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My dog's mast cell tumor report says no mitosis. What does that mean?

Updated On September 23rd, 2025

Pet's info: Dog | Mixed Breed Large (61lb +) | Male | neutered | 10 years and 4 months old | 77 lbs

My dog has recently undergone mast cell tumor surgery and I am having some trouble understanding the lab report. Would you mind explaining it to me and the severity of the situation. Also, I do understand that the surgical margins were not clean, this was expected since the tumor was on his paw/leg area. I mostly want to understand what it means for mitosis not to be visible. Thank you!

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2 Answers

Most Helpful Answer

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Answered By Lauren Kennedy, DVM

Veterinarian

Published on May 27th, 2017

I'm so sorry poor Barney had to have surgery! It can be common with mast cell tumors removed from the limbs to not have clean margins because there isn't a lot of tissue to work with in that area. This doesn't necessarily mean the tumor will return but it does increase the chances. If the pathologist noted that no mitosis was seen this means they did not see any cells in the active stage of dividing. With very malignant tumors there will generally be a lot of mitosis or cell division seen. I hope Barney recovers from his surgery well and that this is the only one he needs!

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    Answered By Lauren Jones VMD

    Veterinarian

    Published on

    Mitosis indicates that cells are dividing and sometimes also refers to "mitotic figures" (I.e. dividing cells seen microscopically). Generally speaking, not seeing mitosis is a good finding because tumors that are more aggressive tend to divide more rapidly, causing more mitotic figures to be seen microscopically. I hope this helps to clarify things for you and that all goes well for Barney!

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