The short answer
Mitotic rate is a count of how many cells are actively dividing in a tissue sample. A higher rate suggests faster-growing cells, and it is one of the features that helps set a tumor's grade. It is one part of the picture, read alongside other results.
Mitotic rate counts how many cells are dividing in a sample.
A higher rate suggests cells are growing and dividing more quickly.
It is one of the features that helps determine a tumor's grade.
It is one part of the picture, not a diagnosis or outlook on its own.
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The full explanation.
The short version
Some pathology reports include a mitotic rate, sometimes called a mitotic count. In plain terms, it is a count of how many cells were in the act of dividing in the sample. Dividing is how cells multiply. So the count is a clue to how fast a tumor may be growing.
How it is measured
When a cell divides, it passes through a stage called mitosis. A pathologist can spot these dividing cells under the microscope. They are called mitotic figures. The pathologist counts how many appear within a set area of the sample and reports that as a number. More dividing cells means a higher mitotic rate.
What a higher rate suggests
A higher mitotic rate suggests the cells are growing and dividing more actively. That can point to a faster-growing tumor. A lower rate suggests slower activity. This helps explain the biology of a tumor. On its own, though, it is only one measurement.
How it fits with grade
Mitotic rate is one of the ingredients in a tumor's grade. Grade is a broader description of how abnormal the cells look and how quickly they may grow. It combines mitotic rate with other features, such as how closely the cells resemble normal tissue. In breast cancer, for example, the grade adds up three scores: how well the cells form normal structures, how abnormal the nuclei look, and the mitotic count. So mitotic rate feeds into grade rather than standing in for it.
Which features count, and how they are scored, differs from one cancer type to another.
Keeping it in perspective
It is tempting to read a single number as a prediction. Outcome depends on many things working together: the type of cancer, its stage, its grade, and the treatment. No one measurement decides the future. A higher mitotic rate does not automatically mean a poor outcome.
What to ask
Ask what your mitotic rate is and what it suggests. Ask how it fits into the overall grade. Ask how it might affect your treatment options. Your care team's reading of the full report is what applies to you.
Sources
Words to know
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Common questions
What does a high mitotic rate mean?
It means many cells in the sample were actively dividing when it was examined, which suggests the cells may be growing more quickly. A higher rate often contributes to a higher grade. But it is one feature among several, and your care team interprets it in context.
How is mitotic rate measured?
A pathologist counts the number of dividing cells (mitotic figures) seen under the microscope, usually within a defined area of the sample. The count is reported as a number, and it feeds into how the tumor is graded.
Is mitotic rate the same as grade?
Not exactly. Mitotic rate is one of the features that go into determining grade. Grade is a broader description of how abnormal the cells look and how fast they may grow, and it considers mitotic rate along with other characteristics.
Does a high mitotic rate mean a worse outcome?
A higher rate can suggest a faster-growing tumor, but outcome depends on many factors together — type, stage, grade, and treatment. No single number predicts the future. Your care team weighs the whole picture.
Questions to ask your doctor
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Sources last checked: 2026-08-11 what this meansLast updated: 2026-08-11Next planned review: 2027-07-14
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How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes. We do not employ clinicians and do not intend to — our work is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Editorial review complete — This page completed Cancer Explained's editorial checks (sources, safety, plain language, duplication). It has not been reviewed by a physician or other healthcare professional.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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