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

Using Dog Cancer Statistics

Updated: October 11th, 2018

The one of the first steps in the plan for helping you with dog cancer in The Guide is data collection.  Without data about your dog’s cancer, survival times, life quality during treatment, side effects, costs, nursing care you will be expected to do, your dog’s normal life expectancy and so on, you will be lost.

Let’s look at a central statistic used in discussing dog cancer treatment plans: survival time. Whether you decide on chemotherapy, radiation, surgery, diet, supplements, touch therapies, stress reduction in your dog or any of the different aspects of care, you will want to keep survival time in mind.

The two benefits of treating a dog with cancer are added longevity (increases in life time), and added net life quality (any negatives from treatment are outweighed by the overall increase in good life quality from the treatment).

Survival time is very important.  For many, it is even more important than life quality.  For many, it is less important.  Regardless, it is a big item in any consideration.

So we look at what may be called life expectancy gain.  This is just the difference in life span gained with treatment, compared to that without treatment.

You would ask your vet or oncologist this central question:

“In your opinion (and I will not hold you to this as I understand every dog is different), what is an educated guess on how long my dog has if we don’t use these treatments compared to how long my dog has if we do use these treatments?  What is the payoff in terms of life extension?”

Notice we are using the phrase, “educated guess.” Why is this? The reason is because even if we have references, published data, the number used in discussing survival times is very approximate.  One of the reasons is because of cancer statistics.

The statistic used in oncology is called median survival time.

A median is sort of like an average, but it is not an average per se.  When we talk about averages we are talking about some kind of a central tendency…a usable number, something we can latch on to in order to think about the best way to approach our dog’s cancer.

And we need to.  But, there is more to this story.  And you may like the ending.

When we use this number, all we are saying is that if cancer has a median survival time it means that in studies, the lifespan of half the patients was less than the median survival time, and the other half lived longer.

Hm.  When you think about it, there is less useful information here than we would like.

Here’s a secret that few know about concerning median survival time.  Median survival times can have what are called skews.  We can have left skews and right skews.

Let me clarify these skews.  Say we have a median survival time of 11 months for a given cancer.   What if we had 20 dogs in the study.  Half of the dogs would have lifespans less than 11 months, and the other half would live longer than 11 months. So ten live less than 11 months, and ten live more than 11 months.

Okay, here’s the interesting part.  If we have a left skewed distribution, the dogs who lived less than 11 months would have lifespans all over the board- maybe some at 2 months after diagnosis, a few at 3, more at 5, one at 7, a couple at 9.  That’s left-skewed: the dogs who lived less than the median survival time passed at a wide range of times.

Now, what about right skewed?  In a right skewed median survival time, the half dogs who lived more than 11 months in our example would have a wide range of survival times.  Maybe some at 12 months after diagnosis, a couple at 13, a few at 15, and one at 25, and one at 48 months.

25 months? 48 months?  Pretty far from 11 months. Of course, I am making these numbers up, but nonetheless, this stuff can happen.

So the good news here, and this is discussed in the upcoming second Guide edition I am writing with the help of oncologist Dr. Sue Ettinger, is that an cancer diagnosis is not an immediate death sentence.

True, we have to use statistics and data to inform our treatment plans.  But if a cancer has a median survival time that seems short, it does not mean that your dog will pass away at that exact time.  As a matter of fact, the odds are incredibly low that this will happen.

This is especially true if you are taking many more steps to help your dog than what were taken in the study used to create the median survival time for your dog’s cancer.

So, take median survival times with a grain of salt.  They are tools and nothing more. The only thing that can be said with any certainty is that if you predict your dog’s survival using median survival time, it will almost certainly be wrong.  Use them as the very rough, imprecise numbers they are.

By the way, Dr. Stephen Gould, one of the great thinkers of this century, was diagnosed with mesothelioma, likely caused by asbestos exposure.  The median survival time for this cancer  was 8 months.  He lived 20 years, ample time to write a great essay on median survival times.


Dr D

Leave a Comment

  1. Ed Capps on August 18, 2012 at 6:41 am

    Great commentary by all, but I grow sicker everyday of hearing cancer discussed in terms of extended survival, and quality of life. It is extremely frustrating that after all these years, and all the money that has been spent we aren’t taking outright cure! Thank God for people like Dr. D on the vet side, and Dr Bryzynski (sp) on the human side that have dared to think outside the mainstream box of cut,poison, and burn.

  2. DemianDressler on August 15, 2010 at 12:32 pm

    Thank you for your comments! I agree with everything you say. All my best,
    Dr D

  3. Buster & Buster on August 9, 2010 at 4:59 am

    Thanks for posting this! We always tell those who have cancer that there is no way of REALLY knowing exactly how long anyone with cancer ever has. I believe a lot has to do with will to live. In a previous posting you mentioned keeping life interesting and stimulating and I think that has a lot to do with it. We’ve had cancer patients who have lived years after a 2 day’s left diagnosis. I even have a grandfather who had lung cancer and was told he wouldn’t make it more than a month or so.. He lived 25 years to the age of 92! We have a dog who was told by a surgeon that if he didn’t have his diseased lung removed he wouldn’t survive a week and we’re now 10 years later and he is still chugging along. Having spent a lot of time in the ER one of the hardest things I think for people to hear is a time frame. They tend to think this is an absolute, but really hope it’s not. It’s so important to know everyone is an individual and time frames are just that.. an educated Guess. ( Thanks for referencing Stephen Jay Gould too! I had the pleasure of meeting him years ago when I worked at the Smithsonian in the archaeology dept! It’s nice to see him referenced!)

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