Medical Oncologist
CION Cancer Clinics
Choosing who in the family tests first | CION Cancer Clinics
Wherever possible, the relative who already has cancer is tested first. Their result names the exact fault everyone else can then be tested for, or rules one out with more confidence than testing a well relative ever can. Here is how that choice is actually made, and what happens when the ideal candidate is not available. 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
- Who in the family should be tested first?
- How the right starting person is chosen
- How a counsellor actually reaches this decision
- Words a counsellor will use when planning the order
- Testing the affected relative first, or a well relative first
- What this page cannot tell you
- Four things families assume about who goes first
- Common questions about choosing who tests first
The short answer
Who in the family should be tested first?
Wherever possible, the relative who already has cancer. Testing that person first tells you whether there is a specific fault to look for at all, before anyone else who is well is asked to give a sample.
Why the affected relative goes first
A person who already has cancer is the most likely member of the family to carry a fault, if one exists. Their result is also the most informative one possible: a confirmed fault names the exact target for everyone else's test, and a clear negative result usually means the cancer in the family is not linked to a single inherited gene at all.
When that person cannot be tested
Sometimes the affected relative has died, declines, or cannot be reached. Testing can still start with the closest well relative, but the result is harder to interpret, because a negative test in a well person does not rule out a fault the family may still carry.
Why the extra effort is worth it
In many Telangana families the relative with cancer is an older parent living in a district town. Bringing them in for a single blood sample can feel like a lot of trouble. It is usually worth it, because their one result can spare several younger relatives an unclear test.
Testing the wrong person first is not a mistake so much as a missed opportunity. It can usually be corrected later if the right relative becomes available.Working out the order
How the right starting person is chosen
A counsellor weighs up more than one factor before recommending who goes first.
Who is already affected
Someone with a cancer diagnosis, especially at a young age or an unusual site, is the strongest starting point. Their cancer is the reason the family is asking in the first place.
Strongest signals
- Cancer at an unusually young age
- Two separate cancers in one person
- Breast cancer in a man
Who had the youngest or most unusual diagnosis
If several relatives have had cancer, the one diagnosed youngest or with the rarest pattern often carries the clearest signal. A relative diagnosed late in life may have a cancer that arose by chance.
Who is reachable and willing
A theoretically ideal candidate who cannot be reached or declines is not useful. Practical availability genuinely matters, and a relative who lives abroad can often give a sample locally.
Who has a sample already stored
If an affected relative has died, a stored tissue block from an earlier surgery can sometimes still answer the question.
Not sure whether this applies to you?
Ask an oncologistIn the counselling room
How a counsellor actually reaches this decision
The family tree is drawn out
Every relative who was diagnosed, with what, and at roughly what age, on both sides of the family.
The strongest candidate is identified
Usually the youngest diagnosis, the rarest cancer, or the person with more than one cancer themselves.
Availability is checked
Whether that person is living, reachable and willing changes the practical starting point, even if they are the ideal one on paper.
A fallback plan is agreed
If the first choice is not possible, the next best relative is identified before testing begins, so nothing stalls.
The result is shared with the family
Once the first result is back, the counsellor explains who should be offered testing next. A family letter can carry the exact fault to those relatives.
Terms in this conversation
Words a counsellor will use when planning the order
- Index case
- The first person tested in the family, usually the one already diagnosed. Everyone else's test is compared against their result.
- Informative result
- A result clear enough to guide the rest of the family, whether it finds a fault or rules one out with confidence.
- Uninformative negative
- A negative result in a well relative that cannot rule out a fault, because the family's true status was never confirmed in someone affected.
- Youngest diagnosis
- The relative diagnosed earliest in life. Often the strongest single clue that an inherited fault may be present.
- Panel testing
- Testing many genes at once in the index case, used when it is not obvious in advance which gene might be involved.
- Availability
- Whether the ideal relative can actually be reached and is willing to test, which can change the practical starting point.
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Side by side
Testing the affected relative first, or a well relative first
Affected relative first
Well relative first
A positive result names the exact fault
A negative result does not rule anything out
A negative result usually closes the question
Leaves the family history unresolved either way
The preferred, most efficient order
Sometimes the only option available
Guides who else should test next
Gives limited guidance for other relatives
Being straight with you
What this page cannot tell you
It cannot tell you which specific relative to start with in your own family. That depends on exactly who has been diagnosed, at what age, and who is reachable, and it needs a counsellor working through your family tree in detail.
It cannot promise a clear answer either way
Even testing the best possible candidate does not always give a definite result. Some tests come back uncertain, and the family may still need to be watched on history alone while science catches up.
Who this does not apply to
If nobody in the family has had cancer at an unusually young age or in an unusual pattern, there may be no clear candidate to start with, and testing may not be recommended for anyone yet.
If you are not sure who in your family this points to, call the helpline and describe who has been diagnosed. Someone will help you work out the starting point.Commonly believed
Four things families assume about who goes first
"The person most worried should test first."
Worry does not decide the order. The relative most likely to carry a fault, usually the one already diagnosed, gives the most useful result for everyone.
"It doesn't matter who tests first, as long as someone does."
It matters a great deal. Testing a well relative first can produce a negative result that tells the family nothing definite, wasting the chance a more informative test would have given.
"The oldest relative is always the right one to start with."
Age is not the deciding factor. The relative diagnosed youngest, or with the rarest pattern, usually carries the clearer signal, whatever their age is now.
"If the affected relative has died, testing cannot start at all."
Stored tissue from an earlier surgery or biopsy can sometimes still be tested. It is always worth asking before assuming the option is closed.
Questions we are asked
Common questions about choosing who tests first
Why not just test the youngest, healthiest relative first?
A negative result in a well person does not rule out a fault the family may still carry. Testing the relative who already has cancer gives a far more informative answer.
What if the affected relative refuses to be tested?
Their choice has to be respected. Testing can move to the next best candidate, though the result will usually be less definite for the rest of the family.
Can more than one relative test at the same time?
Yes, if more than one relative has had cancer. A counsellor can advise whether testing them together adds useful information or whether one alone is enough to start.
Does it matter which side of the family the cancer is on?
Faults can come from either parent, so both sides of the family tree are considered. The strongest candidate can come from either side.
What if the only affected relative has already died?
Ask whether a tissue block from their surgery or biopsy was kept. If one exists, it can sometimes be tested even years later.
Is a panel test needed for the first person, or a specific gene?
Usually a broader panel, since it is not always obvious in advance which gene might be involved. The counsellor will recommend the right scope based on the family history.
How long does it take to identify the right person to start with?
Often a single counselling session is enough, once the family tree is drawn out. Reaching and arranging testing for that person can take longer.
Where do we start if we are not sure who in the family to approach?
Call the helpline and describe who has had cancer in the family and at what age. Someone will help you identify the right starting point and arrange counselling.
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
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
- Cancer Research UK — Inherited cancer genes and increased cancer risk
- NCCN — NCCN Guidelines: Detection, Prevention, and Risk Reduction
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
Cascade testing: how a result moves through a familyWhat happens once the starting result is inTesting a relative who has already had cancerMore detail on why this relative goes firstTesting a deceased relative through stored tissueWhat to do if the ideal candidate has diedA negative result: what it does and does not rule outWhy the order of testing changes what a result means
Talk to us
Not sure who in your family should test first?
Describe who has been diagnosed and at what age, and we will help you work out the right starting point. One helpline serves every CION centre.