Pathology reports

What Is a High — Ki-67 Percentage?

A Ki-67 number on your report is not a survival score. It measures how fast tumour cells were dividing in your sample — and what counts as high depends entirely on which cancer type you have.

Medically reviewed by Dr. Muralidhar Muddusetty, Surgical Oncologist, MBBS (AIIMS) · MS Surgery (AIIMS) · DNB Surg Onc · MRCS (Edinburgh) · Last reviewed September 2026

Not a survival score — Ki-67 measures cell division speed, not how long you will live or how you will respond to treatment.
The cut-off depends on your cancer type — A number that is high in breast cancer sits in a different category than high in a neuroendocrine tumour.
One input, not the whole picture — Your oncologist reads Ki-67 alongside grade, stage, receptor status, and your overall fitness.
Borderline results are common — A result near the cut-off is interpreted cautiously, alongside other information, not acted on alone.

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Ki-67 measures what proportion of tumour cells are actively dividing. It is not a survival score. What counts as high depends on your cancer type: ASCO and WHO set different thresholds for different diseases. Your oncologist reads your number alongside stage, grade, and receptor status before making any treatment decision.

What counts as high Ki-67?

Cancer type	Guidance body	How Ki-67 is used	What 'high' means in this setting
Breast cancer	ASCO / CAP	Categorises tumour biology alongside hormone receptor and HER2 status	ASCO guidance places the threshold for high Ki-67 at 20% or above; below that range is low or intermediate
Neuroendocrine tumours (NET)	WHO	Used as the primary grading marker — G1, G2, or G3	WHO 2022 classification uses 3% and 20% as the boundaries between grades; above 20% is G3
Lymphoma	NCCN / ESMO	Noted in the report but not the primary decision marker	Interpretation depends on subtype; treatment decisions rely more on histological subtype and stage
Other solid tumours	NCCN / ESMO	Used alongside grade, stage, and other markers	No universal threshold; the same number carries different weight in different tumour types

What do the words on my Ki-67 report mean?

Ki-67: A protein found only in cells that are currently dividing. The percentage on your report shows what fraction of tumour cells were carrying this protein when the sample was examined.
Proliferation index: Another name for the Ki-67 percentage. Some laboratories use this term; it means the same thing.
Immunohistochemistry (IHC): The staining technique used to make Ki-67 visible under a microscope. A chemical dye marks positive cells so a pathologist can count them.
Cut-off: The threshold that separates low from high for a given cancer type. Set by bodies such as ASCO or WHO and differs between diseases.
High proliferative index: The tumour's Ki-67 falls in the upper range for its type, as defined by the relevant guideline. It does not mean the same thing across all cancers.
Mitotic index: A related but different count. This measures cells caught actively dividing at the exact moment the sample was taken. Some reports give both figures alongside Ki-67.

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Why does the same Ki-67 number mean different things in different cancers?

Ki-67 is counted in a tissue sample, and the result varies depending on which part of the tumour was examined, how the sample was prepared, and whether a pathologist or software performed the count.

Because of this variability, each cancer type has its own guideline — developed from clinical studies in that specific disease — rather than one universal threshold.

A number that is low in one cancer type may be high in another. Your report should always be interpreted by someone who knows which threshold applies to your diagnosis, your stage, and your other results.

What does Ki-67 actually tell my doctor?

Ki-67 tells your oncologist how fast the tumour cells were reproducing at the time the sample was taken. Faster reproduction is associated with more active tumour behaviour in many cancer types.

It does not tell your team whether the cancer has spread, how you will respond to treatment, or what your outlook is. It is one variable in a set of results read together.

Your oncologist combines Ki-67 with hormone receptor status, HER2 status, tumour grade, and stage before making a recommendation. No single marker decides the treatment.

If your Ki-67 surprised you, or you do not understand what it means for your specific situation, that is exactly the question to raise at your next appointment.

What else should I know about my Ki-67 result?

Is a higher Ki-67 always worse?

No, it is not that simple. In some cancers, tumours with a higher Ki-67 may respond well to chemotherapy precisely because rapidly dividing cells are more vulnerable to it. In others, a high Ki-67 is associated with more aggressive tumour behaviour. What the number means clinically depends on the cancer type and the treatments available for it — which is why your oncologist interprets it, not you from the report alone.

Can Ki-67 change between biopsy and surgery?

Yes, and this is well documented. The sample taken at biopsy may not represent the whole tumour, and Ki-67 can vary from one part of a tumour to another. It can also change after treatment — Ki-67 measured on a surgical specimen after chemotherapy is sometimes used to assess how much the tumour responded. If two results in your notes appear different, ask which sample each came from and what the difference means.

Why does my Ki-67 differ from someone with the same diagnosis?

Ki-67 is counted manually or with software on a tissue sample, and results vary depending on which part of the tumour was sampled, how the sample was prepared, and who or what performed the count. This is a known limitation of the test, not a sign that one result is wrong. It is one of the reasons guidelines bodies recommend combining Ki-67 with other markers rather than treating it as a standalone decision point.

Does Ki-67 tell you whether the cancer has spread?

No. Ki-67 measures how fast the tumour cells in the sample were dividing — it says nothing about whether cancer cells have moved to lymph nodes or other organs. That information comes from staging investigations: imaging, sentinel lymph node biopsy, or other tests. Stage and Ki-67 are separate pieces of information and are always reported separately.

What if my Ki-67 is exactly on the cut-off?

A result at or near the cut-off for your cancer type is often described as borderline, intermediate, or equivocal. Your oncologist will weigh it together with other factors — grade, stage, receptor status, and your overall fitness — rather than making a decision based on the number alone. Ask what your result means in the context of your complete report, not in isolation from it.

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Common questions

Frequently asked questions

My report says Ki-67 is 20%. Is that high?

Whether 20% is high depends on your cancer type, not the number alone. In breast cancer, ASCO guidance places 20% at the boundary of what is considered high. In a neuroendocrine tumour, the same number sits in a different grade category under WHO classification. Ask your oncologist directly: is this result high for my cancer type, and does it change my treatment plan?

What is the difference between Ki-67 and tumour grade?

Grade and Ki-67 measure overlapping but different things. Grade is an overall assessment of how abnormal the cells look under a microscope, including structural features. Ki-67 is one specific number — the proportion of cells actively dividing. In some cancer types a high Ki-67 contributes to a high grade. In others, the two are reported separately and can point in different directions.

Can Ki-67 change after I start treatment?

Yes. Ki-67 can fall significantly after chemotherapy or hormone therapy, and in some cancer types this change is measured to assess response. The Ki-67 on your original biopsy and a Ki-67 measured after treatment are different readings answering different questions. If your notes show more than one Ki-67 value, ask what each sample was and what the change means in your situation.

Do all laboratories measure Ki-67 the same way?

No, and this is a known limitation. Different laboratories use different antibodies, counting methods, and software, so the same tumour can produce slightly different readings at different centres. This is one reason guidelines bodies recommend treating borderline results cautiously and combining Ki-67 with other information. If you are seeking a second opinion, ask about the laboratory method used at each centre.

What questions should I ask my oncologist about Ki-67?

Ask: is this result high for my specific cancer type and stage? And: does this number change your recommendation? Those two questions are more useful than asking whether the number itself is good or bad, because the same result means different things in different tumours. Also ask whether the result was clearly in one range or borderline, since that affects how much weight your team places on it.

Is a low Ki-67 a good sign?

A low Ki-67 means fewer tumour cells were actively dividing when the sample was taken. In many cancer types that is associated with less rapid tumour growth — but it does not mean the cancer is harmless or that no treatment is needed. Treatment decisions depend on stage, cancer type, receptor status, and overall health alongside Ki-67. Ask your oncologist what a low result means specifically for your diagnosis.

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