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Dog cancer prognosis: What does a high mitotic index score mean?

Updated On September 23rd, 2025

Pet's info: Dog | Border Collie | Male | neutered | 6 years and 4 months old | 58 lbs

Hi there, how does a mitotic index score of 31/10 HPF convert into the standard <5 or >5? Since the standard of >5 or <5 is used to determine aggressiveness of the cancer? Please advise. My dog Chummy had a biopsy and results determined possible Spindle Cell Sarcoma.

2 Answers

Most Helpful Answer

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Answered By Andrea M. Brodie, DVM

Veterinarian

Published on December 31st, 2018

Mitotic index is defined as the ratio between the number of cells in a population undergoing mitosis to the total number of cells in a population. So your dog's mass' mitotic index being 31/10 (31 mitoses in 10 high power fields) would be (less accurately) fall into the category of >5 mitoses per 10 high power fields. This would mean that a mitotic index of 31/10 HPF designates a high grade malignant tumor.

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    Answered By Dr. Strydom, DVM

    Veterinarian

    Published on December 31st, 2018

    The mitotic index in a population of cells is the ratio of the number of cells undergoing mitosis (cell division) to the number of cells not undergoing mitosis. HPF means per high power field of the microscope. So with 31/10 means that 31 cells are dividing and 10 are not per every high power field.

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