breaks my heart!! I am so sorry you had to go through that. I hope that the vet who performed that surgery has been held to account.. no one should ever have to go through something like that.
Oh Carolyn these are the questions for which there is no definite answer. Could it all be gone? Yes! Should you let your guard down? I never do. Always stay vigilat. If cancer has once been present I think of it as an invading army inside my fenceline. I can purge the army, but I’m not going to switch off the alarm system if one crazy soldier could still be hiding. Celebrate the joy and have fun with your dog! That’s it’s own medicine. What a wonderful, clever girl to have done so well with the surgery. And she’s feeling your relief too. Keep up wonderful nutrition, limit exposure to carcinogens and cheap treats, and keep up the vet checks. Ask your vet what you might need to watch for, then just make it a task without the worry. Play every day and cuddle every day. Trade your worry for awareness and live in the moment with your girl. Good luck!
My 14 year old Jack Russell was just diagnosed with a grade 2 mct a month ago. It was removed over a week ago. It was cutaneous and my vet did a very large scale removal it looks like. The lab results show the grade 2 mct has a mitotic index of 13. It also showed the neoplasm completely abuts the layer of panniculus muscle. Of course I am copying this from the lab report because I had no idea until today what any of those words mean. My question is this…could all of it be gone, and no further worries? She’s acting very happy and perky. Just like normal. No lethargy, healthy appetite, etc. Because she is acting so healthy and happy, could that mean she is perfectly fine? If it had mestastisized (sp?) to other areas, wouldn’t she be showing some distress?