Medical Oncologist
CION Cancer Clinics
Testing a relative who has already had cancer | CION Cancer Clinics
The relative who has already had cancer is usually the best person to test first. Their result tells the rest of the family whether there is a gene fault to look for, and exactly which one. It can also change their own treatment. This page explains why they come first, how the test works, and what happens if they cannot or will not be tested. 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
- Why is the relative who had cancer tested first?
- Which relative with cancer should be tested?
- What happens when the affected relative agrees to test?
- What the words on this kind of report mean
- What each result means for the rest of the family
- What this page cannot tell you
- Four things families assume, and what is actually true
- Common questions about testing a relative who had cancer
The short answer
Why is the relative who had cancer tested first?
Because their result tells the rest of the family what to look for. If a gene fault is driving the cancer in a family, the person who actually had cancer is the one most likely to carry it. Testing them first turns a vague worry into a specific question that relatives can answer with a simple, focused test.
What a well relative's test cannot do alone
If a healthy sister is tested first and nothing is found, the family is left guessing. She may simply not have inherited a fault that is there. Or there may be no fault at all. Nobody can tell which, because nobody knows what the family's fault looks like.
It can help the patient too
For some cancers, an inherited fault changes treatment. It can open up certain targeted medicines, or change the surgery a surgeon suggests. So the test is not only a favour to the family. It can matter to the person being tested, sometimes while they are still being treated.
This page is about inherited, or germline, testing. Testing the tumour itself for treatment choices is a separate test, covered under targeted therapy.Choosing the right person
Which relative with cancer should be tested?
When more than one person in the family has had cancer, the counsellor chooses carefully. The choice affects how useful the answer is.
The youngest at diagnosis
Cancer at an unusually young age is one of the strongest signs of an inherited cause. The relative diagnosed youngest is often the best first choice.
The one with the telling cancer
Some cancers point more clearly to an inherited cause than others. Ovarian cancer, breast cancer in a man, or two separate cancers in one person often carry more weight.
Often chosen first
- Two separate cancers in one person
- A rare cancer for their age or sex
- A cancer that fits the family pattern
The one who is willing and able
The ideal person on paper may be too unwell, too far away or not ready. A willing relative with a slightly weaker case is still far better than no test at all.
A relative who has died
If every affected relative has passed away, a tissue block kept by the hospital from an old surgery can sometimes still be tested. This is slower and not always possible.
Not sure whether this applies to you?
Ask an oncologistFrom referral to result
What happens when the affected relative agrees to test?
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A counselling conversation first
A genetic counsellor draws the family tree, explains what the test can and cannot show, and talks through what a result would mean for the patient and for relatives. Consent is always theirs to give.
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A blood or saliva sample
For most people a single blood sample is enough. If they have a blood cancer, or have had a bone marrow transplant, the laboratory may ask for a different sample, such as a small piece of skin.
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A panel of genes is checked
The laboratory looks across a group of genes linked to the cancers in the family. Because nobody knows yet which gene matters, a wider search makes sense at this stage.
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The result comes back to the counsellor
The report goes to the doctor or counsellor who ordered it. They explain it to the patient first, and help decide how and when the rest of the family is told.
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Relatives get a narrower, simpler test
If a fault is found, relatives are tested only for that one exact fault. That test is more focused and usually cheaper than the first one.
On the report
What the words on this kind of report mean
- Affected relative
- A family member who has had cancer. Counsellors also call this person the index case or the proband.
- Germline test
- A test for faults present in every cell from birth, which can be passed on. It is done on blood or saliva, not on the tumour.
- Panel
- A test that checks several genes at once. It is used first, when the family's fault is still unknown.
- Pathogenic variant
- A change in a gene known to raise cancer risk. This is what people mean by a positive result or a gene fault.
- Uninformative negative
- No fault found in someone who has had cancer. It does not rule out an inherited cause. It means none was found in the genes checked.
- Targeted family test
- A test for one known fault only, offered to relatives once the affected person's result is known.
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Side by side
What each result means for the rest of the family
A fault is found
No fault is found
Relatives can take a simple test for that one fault
Testing well relatives usually adds little
Relatives who test negative return to routine screening
Screening is planned from the family history instead
The patient's own treatment may change
Treatment is planned on the tumour itself
Carriers are offered closer checks
The file stays open as testing improves
Being straight with you
What this page cannot tell you
It cannot tell you which relative in your family should be tested, or whether your family needs testing at all. That depends on who was diagnosed, with what, and at what age. A genetic counsellor works that out from a full family tree on both sides.
It cannot read a result you already have
What a specific variant means is a question for the counsellor who ordered the test. The same gene name can carry very different meanings depending on the exact change and how it is classified.
Who this does not suit
Most families with one older relative who had a common cancer do not need this test. It is also not a tool to pressure someone who is unwell. A patient in the middle of treatment may not be ready, and that choice deserves respect. The counsellor can talk to them when the time is right.
Commonly believed
Four things families assume, and what is actually true
"He already has cancer, so testing him is pointless."
His result is the most useful one in the family. It can guide his own treatment and tell every relative exactly what to test for.
"She tested negative, so none of us can carry anything."
A negative result in someone with cancer is reassuring but not final. The cancer may have another cause, or the fault may be in a gene the panel did not check.
"It is quicker if the healthy children just test themselves."
Without the patient's result, a negative test in a child answers very little. Starting with the patient saves time and money across the whole family.
"Asking a sick relative to test is cruel."
Many patients are glad to do something that protects their children. The request should come gently, from a counsellor, and refusing is always allowed.
Questions we are asked
Common questions about testing a relative who had cancer
Can my mother be tested while she is on chemotherapy?
Usually, yes. An inherited test looks at genes present from birth, and treatment does not change them. A normal blood sample is often fine. Her oncologist and the counsellor will pick a sensible moment, so the test does not add strain during a hard stretch.
What if my relative has a blood cancer?
Blood may contain cancer cells, which can confuse an inherited test. The laboratory may ask for a small skin sample or another tissue instead. The same applies after a bone marrow transplant. The counsellor will arrange the right sample.
My father refuses to be tested. What can we do?
His choice stands. Relatives can still see a counsellor, who will assess their own risk from the family history. Sometimes testing a well relative is still worth doing, but the result will be harder to read. The counsellor will explain what it can and cannot tell you.
The relative who had cancer has died. Is it too late?
Not always. Hospitals often keep tissue blocks from surgery or biopsy, and these can sometimes be tested. Another affected relative may also be available. If neither works, the counsellor plans care from the family history.
Does a negative result in the patient mean we are safe?
It lowers the chance of a single inherited fault, but does not rule one out. Relatives with a strong family history may still need earlier or closer screening. Ask the counsellor how the negative result changes the plan for each person.
Is the patient's test the same as tumour testing?
No. Tumour testing looks at faults inside the cancer to choose medicines. An inherited test looks at faults present in every cell. Sometimes a tumour test hints at an inherited fault, and then a separate blood test is needed to confirm it.
Who pays for the affected relative's test?
It varies. Some insurance policies and some government schemes may help when the result affects treatment. Many families pay themselves. Ask the counsellor for the cost before the sample is taken, and ask how much the later family tests will cost.
Who tells the rest of the family the result?
Usually the patient, with help. Counsellors can give a family letter that explains the result in plain words, so relatives can take it to their own doctor. Nobody is told without the patient's agreement.
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
- National Cancer Institute — Cancer Genetics Risk Assessment and Counseling (PDQ) – Health Professional Version
- NHS — Predictive genetic tests for cancer risk genes
- MedlinePlus Genetics — What do the results of genetic tests mean?
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 mattersHow the counsellor chooses the starting pointTesting a relative who has never had cancerWhat changes when the tested person is wellTesting a deceased relative through stored tissueWhen the affected relative has passed awayHow cascade testing worksHow one result moves through the whole family
Talk to us
Is the right person in your family being tested first?
Tell us who in your family has had cancer and at what age. A counsellor will help you work out who should be tested first, and arrange it if it is needed. One helpline serves every CION centre.