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Testing the parents after a child tests positive | CION Cancer Clinics
When a child tests positive for an inherited cancer gene fault, the next step is usually to test both parents for that same fault. It tells the family whether the fault came from one side or arose new in the child. That answer decides who else needs testing, whether a parent needs checks of their own, and what it means for a future pregnancy. At CION Cancer Clinics, our oncologists plan screening and care for families with an inherited cancer syndrome, explained in plain words.
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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 are the parents tested after a child tests positive?
- What can the parents' results show?
- How are the parents tested?
- What do the words on a parent's report mean?
- What does each answer change for the family?
- What this page cannot tell you
- Four things parents tell us, and what is actually true
- Common questions about testing the parents
The short answer
Why are the parents tested after a child tests positive?
Because the child's result tells you the fault is there, but not where it came from. Testing both parents for that exact fault answers the next question. Did it come from the mother, from the father, or did it start fresh in the child? Each answer sends the family down a different path.
Why the answer matters to the parents themselves
A parent who carries the fault has a raised risk of their own, much like the child. Many carrier parents feel completely well and have never had cancer. Knowing lets that parent start their own checks, often long before any problem would have shown itself.
Why it matters to everyone else
Once you know which side the fault came from, you know which grandparents, aunts, uncles and cousins should be offered testing. The other side of the family can usually stop worrying. Without the parents' results, both sides are left guessing, sometimes for years.
Testing the parents is about planning, not blame. Nobody chooses the genes they pass on.Four possible answers
What can the parents' results show?
Most families land in one of the first two groups. The other two are less common, and a counsellor will explain them if they apply to you.
One parent carries the fault
The fault was inherited from that parent. For most childhood syndromes, each brother or sister of the child then has an even, one in two chance of carrying it too.
What usually follows
- Regular checks for the carrier parent
- Testing offered to that parent's relatives
- Testing discussed for the child's brothers and sisters
Neither parent carries it
The fault most likely arose new in the child, at or around conception. This is called de novo, and in some syndromes it is common. The parents' own risk is not raised, and their relatives do not need testing for this fault.
A small chance of it happening again in a later pregnancy still remains.Both parents carry a fault
A few childhood syndromes need a faulty copy from each parent. Each parent is then a carrier, and sometimes that carries an adult cancer risk of its own. This is more likely when parents are related by blood, as in the cousin and uncle-niece marriages still common in parts of South India.
The answer is not clear
Sometimes a parent carries the fault in only some of their cells, so a blood test can miss it or show it faintly. A second type of sample may be needed, and a counsellor will explain what the result can and cannot say.
Not sure whether this applies to you?
Ask an oncologistWhat actually happens
How are the parents tested?
A counselling session first
Both parents usually meet the counsellor together, though either can also be seen alone. The counsellor explains what each result would mean before anyone gives a sample, and takes consent from each parent separately.
A blood or saliva sample
Each parent gives a small blood sample, or sometimes saliva. No fasting is needed. Families travelling from a district can often give samples on the same day as the child's appointment.
A targeted test, not a full panel
The laboratory already knows the exact fault it is looking for, because it was found in the child. It checks only that one spot, which is usually quicker and cheaper than the child's original test.
Results in a second session
Results are explained in person or on a video call, never sent as a bare report on WhatsApp. A parent can ask to hear their own result privately first if they prefer.
On the report
What do the words on a parent's report mean?
- De novo
- A fault that is new in the child and was not inherited from either parent. The child can still pass it on to their own children later.
- Parental mosaicism
- A parent carries the fault in only some of their cells, sometimes including egg or sperm cells, without it showing clearly in blood.
- Targeted test
- A test that looks at one known spot in one gene, rather than scanning many genes. Also called a known-variant or single-site test.
- Cascade testing
- Offering testing step by step to relatives, starting with the closest and moving outward, once the family fault is known.
- Carrier
- Someone who has the fault but may never develop cancer. A carrier parent is not a patient, though they may need regular checks.
- Biallelic
- Having a faulty copy of the same gene from both parents. A few childhood syndromes need this, and each parent then carries one copy.
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Side by side
What does each answer change for the family?
A parent carries the fault
Neither parent carries it
That parent is offered regular checks of their own
Neither parent needs extra checks for this fault
Relatives on that side are offered testing
Relatives on both sides can usually be reassured
Each brother or sister has an even chance of carrying it
Brothers and sisters have a low chance, though testing may still be offered
A future pregnancy carries the same even chance
A future pregnancy carries a small but real chance
Being straight with you
What this page cannot tell you
It cannot tell you what your family's result means. The same gene can behave differently depending on the exact variant, and whether a carrier parent needs checks depends on that detail. What your specific variant means is a question for the counsellor who ordered the test.
It cannot tell you how to feel about the answer
A parent who turns out to be the source often takes the news hard, and the other parent may feel a relief they are ashamed of. Both reactions are ordinary. A counsellor can see each parent alone, and a psycho-oncologist can help if the feelings do not settle.
Who this does not apply to
Parents whose child's result showed only a variant of uncertain significance usually do not need testing, because there is nothing firm to look for. The same is true when a fault was found only in the tumour and not in the child's blood. That is tumour testing, which answers a different question about treatment, not about the family.
Commonly believed
Four things parents tell us, and what is actually true
"It must have come from the mother's side."
A fault can come from either parent, and fathers pass these faults on exactly as often as mothers do. In many families the blame falls on the mother before any test is done. Only the test can answer it, and often the answer is neither parent.
"My husband is healthy, so he cannot be the carrier."
Many carriers never develop cancer, or develop it only in later life. A parent can feel perfectly well, know of no cancer in their family, and still carry the fault. Health is not a test result.
"If neither of us has it, our next baby is safe."
The chance is much lower, but it is not zero. A parent can carry the fault in some egg or sperm cells without it showing in blood. Your counsellor can explain the options if you plan another pregnancy.
"Testing us will only start fights in the family."
It can stir up hard feelings, and counsellors are used to helping with that. But it also frees half the family from worry. Without it, relatives on both sides stay uncertain, and some may be screened for nothing.
Questions we are asked
Common questions about testing the parents
Do both parents need to be tested?
Ideally, yes. Testing only one parent can leave the question half answered. If the tested parent is negative, the fault may have come from the other parent or may be new in the child. Testing both gives a clear answer and tells you which side of the family to focus on.
What if one parent refuses or is not available?
Testing one parent still helps. If that parent carries the fault, the question is answered. If not, the other side stays uncertain, and relatives there may be offered testing directly instead. A counsellor can help you work out who to approach and how to raise it with them.
My child's father has died. Can he still be tested?
Sometimes. A stored tissue block from a past surgery or biopsy can occasionally be tested. If nothing was stored, testing his parents or his brothers and sisters can sometimes answer the question indirectly. Your counsellor will tell you which of these is realistic in your family.
Should the grandparents be tested too?
Only once you know which side the fault came from. When a parent tests positive, that parent's own mother and father are usually the next people offered testing, followed by that parent's brothers and sisters. The other side of the family normally does not need it.
Can testing reveal something else about our family?
Occasionally, testing both parents shows that a biological relationship is not what the family understood. Counsellors raise this possibility privately before testing, and any finding like this is handled in confidence. It is one reason each parent gives consent separately.
How long does a parent's result take?
A targeted test for a known fault is usually quicker than the child's original test, often a few weeks rather than longer. The laboratory gives a timeline when the sample is sent. Ask the counsellor how you will be told if there is a delay.
Will a parent's result affect health insurance?
India has no dedicated law on genetic discrimination in insurance, and the position is not settled. Some families prefer to arrange cover before a parent is tested. It is a fair question to raise at the first counselling session, not after the result, so you can decide with full information.
Where do we start?
Ask the team that tested your child to arrange a counselling session for both parents. Bring your child's report and a rough family tree covering both sides. If you are not sure who to approach, call the CION helpline and someone will point you to the right clinic.
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
- MedlinePlus Genetics — What are the different ways a genetic condition can be inherited?
- MedlinePlus Genetics — What is mosaicism?
- NHS — Predictive genetic tests 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
Should healthy siblings be tested?The next question once you know which parent carries itParental guilt after an inherited diagnosisFor the parent who turns out to be the sourceGenetic testing after a child's cancer diagnosisHow the child's own test was chosen and readWhen a childhood cancer suggests an inherited causeThe signs that start the whole process
Talk to us
Need both parents tested after your child's result?
Tell us what your child's report found. We will arrange counselling for both parents and explain what each result would mean before anyone is tested. One helpline serves every CION centre.