Mitotic Figure: Definition

by Jason Wasserman MD PhD FRCPC
March 23, 2026

Mitosis is the process by which one cell divides to produce two identical cells. A mitotic figure is a cell caught in the act of dividing and visible under the microscope. Pathologists count mitotic figures because the number of dividing cells in a tissue sample is one indicator of how quickly a tumour is growing.

Why does cell division matter in a pathology report?

All cells in the body divide, but they normally do so slowly and in a controlled way. In cancer, cells can divide much more rapidly and without the usual controls. By counting the number of mitotic figures visible under the microscope, the pathologist gets a rough measure of how active the tumour cells are. A higher mitotic count often — though not always — suggests that the tumour is growing more quickly.

How is the mitotic count reported?

Pathologists count mitotic figures within a defined area of tissue on the glass slide. The result is usually reported as a number per high-power field (HPF) or per 10 HPFs—for example, “3 mitotic figures per 10 HPFs.” Some reports use a standardized area measured in square millimetres instead.

Different tumour types use different thresholds to define what counts as a high or low mitotic rate, so the significance of the number depends on the type of cancer being examined. Your doctor or specialist can explain what the count means for your specific diagnosis.

What does a high mitotic count mean?

A high mitotic count means that many cells in the sample were actively dividing at the time the tissue was removed. This can be a sign that a tumour is more aggressive, but it is only one piece of information. The mitotic count is almost always interpreted alongside other features, such as:

• Tumour grade – an overall score that reflects how abnormal the tumour cells look and how quickly they are likely to grow.
• Necrosis – areas of dead tissue within the tumour, which can also suggest aggressive behaviour.
• Tumour size and stage – how large the tumour is and whether it has spread beyond its original location.

No single finding tells the whole story. Your medical team will use all of these features together to guide decisions about your care.

What does a low mitotic count mean?

A low mitotic count suggests that fewer cells were actively dividing in the sample. This is generally a favourable finding and is often associated with slower-growing tumours. However, a low mitotic count does not always mean a tumour is harmless — other features of the tissue still need to be considered.

Does the mitotic count appear in all pathology reports?

No. Mitotic counts are most commonly reported for certain types of cancers and tumours, including:

• Soft tissue tumours (such as sarcomas)
• Breast cancer (as part of the Nottingham grading system)
• Gastrointestinal stromal tumours (GIST)
• Neuroendocrine tumours
• Melanoma

For many other cancer types, the mitotic count may not be specifically mentioned, even though cell division remains part of the overall grade.

Questions to ask your doctor

• What was the mitotic count in my report, and what does it mean for my diagnosis?
• Is the mitotic count used to determine the grade or stage of my tumour?
• How does the mitotic count influence my treatment plan?
• Are there other features in the report that are more or less important than the mitotic count?