Medical Oncologist
CION Cancer Clinics
Whole genome sequencing: what it reads and when it helps | CION Cancer Clinics
Whole genome sequencing reads almost all of your DNA, not only the genes linked to cancer. For most families it is not the right first test, because a targeted cancer panel answers the inherited question more cleanly. It earns its place when a strong family history has already tested negative, or when a rare syndrome is suspected. This page explains what it reads, what it adds and the uncertainty it brings. At CION Cancer Clinics in Hyderabad, our oncologists review your family history with you and guide you to the right genetic counselling and testing.
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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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On this page
- What is whole genome sequencing, in plain words?
- What can a genome find that a panel cannot?
- What actually happens when a genome is sequenced?
- The words on a genome report, in plain language
- How does a genome compare with a cancer gene panel?
- Four things families assume about genome tests
- What this page cannot tell you
- Common questions about whole genome sequencing
The short answer
What is whole genome sequencing, in plain words?
Whole genome sequencing reads almost every letter of the DNA you were born with. A cancer gene panel reads a chosen list of genes. An exome reads the working parts of all your genes. A genome reads all of that, plus the long stretches that sit inside and between genes.
Why the in-between stretches matter at all
Some faults that switch off a cancer gene do not sit in the working parts a panel reads. They hide deep inside a gene, or they are large pieces of DNA that are missing, doubled or moved. A genome reads across these more evenly, so it can find some faults that other tests walk past. Reading a stretch is not the same as understanding it, though. Much of the in-between DNA is still poorly understood.
A blood test, not a tumour test
On this page we mean a genome read from blood or saliva, looking for a fault you were born with and could pass on. Sequencing a tumour to choose a medicine is a different test with a different purpose. That belongs to targeted therapy, and your oncologist orders it.
More DNA read does not mean more answers. It often means more questions.What it adds
What can a genome find that a panel cannot?
The gains are real but narrow. They matter most for a family whose history is strong and whose earlier test found nothing.
Faults deep inside a gene
Some changes sit in stretches that are cut out before the instruction is used, yet they still spoil how the gene is read. A panel that reads only the working parts can miss them.
On a report this may say
- Deep intronic variant
- Splicing variant, often confirmed with an RNA test
Large missing or moved pieces
Deletions, duplications and pieces of DNA that have swapped places. A panel usually needs an extra method to look for these. A genome sees many of them directly in the same run.
Genes nobody thought to order
Every gene is read, so the stored data can be looked at again later for genes that were not on the first list. That can happen without a new sample, if the lab keeps the data and agrees to do it.
What it still cannot do
It cannot explain a change that nobody has seen before. It reads some repetitive stretches poorly. It also reads each letter fewer times than a panel does, so for the well-known cancer genes a good panel can be just as reliable.
A genome is wider, not deeper.Not sure whether this applies to you?
Ask an oncologistFrom sample to report
What actually happens when a genome is sequenced?
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Counselling comes first
A genetic counsellor draws your family tree and explains what a genome can and cannot find. You also decide whether you want to hear about serious findings unrelated to cancer.
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The sample is taken
A tube of blood or a saliva sample is enough. DNA is drawn out of the cells in the laboratory. No tumour tissue is needed for this test.
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The DNA is read in small pieces
The machine reads short fragments, each many times over. A computer then lines them up against a reference genome, like fitting torn pages back into a book.
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Millions of differences are filtered
Everyone differs from the reference at millions of letters, and almost all of these are harmless. The lab narrows them down to the genes that fit the question your counsellor asked.
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Scientists classify what is left
Each remaining change is weighed against published evidence and databases. It is reported as harmful, uncertain or harmless. This step takes longer than for a panel.
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The result is explained in person
Your counsellor goes through the report with you and your family. Ask how long the lab keeps the data, and whether it will look again as knowledge grows.
On your report
The words on a genome report, in plain language
- Genome
- All of your DNA, the complete set of instructions in every cell of your body.
- Exome
- The small share of the genome that carries instructions for making proteins. Most known cancer faults sit here.
- Coverage or depth
- How many times each letter was read. More reads give more confidence that a change is real and not a machine error.
- Structural variant
- A large piece of DNA that is missing, doubled, flipped or moved to another place.
- Germline
- Present from birth in every cell, and so able to pass to children. The opposite is somatic, meaning found only in the tumour.
- Secondary finding
- A result about a serious, treatable condition that was not the reason for the test. It is reported only if you agreed beforehand.
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Side by side
How does a genome compare with a cancer gene panel?
Whole genome
Targeted cancer panel
Reads almost all of your DNA
Reads a chosen list of cancer genes
Sees many large rearrangements directly
Needs an extra method for large changes
More uncertain results to explain
Fewer uncertain results
Costs considerably more and takes longer
Cheaper and quicker to report
Stored data can be looked at again later
New genes usually mean a new test
Commonly believed
Four things families assume about genome tests
"A genome test finds everything."
It reads almost everything and understands far less. Some stretches are read poorly, and many changes found cannot yet be explained. It describes risk. It does not predict a future.
"If the panel was negative, a genome will find the real answer."
Sometimes it does. More often it finds nothing new. Many families with a lot of cancer have no single faulty gene behind it, and a bigger test cannot find a fault that is not there.
"The biggest test is always the safest choice."
A bigger test brings more uncertain results, more unexpected findings, more cost and a longer wait. The right test is the one that answers your family's question cleanly.
"Once my genome is read, my relatives are covered too."
Your data belongs to your test. If a fault is found, each relative still needs their own sample, tested for that exact fault. That targeted test is quicker and cheaper than a genome.
Being straight with you
What this page cannot tell you
It cannot tell you whether a genome is the right test for your family. That depends on who was diagnosed, with what, at what age, and what has already been tested. A genetic counsellor weighs all of that before suggesting any test.
It cannot read a result you are holding
A genome report can list changes in genes you have never heard of. What your specific variant means is a question for the counsellor who ordered the test. Please do not search for it online and act on what you find.
Why Indian results can be harder to read
The big reference databases were built mostly from people of European ancestry. A change that is common and harmless in Telangana may look rare and suspicious on a report. Indian reference data is growing, including from the national GenomeIndia project, but gaps remain. Communities where marriage within the family or caste is common can also carry their own rare variants.
Who this does not suit
Most people do not need a genome. If nobody in your family has been tested yet, a targeted cancer panel on the relative who had cancer is the usual first step.
Unsure which test fits your family? Call the helpline and describe your history. Someone will tell you honestly.Questions we are asked
Common questions about whole genome sequencing
Is whole genome sequencing the same as exome sequencing?
No. An exome reads only the parts of genes that carry protein instructions, which is a small share of your DNA. A genome reads nearly all of it, including the stretches between genes. The genome is wider, costs more and produces more results that nobody can yet explain.
Should I ask for a genome instead of a panel?
Usually not as a first test. A cancer panel answers the inherited cancer question well for most families. A genome is worth discussing when a strong family history has already tested negative, or when a counsellor suspects an unusual syndrome. Your counsellor will say which applies.
How long does a genome result take?
Longer than a panel, because there is far more data to filter and check. The wait varies between laboratories and depends on how many changes need review. Ask the lab for its current turnaround before you give the sample, so you know what to expect.
What does it cost in India, and is it covered?
It costs considerably more than a standard cancer panel, and prices vary widely between labs. Private insurance and government schemes such as Aarogyasri and Ayushman Bharat rarely pay for inherited genome testing. Ask for the full price, including counselling, in writing before you agree.
Will it tell me about illnesses other than cancer?
Only if you agree. Because a genome reads every gene, it can pick up serious conditions of the heart or other organs. You decide before the test whether you want those reported, and you can say no. Talk it through with your family first.
Can my relatives use my genome result?
They can use what it found, not the test itself. If a harmful fault is found, brothers, sisters and children can each have a simple test for that exact fault. That test is quicker and cheaper than a genome, and the counsellor can write a family letter to explain it.
What happens to my genome data afterwards?
The lab stores it. Ask where it is kept, who can see it, how long it is held and whether it may be used for research. India's data protection law, the DPDP Act, gives you rights over your personal data. Get the lab's answers in writing.
Can my tumour be sequenced to choose treatment?
Yes, but that is a different test. Tumour sequencing looks for changes inside the cancer that a medicine can target. It is ordered by your oncologist and explained on our targeted therapy pages. It does not tell you on its own what you inherited.
Your Specialists
Meet CION's oncologists. Bring your family history or genetic report to them.
Our medical oncologists see people with a strong family history of cancer, arrange genetic counselling and testing where it fits, and plan the checks that follow.
Medical Oncologist
Dr. C. Raghavendra Reddy
MBBS(Gold Medal), DNB(General Medicine), DM(Medical Oncology)(Gold Medal)
Medical Oncologist
Dr. Bharati Devi Gorantla
MBBS, MD(General Medicine), DM(Medical Oncology)(Adyar,Chennai), ECMO, MRCP SCE(UK)
Medical Oncologist
Dr. Owais Mohammed
MBBS, MD (General Medicine), DrNB (Medical Oncology), ECMO, MRCP SCE (Medical Oncology) (UK)
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Sources
- MedlinePlus Genetics — What are whole exome sequencing and whole genome sequencing?
- National Cancer Institute — Genetic Testing for Inherited Cancer Susceptibility Syndromes
- MedlinePlus Genetics — What are secondary findings from genetic testing?
- Cancer Research UK — Genetic testing for cancer risk genes
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
Whole exome sequencing explainedThe narrower sibling test, and when it is enoughExome vs genome vs panelAll three tests compared on one pageWhy a bigger panel is not always betterThe hidden cost of testing more genesSecondary and incidental findingsWhat to decide before a wide test finds something unexpected
Talk to us
Is a genome the right test for your family?
Tell us who was diagnosed, with what, and what has already been tested. We will tell you honestly whether a genome adds anything over a panel. One helpline serves every CION centre.