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

The Oncologist’s Perspective on Statistics: Part Three

Updated: October 1st, 2018

As you are likely starting to notice, I have so much to say on cancer. I am breaking up big topics into sections to make them more manageable. This is part 3 on statistics.

As I mentioned in part one, statistics can be very helpful to give you reasonable expectations about your dog’s cancer, but as discussed in part two, statistics can be frustrating when your pet suffers an uncommon side effect or doesn’t live up to the statistics that you are quoted.

In this part, I will review a few of the more common statistical terms you may hear. In the Dog Cancer Survival Guide, I discuss many of these terms for 12 common canine cancers.

In canine cancer, a common term you will hear is the median survival time (MST).  Median survival refers to the time it took for half of the dogs to die in a study.  So by definition, half the dogs lived longer than the median survival. For example, if a study had sixty dogs and the median survival time is twelve months, thirty dogs were still alive at twelve months, and thirty dogs were no longer with us.

But why median and not average (typically reported as the mean survival time)? For an average, add up the total survival times for all sixty dogs in the study, and then divide the result by sixty. While this average might seem like a useful statistic, it may not always be so.

If one dog in the study was an extremely long-term survivor, but most other dogs weren’t, the average survival time might give the impression that most of the dogs in the study lived a very long time. The opposite could also be true: if one dog, sadly, died very early after diagnosis, averaging in his short survival time might give the impression that most of the dogs lived a very short time.  The advantage of using MST is that it is less likely to be skewed by these unusual cases. I cannot stress enough: while it is important to learn the MST for your dog’s cancer, no one is “average” and many dogs have much better outcomes than the median.

Other statistical terms you may come across:

Response rates tell us the percentage of dogs that respond to a particular treatment or protocol. This is a common statistic for chemotherapy protocols. For example, the response rate for canine lymphoma to a multi-agent CHOP protocol is 85 to 90%, but the response rate to a COP protocol is lower, approximately 60 to 70%.

Cancer recurrence is defined as the return of cancer after treatment. For example, the overall recurrence rate for a soft tissue sarcoma after surgery is 15% and usually within one year, but for dogs with soft tissue sarcoma removed with incomplete or dirty margins, the recurrence rate jumps to 30%.

Metastasis rates tell us how likely the cancer is to spread to other parts of the body. These rates help oncologist with treatment recommendations. For example, oral melanomas are not only aggressive in the oral cavity, they metastasize to the local lymph nodes, liver, lungs, and kidneys at rates of greater than 60-80%. Preventing the spread with something like melanoma vaccine is is just as important as treating the tumor in the mouth with surgery and/or radiation. On the other hand, for an oral cancer like a low grade fibrosarcoma, metastatic rates are pretty low, so chemotherapy is not typically part of the treatment plan after surgery and/or radiation.

So hopefully, understanding the usefulness and limitations of statistics will help you understand the options and recommendations for your dog. I also remind you that worrying over your dog’s outcome – whether he will live up to or exceed statistics – will not change the outcome. It is wasted energy. Instead, I recommend you focus on caring for your dog through his treatment, giving medications and supplements, and giving your vet feedback on how your dog is doing at home. And most importantly, enjoy each and every day you share together. That is where energy should be focused.

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  1. How long will my dog live? | MoseyLove on August 1, 2018 at 11:11 am

    […] and statistics related to a cancer. I’ve discussed some of the common terms in a previous post, The Oncologist’s Perspective on Statistics: Part Three. In that post I discuss median survival times, response rates, metastasis rates. These are […]

  2. Ms. Charlie W. on November 13, 2012 at 1:28 pm

    Dr. Dressler, I was researching the type of cancer my precious dog, Dude, was diagnosed with, the soft tissue Fibrosarcomas oral cancer on the upper jaw. The suggested treatment is doxorubicin chemo 1 tx so far with piroxicam then Palliative radiation therapy (six treatments- he is on his 3rd tx) then return to doxorubicin.

    Eight days after the chemo (also started piroxicam at least a week before the chemo) Dude got very very ill with severe diarrhea and extreme lethargy and just wanted to lay as far away from the house in theback yard as possible. I had to carry him into the house. He was given medicine for diarrhea but the oncologist wasn’t sure why he got so sick 8 days after chemo. They didn’t believe it was the chemo and thought it might be the piroxicam. My fear is whatever it was nearly killed him so I’m hesitant to return to the chemo with piroxicam.

    What has been your experience with the above treatment and side effect?

    I was reading a book “Cancer and your pet” by Debra Eldredge and Margaret Bonham and they reported some positive outcomes combining chemo with NSAIS’s and were so excited about great outcomes with bladder cancer and developed a new and relatively safe treatment for dogs and tried in on canine oral cancers that can’t be operated on.

    This book was dated 2005 is there more current research on this? What are more current outcomes? Also Can’t my dogs tumor be removed with surgery even if it means removing the upper jaw bone? Nobody seems to think so.

    Dude is 12 years old and show no signs of illness, he is my best friend ever and he just loves me and I him, he is the best dog ever, so I want to leave no stone unturned in finding the best possible chance of him beating this cancer!

    Your feedback would be invaluable.

    Ms. Charlie W.

  3. Melody Sandberg on March 15, 2012 at 12:21 am

    Hi – I hope you will address this question for me. My vet is also researching this because at this point he doesn’t know the answer. My 5# Yorkshire Terrier 13.5 years old has been diagnosed a a Type A Melanoma. My vet has removed the mass as well as he could and had it biopsied (sp?). He said he felt very good about the normal Oral Melanoma being treated with the Vaccine, but was unfamiliar with this Type A Melanoma. Scooby Doo (my Yorkie) is on your Apocaps as well as home made diet and K9 Immunity +. He will be getting put on the Doxycycline today. Please advise if you have any experience with the Type A Oral Melanoma and if it reacts well to the Vaccine? Per my vet, the type A does not have pigmentation. Thanks is advance for any expertise you can contribute. Cordially Melody A. Sandberg, Guardian

  4. Mary Emmons on February 22, 2012 at 1:14 pm

    Thanks. . I love the last part where you mentioned worrying about your dogs outcome is wasted energy. We can only do the best we can to help them stay healthyl, happy, and enjoying their lives right now. If my best friend lasts even longer than statistics that will be a bonus!

    • Dr. Susan Ettinger on February 24, 2012 at 1:25 pm

      Thanks Mary! Positive energy goes a long way!
      All my best, Dr Sue

  5. Jeannette Botza on February 22, 2012 at 8:53 am

    I have just recently lost my beautiful little girl after 12years from Hemangiosarcoma. I did everything possible to keep her as long as I could, but
    lost her after 6 months. My question now is I will be getting another dog soon,
    as my heart is so empty. WHAT ARE YOUR RECOMMENDATIONS ON
    VACCINATIONS??? I have read Dr. Dressler’s book and have had
    long distance advice with him for my little one that died. What vaccinations
    should I give and I often. She is 8 months old and has only had a parvo
    vaccination. Please help….

    • Dr. Demian Dressler on February 28, 2012 at 4:26 pm

      Dear Jeannette,
      my advice is to start the vaccine series later (at 8-10 wks of age) and give them once monthly until after 16 weeks, then at 1 year, 4 years, and 7 years, then stop. This does not mean we only go to the vet every 3 years- still go at least annually and twice yearly after 7 years of age. There is a section on cancer prevention in the back of the Guide that may interest you.
      All my best,
      Dr D

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