Medical Oncologist
Deciding on chemotherapy
Genomic test vs Ki-67 and grade: why they can disagree
They disagree because they measure different things. Grade describes how abnormal the cells look. Ki-67 measures how many are dividing. A genomic score predicts what chemotherapy would add. Three questions, three answers. This page explains which one carries most weight for the chemotherapy decision, and what to do when yours conflict.
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Medically reviewed by Dr. Naresh GunduConsultant Medical Oncologist · MBBS, DNB (Internal Medicine), DM (Medical Oncology, AIIMS) · last reviewed September 2026, next review due September 2027
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The short answer
Why do my Ki-67, my grade and my genomic score disagree?
Because they measure different things. Grade describes how abnormal the cells look. Ki-67 measures how many are dividing. A genomic score reads the activity of a set of genes and predicts what chemotherapy would add. Three different questions can honestly give three different impressions.
Which one your team trusts most
For the chemotherapy decision, the genomic score is generally given the most weight, because it was built and validated specifically to answer that question. Grade and Ki-67 were not.
Why the others still matter
They are cheap, immediate and available on every report. Where no genomic test is being done, grade and Ki-67 are among the main things your oncologist reads. They are useful. They are just less precise for this particular decision.
A disagreement between them is common, expected, and not a sign that any laboratory made an error.On your report
What each measure actually is
- Grade
- A score from one to three describing how abnormal the cells look under the microscope. Judged by eye, so it carries some variation between pathologists.
- Ki-67
- A stain showing how many cells are actively dividing, reported as a proportion. It is useful but notoriously variable between laboratories.
- Mitotic count
- A direct count of dividing cells, and one of the components that makes up the grade.
- Genomic recurrence score
- A number from a validated panel of genes, predicting what chemotherapy would add on top of hormone tablets.
- Luminal A and luminal B
- Biological groupings of hormone sensitive cancers. Ki-67 is often used to separate them, which is one reason it appears on reports.
- Validated
- Tested in a designed study and shown to predict what it claims to. This is where the genomic score has the clearest advantage.
Why they diverge
Four reasons these results can point different ways
None of these means a mistake was made. They are properties of the tests themselves.
They ask different questions
How abnormal the cells look, how fast they divide, and how much chemotherapy would help are three separate matters. A cancer can look alarming and still gain little from chemotherapy.
Ki-67 is hard to standardise
The result depends on which part of the tumour was counted and how. The same tissue sent to two laboratories can come back with noticeably different figures, which is a known weakness.
Treat a borderline Ki-67 with caution.Grade is a judgement made by eye
Experienced pathologists agree most of the time and differ at the boundaries. A cancer sitting between two grades may be reported differently by two competent people.
The genomic score reads other things too
It includes genes related to hormone receptors and to HER2, not only to growth. That is precisely why it can give a different answer from a pure measure of how fast cells divide.
Ask your oncologist
- Which measure are you relying on
- Why that one, for my case
- What would change your mind
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Side by side
Strengths and weaknesses of each
What it is good for
Where it falls short
Grade: free, on every report, a useful overall guide
Judged by eye, and varies at the boundaries
Ki-67: quick measure of how fast the cancer divides
Varies between laboratories and is hard to compare
Genomic score: built and validated for the chemotherapy question
Expensive, slow, and only for one subtype
All three: available to your oncologist together
None of them predicts what will happen to you personally
Being straight with you
What to do when the results conflict
A conflict is information rather than a problem. It usually means your cancer sits in a genuinely borderline place, which is exactly the situation where taking the decision carefully pays off.
Ask which measure is driving the recommendation
A straightforward question with a straightforward answer. If your oncologist is relying on the genomic score, ask why they are setting the grade aside. If they are relying on the grade, ask what would make them order a genomic test.
Do not go shopping for the answer you want
Running another test hoping for a more comfortable result is a common impulse and a poor plan. You end up with three numbers, no way to choose between them, and a decision that is harder rather than easier.
What none of them can tell you
None of these measures predicts your future. They estimate what is likely across groups of people who resemble you. Your oncologist is using them to choose between two treatment plans, which is what they are good for, and not to forecast your life, which is something no test in breast cancer can do.
Write down which one decided it
At the end of the appointment, ask your oncologist to say in one sentence which measure drove the recommendation, and write that sentence down. Months later, when a relative sends you an article about Ki-67 or a neighbour describes a different plan, that one line will save you from reopening a decision that was made carefully the first time.
Commonly believed
What people conclude from conflicting numbers
One of the laboratories must have made a mistake.
Almost never. The tests measure different things, so different answers are expected. A genuine error would usually show up as a result inconsistent with the whole report, and that is worth raising specifically if you see it.
A high Ki-67 means I definitely need chemotherapy.
It is one input and among the least standardised. Where a genomic score is available and points the other way, most oncologists will give the genomic score more weight, because it was validated for exactly this decision.
A grade 3 cancer is always aggressive.
Grade 3 describes appearance under the microscope. Some grade 3 hormone sensitive cancers score low and gain little from chemotherapy. Appearance and behaviour are related but they are not the same thing.
I should get every test available to be thorough.
More numbers do not produce more clarity when they measure different things. The useful question is which single measure your oncologist will act on, and why. Ask that rather than collecting results.
Questions we are asked
Common questions about conflicting results
My Ki-67 is high but my genomic score is low. Which wins?
For the chemotherapy decision most oncologists give the genomic score more weight, because it was built and validated for that question. Ask your own oncologist to say explicitly which they are relying on and why.
Can Ki-67 be repeated?
It can, but repeating it often produces a different figure, because the test is hard to standardise. That variability is the reason it is treated as a supporting result rather than a deciding one.
Is grade more reliable than Ki-67?
Grade is better standardised and more consistently reported, though it is still a judgement made by eye. Both are useful as part of the picture. Neither was designed to answer the chemotherapy question on its own.
Should I have a genomic test because my grade and Ki-67 disagree?
It is a reasonable reason to raise it, provided your cancer is hormone positive and HER2 negative and the chemotherapy decision is genuinely open. Disagreement between the cheap measures is often exactly what the genomic test is there to settle.
My report has no Ki-67. Should it?
Not every laboratory reports it, and its absence is not a gap in your care. Your oncologist has the grade, the receptors, the HER2 result and the node status, which together carry more weight than Ki-67 does.
Does a low Ki-67 mean I can skip chemotherapy?
Not on its own. It points that way in a hormone sensitive cancer but is not reliable enough to decide by itself. It is read alongside grade, size and nodes, and sometimes prompts a genomic test to settle the question properly.
Can my grade be reviewed?
Yes. A second pathologist can look at the same slides, and this is reasonable where the grade sits at a boundary and a real decision turns on it. Ask the hospital in writing for the blocks and slides.
Which number should I be watching afterwards?
None of them. Once treatment is decided, these numbers have done their job. What matters afterwards is completing the treatment, attending follow-up and reporting new symptoms rather than revisiting old results.
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Sources
- National Cancer Institute — Breast cancer gene expression tests
- Cancer Research UK — Grades of breast cancer
- Breast Cancer Now — Understanding your pathology results
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.