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Single-gene testing: when one gene is the right question | CION Cancer Clinics
Single-gene testing reads one gene from start to finish, looking for any fault that raises cancer risk. It is chosen when a family's cancers point clearly to one known gene, such as a rare eye cancer in a young child. For most families today, a panel of several genes is used instead. This page explains when one gene is still the right question, and what a result can and cannot tell you. 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 single-gene testing, and when is it used?
- When is one gene the right question to ask?
- What happens when a single gene is tested?
- What do the words on a single-gene report mean?
- How does a single-gene test compare with a panel?
- What this page cannot tell you
- Four things families believe about single-gene tests
- Common questions about single-gene testing
The short answer
What is single-gene testing, and when is it used?
Single-gene testing reads one gene in full, looking for any fault that could raise the risk of cancer. It is used when a family's pattern points so clearly to one gene that looking anywhere else would add little. For most families today, a panel that reads several genes together is offered instead.
Reading one gene, from end to end
A gene is a long instruction written in four chemical letters. A single-gene test reads every letter of that one instruction and compares it with the standard spelling. It also checks whether whole sections of the gene are missing or doubled, because a fault of that kind can be missed by reading the letters alone.
Why it is used less often than it once was
Not long ago, testing one gene at a time was the normal approach, and a family might move slowly from one gene to the next. Modern machines read many genes in the same run, so a panel often costs about the same and answers more in one go. Single-gene testing has not disappeared. It has narrowed to the situations where it genuinely fits.
Single-gene testing is different from checking for one known fault already found in a relative. That is a separate, simpler test.When it still fits
When is one gene the right question to ask?
A counsellor chooses a single gene when the pattern is specific enough to name the gene before testing. These are the usual situations.
A pattern that points to one gene
Some inherited conditions have one known cause and a very recognisable look. A child with an eye cancer called retinoblastoma, or a young adult with a very large number of bowel polyps, usually leads straight to one gene.
Examples you may hear
- RB1, for retinoblastoma in childhood
- APC, for many bowel polyps at a young age
- VHL, for tumours of the kidney, eye and brain in one family
- RET, for an uncommon thyroid cancer called medullary thyroid cancer
A syndrome doctors have already recognised
When the condition is clear from the examination and the scans, testing that one gene confirms it. The result then guides screening for the rest of the family.
A closer look after a panel
Sometimes a panel has already been done, the family story fits one gene very strongly, and nothing was found. A deeper look at that one gene, using a different method, can pick up faults the first test could not see.
When it does not fit
A mixed family history, with breast, ovarian, bowel and other cancers across relatives, rarely points to one gene. A single-gene test in that family can come back negative while the real fault sits in a gene nobody looked at.
Not sure whether this applies to you?
Ask an oncologistFrom referral to result
What happens when a single gene is tested?
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The family tree comes first
A genetic counsellor draws out who was diagnosed, with which cancer and at roughly what age, on both sides. That picture is what tells them one gene is the right place to look.
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Consent and a sample
You are told what the test can and cannot show, and what a result might mean for your relatives. A blood sample is taken, or occasionally saliva.
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The laboratory reads the gene
Every letter of the gene is read and compared with the standard spelling. A second method checks for missing or doubled sections of the gene.
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The report goes to the person who ordered it
Your counsellor or doctor reads it first, checks it against your family history, and books a results appointment rather than sending it by message.
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Relatives are offered a simpler test
If a fault is found, close relatives can be tested for that exact fault. That follow-on test is quicker and usually cheaper than the first one.
On your report
What do the words on a single-gene report mean?
- Sequencing
- Reading the letters of the gene one by one to look for spelling changes.
- Deletion and duplication analysis
- A separate check for whole sections of the gene that are missing or copied twice. Your report should say whether this was done.
- Pathogenic variant
- A spelling change known to break the gene. This is what a positive result means.
- Variant of uncertain significance
- A change the laboratory cannot yet classify. It is not a positive result and should not change your care.
- Negative result
- No fault was found in that one gene. It says nothing about genes that were not tested.
- Cascade testing
- Offering relatives a test for the exact fault already found in the family, one branch at a time.
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Side by side
How does a single-gene test compare with a panel?
Single-gene test
Multigene panel
Reads one gene in full
Reads several genes in the same run
Suits a pattern that points to one gene
Suits a mixed or unclear family history
Fewer uncertain results to explain
More uncertain results, spread across more genes
A negative leaves every other gene unchecked
A negative rules out more genes at once
Not always the cheaper option today
Often similar in price, depending on the laboratory
Being straight with you
What this page cannot tell you
It cannot tell you which gene, if any, your family should be tested for. That comes from a genetic counsellor who has drawn out your family tree and, where possible, arranged testing for the relative who already has cancer. Reading about genes online cannot replace that conversation.
It cannot read your report for you
What your specific variant means is a question for the counsellor who ordered the test. The same gene can carry harmless changes and serious ones, and only a trained reader can tell you which one you have. Please do not search the variant name and act on what you find.
Who this does not apply to
Most people do not need a single-gene test. If your family has one relative diagnosed with a common cancer at an older age, no gene may need testing at all. If your question is about faults inside a tumour rather than in the family, that is tumour testing, covered under targeted therapy.
If you are unsure whether your family history points to one gene, call the helpline and describe it. Someone will tell you honestly whether a referral makes sense.Commonly believed
Four things families believe about single-gene tests
"A negative single-gene test means our family has no inherited risk."
It means no fault was found in that one gene. Another gene could still be involved, and a striking family history is still taken seriously and watched on its own merits.
"Testing one gene is always cheaper than a panel."
It used to be. Many laboratories now read a panel on the same machine for a similar price, so the cheaper-looking option is not always the better value. Ask for both prices before you decide.
"My sister tested negative, so I must be negative too."
Each person inherits their own copy of each gene. A sister's negative result tells you about her, not about you. If a fault is known in the family, you need your own test for it.
"If they are testing only one gene, they are cutting corners."
A narrow test is often the more careful choice. When the pattern clearly fits one gene, reading that gene thoroughly gives a cleaner answer than reading many genes with only a loose link to your family.
Questions we are asked
Common questions about single-gene testing
Is single-gene testing the same as testing for a known family fault?
No. Single-gene testing reads the whole gene to find any fault. Testing for a known family fault looks only at the one spot where a relative's fault has already been found. The second test is simpler, and it is what most relatives are offered once the family fault is known.
Which conditions usually lead to a single-gene test?
Mostly rare, distinctive ones: retinoblastoma in a child, a very large number of bowel polyps, medullary thyroid cancer, or tumours of the kidney, eye and brain within one family. For common patterns such as breast, ovarian or bowel cancer, a panel is now more usual.
Is a blood sample enough?
Yes. For inherited testing a blood sample is normally enough, and saliva is sometimes used. Tissue from a tumour answers a different question about the cancer itself. If the relative with cancer has died, stored tissue from an old operation can sometimes be tested instead.
How long does the result take?
It depends on the laboratory, and on whether a second method is needed to check for missing or doubled sections of the gene. Ask the centre for its usual turnaround before the sample is sent. Results should be given in an appointment, not by text message.
My test was negative but my family history is strong. What now?
Go back to your counsellor. A negative result in one gene does not end the question. They may suggest a wider panel, a check for missing sections of the gene, or testing a different relative. Meanwhile, screening is planned on the family history itself.
Does a single-gene test cost less than a panel in India?
Not always. Prices vary widely between laboratories, and panels are now often priced close to single genes. Ask for the cost of both options and what each includes. Check with the centre before assuming insurance, Aarogyasri or Ayushman Bharat will pay for genetic testing.
Should my children have a single-gene test?
For faults that raise risk only in adult life, testing usually waits until the child is an adult and can decide. A few conditions tested one gene at a time, such as retinoblastoma and some bowel polyp conditions, do need childhood testing because screening starts young. Your counsellor will tell you which applies.
Can the counselling be done in Telugu?
Ask when you book. Asking questions in the language you think in makes a real difference to understanding a result. Bring a family member if it helps, and a written list of who was diagnosed with what, and at roughly what age, on both sides.
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
- National Cancer Institute — Genetic Testing for Inherited Cancer Susceptibility Syndromes
- MedlinePlus Genetics — What are the different types of genetic tests?
- NHS — Predictive genetic tests for cancer risk genes
- NCBI Bookshelf — GeneReviews
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
Targeted Mutation Analysis: Testing for One Known VariantThe simpler test relatives take once a family fault is foundMultigene Panel Testing ExplainedWhat most families are offered instead of one geneDeletion and Duplication AnalysisThe check for missing sections that letter-reading can missTypes of Genetic Test for Cancer: A Complete ComparisonEvery test type on one page, side by side
Talk to us
Not sure whether one gene or a panel fits your family?
Tell us who in your family was diagnosed and at what age. We will explain which test, if any, makes sense and arrange the referral. One helpline serves every CION centre.