Monday, February 22, 2016

Dog mast cell tumor test results: 4 things to ask about

Sinead the Boston terrier recovering from a mast cell tumor
Last week, Sinead went in for her mast cell tumor removal surgery. I've decided to call it a "brow lift," as she lost some tissue over her left eye. Her expression is a little more open on that side than it is on the right. See the difference?

Anyway, since that surgery (and if you missed the original post with the gnarly tumor in all its glory, click here), I've been waiting for pathology reports. And I've been so worried about the pathology test, that I started hitting up Dr. Google, just so I'd be prepared.

I came up with 4 key things to ask about. And as a disclaimer: I'm no veterinarian. My words cannot be considered more useful than those a doctor would use. If you're looking for clinical advice, I'm the wrong gal. But, if you're interested in what one reasonable (and worried) person might look for in a pathology report, this blog might help. 

So here's what I asked about, along with Sinead's results.

And (spoiler alert): Sinead's test was pretty much perfect.

Question 1: What were the margins?

Mast cell tumors can have long legs. They can reach down and out into healthy tissue, and that invasion isn't always easy for a surgeon to see. A pathologist measures from the end of the tumor to the edge of the cut that took the tumor out. The bigger the margin, the better.

Sinead's margins were about a millimeter. That's not huge, but it means the whole tumor came out in this surgery.

Question 2: What was the grade?

Mast cell tumors are rated on something called the Patnaik system, which moves from 1 to 3. The higher the grade, the more dangerous the tumor is considered. This was the gold standard of mast cell tumors for years, but its fallen out of fashion with some doctors (more on that in a minute). But in general, no one wants to see a grade 3.

Sinead's was a grade 2. That's not wonderful, but it's not bad either.

Question 3: What is the secondary grade?

Many histopath professionals worry about these tumors, and they tend to give most of them grade 2 readings. It's a safe bet. So some professionals have suggested an up/down rule. Either the tumor is of a high grade (bad) or a low grade (good). Up or down. Obviously, you want a reading of low. 

Sinead's was a low grade.
Sinead the Boston terrier in the sun

Question 4: What was the mitotic index?

This is a technical term that describes, in essence, how many cells are dividing. Since cancer involves cells growing and dividing at a very fast clip, a high mitotic index points to areas of the body that are changing really fast. And that could point to cancer.

This is sort of the cutting edge of mast cell research (Wanna get geeky? Check out this study.). It's been closely tied to how long a dog lives with a mast cell tumor, regardless of grade. The lower the index, the better.

Sinead's mitotic index was less than 1. You really can't get a better result than that.

So overall, this is a really wonderful report. It's filled with a lot that I can be hopeful about. But, as the pathologist says, mast cell tumors can be sneaky. They can evade detection, and they can change in ways that no one can predict. So are we out of the woods? Not quite.

In a few weeks, I'll take Sinead to a veterinary oncologist for a second opinion. I'll write up more then.

But for now? It's time to celebrate!


  1. That's really wonderful and encouraging news! Celebrating along with you, and purring and praying that all continues to go well. Hugs to you and Sinead!

  2. She looks great ! Congratulations ! I know more about cat's health, but I always love when a disease can be healed for all animals.

  3. When facing something like this, you must celebrate the good news. We are celebrating with you.