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CION Cancer Clinics
Cascade testing: how a result moves through a family | CION Cancer Clinics
Cascade testing is how one person's inherited result is offered, step by step, to their blood relatives. Once a fault is confirmed, parents, brothers, sisters and adult children can be tested for that exact fault with a simpler test. Those who carry it are watched more closely. Those who do not can usually return to ordinary screening. This page explains the order, the steps and the limits. At CION Cancer Clinics, our team helps carriers and their families plan checks, next steps and support after a genetic result.
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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 cascade testing, in plain words?
- Who is offered testing, and in what order?
- How does a result move through a family?
- What do the words in a cascade mean?
- What happens after a relative tests positive or negative?
- Four things families assume about cascade testing
- What this page cannot tell you
- Common questions about cascade testing
The short answer
What is cascade testing, in plain words?
Cascade testing means offering a genetic test to blood relatives once one person in the family has been found to carry an inherited fault. The test looks only for that one known fault. It moves outward through the family one circle at a time, which is where the word cascade comes from.
It starts with one confirmed result
Nothing cascades until someone has a clear result. That person is usually the relative who already had cancer and was tested first. Their report names the gene and the exact spelling change. That detail is what makes testing everyone else simple, quick and far cheaper than the first test was.
Why families bother
A relative who carries the fault can start scans earlier and plan with their doctor. A relative who does not carry it can usually stop worrying and return to ordinary screening for their age. Both answers are useful. In practice, the relief of a clear result is what most families remember.
Cascade testing only works when there is a known fault to look for. Without one, relatives are watched from the family history instead.The circles of the family
Who is offered testing, and in what order?
Testing moves outward from the person with the result. Each circle is offered testing only after the circle before it has been checked.
The closest circle
Parents, brothers, sisters and adult children. Each of them has an even chance of sharing a fault that follows the usual dominant pattern. They are offered testing first.
Usually includes
- Mother and father, if living
- Full brothers and sisters
- Sons and daughters who are adults
The next circle out
Aunts, uncles, nieces, nephews, grandparents and grandchildren. Their chance of carrying the fault is lower. It becomes clearer once the relative who links them has been tested.
First cousins and beyond
Cousins are reached through their own parent. If your aunt tests positive, her children move into the closest circle for her. The cascade restarts from each new carrier.
Who is left out
Relatives by marriage share none of your genes and are never part of the cascade. A spouse is still worth involving, because your children carry half of their genes too.
Not sure whether this applies to you?
Ask an oncologistStep by step
How does a result move through a family?
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One person receives a confirmed result
A counsellor explains it, checks that the fault is classed as pathogenic, meaning known to raise risk, and gives the person a copy of the report to keep.
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The counsellor draws up a list of relatives
Together you mark who is at risk, who is still living, and who you are in touch with. The list usually covers both sides of the family.
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You pass the news on
Most relatives hear it from the person tested, not from the clinic. A family letter from the counsellor explains the fault and the test, so you do not have to explain the genetics yourself.
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Each relative sees a counsellor of their own
Testing a well relative is a personal decision. They get their own appointment, their own time to think and their own right to say no.
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A targeted test checks for the one fault
The laboratory looks only at the spelling change already found. This is simpler than the first test, and the answer is usually a clear yes or no.
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Each new carrier opens the next circle
A relative who tests positive becomes the starting point for their own children and siblings. A relative who tests negative closes the question for their branch.
On the paperwork
What do the words in a cascade mean?
- Index case
- The first person in the family to be tested and found to carry the fault. Everyone else is tested against their result.
- Proband
- Another word for the person who brought the family to attention. You may see either word on a letter.
- First-degree relative
- A parent, brother, sister or child. They share about half of your genes.
- Second-degree relative
- A grandparent, grandchild, aunt, uncle, niece, nephew or half sibling. They share about a quarter of your genes.
- Targeted test
- A test that looks only for the fault already found in the family, rather than reading the whole gene or a panel of genes.
- Uptake
- How many of the relatives who could be tested actually are. In most families it is lower than doctors hope.
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Side by side
What happens after a relative tests positive or negative?
Relative carries the fault
Relative does not carry it
A screening plan starts, often earlier than usual
Ordinary screening for age and background applies
Their own children are offered testing
Their children do not need testing for this fault
Risk-reducing options can be discussed calmly
No risk-reducing steps are needed for this fault
A counsellor stays involved over time
Other family history may still be worth a look
Commonly believed
Four things families assume about cascade testing
"My sibling tested negative, so I am clear too."
Each child inherits separately. One brother can carry the fault and another can be clear. Only your own test answers the question for you.
"Only the women in the family need testing."
Men carry and pass on faults exactly as women do, and many faults raise risks for men as well. Leaving brothers and fathers out is one of the most common gaps in a cascade.
"We should test the children first, since they have the longest to live."
For faults that raise risk only in adult life, testing usually waits until a child can decide for themselves. The adults closest to the index case come first.
"If a parent is clear, the grandchildren must be clear."
That is usually right for the parent's own line. It says nothing about aunts, uncles or cousins on other branches, who still need their own route to a test.
Being straight with you
What this page cannot tell you
It cannot tell you which of your relatives should be tested first, or how urgently. That depends on the gene, on who is still living and on which cancers the fault is linked to. A genetic counsellor works this out with you from the family tree and the report itself.
It cannot read your result for you
What your specific variant means is a question for the counsellor who ordered the test. Two faults in the same gene can carry quite different risks. A report with a variant of uncertain significance, meaning a change whose effect is not yet known, should not be used to test relatives at all.
Who this does not apply to
Most people do not need this. If nobody in your family has a confirmed pathogenic result, there is nothing to cascade. Your doctor will use the family history to decide on screening instead. Tumour mutation testing, done on cancer tissue to guide treatment, is a different test and is covered under targeted therapy.
Questions we are asked
Common questions about cascade testing
Is the test for relatives the same as the first test?
No. The first test searched one or many genes for any fault. A relative's test looks only for the exact fault already found, so the laboratory knows precisely where to look. It is usually quicker and cheaper, and the answer is normally a plain yes or no.
Do my relatives need a copy of my report?
Yes, or at least the family letter that names the gene and the exact change. Without that detail the laboratory cannot run a targeted test. Keep a copy of your report somewhere safe and share it only with relatives who choose to be tested.
Can relatives who live far away be tested?
Usually, yes. A relative in another city or district can see a counsellor near them, or have a sample collected locally and sent to a laboratory. The family letter travels with them. Counselling by phone or video is often possible for the first conversation.
What if a relative does not want to be tested?
That is their right. Some people prefer not to know, at least for now. Give them the family letter and let them decide in their own time. Pressure tends to delay testing rather than speed it up.
Should my young children be tested now?
For most adult-onset cancer genes, no. Testing usually waits until your child is an adult and can make the choice for themselves. A small number of syndromes need childhood testing because screening begins young. Your counsellor will tell you which applies to your family.
Does a negative result for a relative mean no cancer risk?
It means they did not inherit this particular fault. Their risk drops back to roughly that of people their age. It does not remove the everyday risks everyone carries, so ordinary screening still applies.
Who pays for a relative's test?
In India the relative usually pays for their own targeted test. Because it looks for one known fault, it costs much less than the first test. Ask the counsellor for the current price before the sample is taken, and check whether any scheme you hold covers it.
How do I start the cascade in my family?
Ask the counsellor who gave you your result for a family letter and a list of relatives to contact. Start with parents, brothers, sisters and adult children. Call the CION helpline if you are not sure where a relative should go, and someone will guide you.
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)
Medical Oncologist
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Sources
- National Cancer Institute — Genetic Testing for Inherited Cancer Susceptibility Syndromes
- NHS — Predictive genetic tests for cancer risk genes
- MedlinePlus Genetics — What is genetic testing?
- Cancer Research UK — Inherited cancer genes and increased cancer risk
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
Who should be tested first and why it mattersWhy the relative with cancer is the best starting pointTesting first-degree relativesThe closest circle, in more detailWhat to send a relative: the family letterThe letter that carries the result to relativesHow far out in the family should testing go?When to stop widening the circle
Talk to us
Has someone in your family been given a genetic result?
Tell us what the report says and who in the family might need testing. We will help you find the right counsellor and plan the next step. One helpline serves every CION centre.