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Karyotype and FISH in leukaemia: why they change treatment | CION Cancer Clinics
Karyotype and FISH find broken, swapped or missing chromosomes in leukaemia cells. Some findings, such as the Philadelphia chromosome or the APL change, point straight to a specific medicine. Others place the leukaemia in a favourable, intermediate or adverse risk group, which shapes how intensive treatment is. These changes are almost always in the leukaemia cells only, not inherited. This page explains what your report means. At CION Cancer Clinics, our haematologist reviews abnormal blood reports with you, orders only the tests that answer your question and explains each result plainly.
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Medically reviewed by Dr. Basudev PokhrelConsultant Haematologist · last reviewed September 2026, next review due September 2027
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On this page
- Why do karyotype and FISH results change leukaemia treatment?
- How is a karyotype different from FISH?
- What happens to your sample for these tests?
- Which chromosome changes most often change the plan?
- What do families often misunderstand about chromosome results?
- What can karyotype and FISH not tell you?
- Common questions about karyotype and FISH
The short answer
Why do karyotype and FISH results change leukaemia treatment?
Karyotype and FISH look for broken, swapped or missing chromosomes in the leukaemia cells. Some of these changes point to a specific treatment, and others show whether the leukaemia is likely to be easier or harder to control. That is why two people with the same leukaemia name can be offered quite different plans.
What a chromosome is, in one line
Chromosomes are the packages that hold your genes. A normal cell has them in matched pairs. In leukaemia cells, pieces can break off and join the wrong chromosome, a whole chromosome can be lost or gained, or a piece can be turned the wrong way round. These changes happen in the leukaemia cells only. In most cases they are not inherited and cannot be passed to your children.
How the results feed into the plan
Your haematologist combines chromosome results with gene test results to place the leukaemia in a risk group, often called favourable, intermediate or adverse. The risk group helps decide how intensive treatment should be, and whether a stem cell transplant should be discussed early. A few findings point straight to a specific medicine.
The shorthand on your report, such as t(9;22) or inv(16), describes which chromosomes are involved and how. Your haematologist can translate each one for you.Two tests, two jobs
How is a karyotype different from FISH?
Karyotype
FISH
Looks at all the chromosomes at once
Looks only for specific changes chosen in advance
Needs living cells that divide in the laboratory
Works on cells that are not dividing
Can find unexpected changes
Can find small changes a karyotype misses
Usually takes longer
Often quicker, useful when a decision is urgent
Not sure whether this applies to you?
Ask an oncologistIn the laboratory
What happens to your sample for these tests?
A fresh sample
Usually part of the liquid marrow sample, sometimes blood. It needs a special tube and must reach the laboratory quickly, because the cells must be alive.
Growing the cells
For a karyotype, the cells are grown for a short time and stopped just as they divide, when chromosomes are easiest to see.
Staining and counting
The chromosomes are stained into a banded pattern. A specialist checks a set of dividing cells, pair by pair, for anything out of place.
Glowing probes for FISH
Fluorescent probes stick to chosen stretches of DNA. Under a special microscope, a missing, extra or joined signal shows the change.
Findings that matter
Which chromosome changes most often change the plan?
These are well-known examples, not a full list. What each means for you depends on the rest of your results.
t(15;17) in APL
The PML-RARA change defines acute promyelocytic leukaemia. It is treated with medicines such as all-trans retinoic acid and arsenic trioxide, rather than standard AML chemotherapy alone.
The Philadelphia chromosome
Written t(9;22) or BCR-ABL1. It defines chronic myeloid leukaemia and occurs in some ALL. Tablets that block this change, such as imatinib, are part of the plan.
t(8;21) and inv(16) in AML
Often grouped as core-binding factor leukaemia. These are generally placed in a favourable group, which can mean chemotherapy is used without an early transplant.
Changes linked to a harder course
Examples include a complex karyotype, loss of chromosome 7, and loss of part of chromosome 17. These often lead the team to discuss a transplant earlier.
Also tested in
- CLL, by FISH for 17p and 11q
- Myeloma, by FISH on plasma cells
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Do not wait for results if there is bleeding
Some leukaemias, especially APL, can cause dangerous bleeding before the chromosome results are back. If the person has bleeding gums that will not stop, nosebleeds, blood in vomit or urine, large new bruises, a sudden severe headache or confusion, go to the nearest emergency department now or call 108. Say that leukaemia is suspected. Treatment for APL is often started on suspicion, before FISH confirms it.
Commonly believed
What do families often misunderstand about chromosome results?
"A chromosome change means our children will get it too."
The changes found by these tests are almost always in the leukaemia cells only. They are acquired during life, not inherited. Rarely, a family pattern is suspected, and the team will say so and arrange separate testing.
"A normal karyotype means everything is fine."
A normal karyotype means no large chromosome change was seen. Many leukaemias with a normal karyotype carry important gene changes, which is why gene panels are often sent as well.
"An adverse group means nothing can be done."
It means the leukaemia may be harder to control, so the team plans more carefully and may discuss transplant early. Many people in this group still receive active treatment with a clear aim.
"We should not start anything until every result is back."
Some leukaemias need treatment within days. Your haematologist may start safely and adjust once results arrive. Ask what can wait and what cannot, rather than deciding on your own.
Being straight with you
What can karyotype and FISH not tell you?
These tests cannot, on their own, tell you how treatment will go or what the future holds. A risk group describes how a group of people with similar findings has tended to do. It does not decide what happens to one person. Age, fitness, other gene results and response to the first phase of treatment all matter.
When the test does not work
Sometimes the cells do not grow in the laboratory, and the karyotype report says "failed" or "no metaphases". This is not rare, especially with a poor or delayed sample. FISH and gene tests can often fill the gap, and a repeat sample is sometimes needed.
What to ask your haematologist
Ask which chromosome changes were found and what each means for the plan. Ask which FISH probes were used and whether gene tests were sent too. Ask which risk group the results point to, and whether transplant should be discussed. At CION, our haematology team reads these results with the rest of your tests, presents the case to a tumour board, and coordinates testing and care with qualified laboratories and transplant centres.
Laboratories report chromosome changes in a standard shorthand, but panels and wording differ. Keep every original report.Questions we are asked
Common questions about karyotype and FISH
How long do karyotype and FISH results take?
FISH is often quicker, because the cells do not need to grow first. A karyotype usually takes longer, because the cells must divide in the laboratory. Timings vary between laboratories. Ask your team when each result is expected, and whether any treatment can safely begin before then.
What does 46,XX or 46,XY mean on the report?
It is the standard way of writing a normal set of chromosomes for a woman or a man. If that is all the report says, no large chromosome change was seen in the cells examined. Gene tests may still find smaller changes that matter.
What does the "t" in t(9;22) mean?
The "t" stands for translocation, meaning pieces of two chromosomes have swapped places. The numbers inside the brackets name the chromosomes involved. Similarly, "inv" means a piece is turned round, and "del" means a piece is missing.
Is this the same as a genetic test for the family?
No. These tests look at the leukaemia cells, and the changes are almost always acquired, not inherited. Family members do not need testing because of these results. If a transplant is planned, brothers and sisters may be asked for a separate matching test, which is a different thing.
What if the karyotype failed?
It happens when the cells do not grow in the laboratory. FISH for the most important changes and gene panels can often answer the key questions instead. Your haematologist may ask for a repeat sample if something essential is still unknown.
Can the chromosome picture change over time?
Yes. If leukaemia comes back or progresses, new changes can appear. That is why the tests are sometimes repeated at relapse. After successful treatment, the original change may no longer be found, which is a useful sign the team tracks.
Are these tests done in Hyderabad?
Karyotype and FISH are offered by several specialised laboratories in the city. The sample must travel fresh and quickly. Ask your treating team which laboratory will test it, how the sample will reach there, and when the report is expected.
Are these tests covered by schemes or insurance?
They are often covered as part of an approved leukaemia workup. Rules differ between Aarogyasri, CGHS, ECHS, EHS, PM-JAY and private insurers, and they change over time, so check the current rules for your card. Our helpline can check your cover with you.
Your Haematologist
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Dr. Basudev Pokhrel reviews blood counts, transfusion needs and blood disorders, and works with the CION tumour board on blood cancers.
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Sources
- American Cancer Society — Acute Myeloid Leukemia (AML) Subtypes and Prognostic Factors
- National Cancer Institute — Definition of fluorescence in situ hybridization
- National Cancer Institute — Definition of Philadelphia chromosome
- Cancer Research UK — Acute myeloid leukaemia (AML)
- Leukemia & Lymphoma Society — Acute Myeloid Leukemia
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.
Keep reading
Related pages
Risk Stratification: Favourable, Intermediate, AdverseHow these results place you in a risk groupMyeloid NGS Panels: What Gets Tested and WhyThe gene tests sent alongsideWaiting for Molecular Results Before Starting TreatmentWhat can start before every result is backReading an Immunophenotyping PanelThe marker test that names the cell type
Talk to us
Waiting on chromosome results?
Send us the report or call the helpline. Our haematology team will explain what has been found and which results are still to come.