Many dog lovers really struggle with decisions in dog cancer care.

One reason is that there are so many uncertainties.  Ethical questions by nature do not have black and white answers.   Median survival times are basically just a type of average, and may not hold for a given dog.  Side effects are all just probabilities, and you never know if your dog’s number will come up in the roulette wheel.  Data on unconventional therapies is lacking.

So it can be incredibly frustrating when you and your canine companion are in this “gray zone”.

One of the reasons you are here is to try to lessen uncertainties by getting more information. So let’s look at some data that can help you guide the treatments for your dog, in particular in those borderline cases where we are not sure how the cancer will behave.

The most common instance of this is the grade 2 mast cell tumor.  As many know, the grade is a measure of how aggressive a cancer is.  When we say a cancer is a “high grade malignancy”, this means it is hard to cure.  A “low grade” growth is easier to cure as a generality (but not always), usually by surgical removal.

In mast cell tumors, the grade is broken down into three levels, with grade 1 being the lowest and grade 3 being the highest and most aggressive.  Aggressive cancers are those that do things like regrow after surgery, spread to surrounding areas (local invasion), or spread to distant sites to places like the spleen, liver, bone marrow, or other remote areas (metastasis).

Grade 2 mast cell tumors are intermediate, by definition, and unpredictable.  Or at least they have been in the past. In other words, grade 2 mast cell tumors can sometimes behave aggressively (like grade 3’s) or other times behave like more benign growths (grade 1’s).

If your dog’s pathology report (after the growth is biopsied) shows a grade 2 mast cell tumor, what is the action plan? A second wide excision surgery? Chemotherapy? We are in limbo…unless we consider another bit of information:

The mitotic index!

This is a measure of how many cells are dividing within the tumor.  The more cells that are dividing, the more aggressive a given tumor is generally.  Mitosis in this case is simply the process of cell division.  More cell division, faster growth, higher mitotic index.

The pathologist simply looks at a slide with a very thin slice of your dog’s tumor tissue on it, which has been stained so it is colored.  They can tell which cells are dividing (in mitosis). They simply count the numbers of these cells and viola, the mitotic index is calculated.

What is the data?

Lower mitotic index is better. This means that fewer dividing cells means a less aggressive cancer. The magical numbers for a grade 2 mast cell tumor is a mitotic index of 5 or less.  These dogs, with conventional care alone, have a median survival time of 70 months.

However, dogs with a mitotic index of greater than 5 had a dramatically shorter median life expectancy of only 5 months. This is quite a dramatic difference.

Here is the abstract.

So in those cases where we have a grade 2 mast cell tumor with a mitotic index of under 5, a wide excision should be done at a minimum, but the other steps (chemo, radiation) should be carefully considered before jumping in.  Do they make sense?

in cases where we are looking at grade 2 mast cell tumors with a mitotic index of greater than 5, these cancers should be considered very , very dangerous and aggressive.  For those who have a dog much less than her average life expectancy, be more aggressive with the treatments. Consider chemo and radiation with your oncologist.  For those whose dog is close or beyond his average life expectancy, it is time for ethical considerations and focus on life quality enhancement.

Diet, supplements, life quality enrichment, and the other complementary aspects of care should always be on your radar, regardless of grade or mitotic index.

For those who would like more on treatment plan analysis, check out The Dog Cancer Survival Guide.

Best,

Dr D

About the Author

Dr. Demian Dressler, DVM is known as the "dog cancer vet" and is author of Dog Cancer Survival Guide: Beyond Surgery, Chemotherapy & Radiation. Visit his blog and sign up free to get the latest information about canine cancer. Go to http://DogCancerBlog.com.

 

Dog Cancer