Medical Oncologist
CION Cancer Clinics
APC in the family: who to test, and when | CION Cancer Clinics
Once an APC fault is found, parents, brothers, sisters and children should each be offered a test for that exact fault. Each has a one in two chance of carrying it. Unlike most inherited cancer faults, APC testing is usually offered to children, because bowel polyps can start young. This page explains who to test, in what order, and what each result changes. At CION Cancer Clinics, our oncologists explain what a gene result means for you and your family, and plan the checks that follow.
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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 once an APC fault is found?
- Which relatives need a test, and when?
- How does testing the family actually work?
- The words you will hear, in plain language
- What happens after a relative is tested?
- What this page cannot tell you
- Four things families tell us, and what is actually true
- Common questions about testing the family for APC
The short answer
Who in the family should be tested once an APC fault is found?
Parents, brothers, sisters and children of the person with the fault should be offered a test first. Each of them has a one in two chance of carrying the same fault. Once they know, those who carry it start regular checks, and those who do not can stop worrying about FAP.
Why APC family testing matters more than most
In FAP, bowel polyps can start in the teenage years and cancer can follow early. A relative who carries the fault and is not being watched is at real risk. A simple blood test for the known family fault tells each person where they stand.
Why a negative result is so useful
A relative who does not carry the known fault does not need the frequent colonoscopies an FAP family needs. They go back to the ordinary screening for their age. For children, that means no scopes from the teenage years and no years of waiting to see whether polyps appear.
The step that has to come first
Relatives can only be tested reliably once the exact fault in the family is known. That usually means the person with FAP or polyps is tested first, and their result is shared with everyone else.
One family test result can save a relative from years of unnecessary scopes, or catch polyps before they turn.Relative by relative
Which relatives need a test, and when?
The closest relatives come first. Each one decides for themselves, except young children, where parents decide with the doctor.
Brothers and sisters
Each has a one in two chance of carrying the fault if a parent carries it. Adult siblings should be offered a test soon, because polyps may already be present. A positive sibling needs a colonoscopy without delay.
Children
Unlike most inherited cancer faults, APC testing is usually offered in childhood. The timing is chosen so the answer is known before colonoscopy would need to begin.
Usually timed
- Before the teenage years, for classic FAP families
- Sometimes earlier, if liver checks in infancy are planned
- Later, in some attenuated FAP families
Parents
Testing parents shows which side the fault came from. If neither parent carries it, the fault probably arose new in the person with FAP, and the wider family is unlikely to be affected.
Aunts, uncles and cousins
Once you know which side the fault came from, relatives on that side can be offered a test too. Families from one village or community often stay in touch, which makes passing the news along easier.
Not sure whether this applies to you?
Ask an oncologistStep by step
How does testing the family actually work?
The first person is tested
Usually the person with FAP or many polyps. Their full APC test finds the exact fault that the rest of the family will be checked for.
A family letter is written
The counsellor gives a letter naming the fault and the laboratory that found it. Relatives take this to their own doctor or counsellor, wherever they live.
Each relative has counselling
Before testing, each relative talks through what a positive or negative result would mean for them. Parents do this on behalf of young children.
A targeted test is done
The laboratory looks only for the known family fault. This is simpler and usually cheaper than the first full test, and it needs only a blood or saliva sample.
A plan follows each result
Carriers are referred for colonoscopy and the checks that go with it. Those who test negative are told plainly that FAP checks are not needed.
On your report
The words you will hear, in plain language
- Cascade testing
- Testing relatives one circle at a time, starting with the closest, once a fault is found in the family.
- Predictive test
- A test in someone who is well, to find out whether they carry the family fault before any illness appears.
- Familial variant
- The exact fault found in your family. Relatives are tested for this one change, not for the whole gene again.
- De novo
- A fault that arose new in one person and was not inherited from either parent. Their children can still inherit it.
- Mosaicism
- When a new fault is present in only some of a person's cells. It can make a parent's test look negative when the fault is actually there.
- Carrier
- Someone who has the fault. In FAP, a carrier needs regular checks even when they feel completely well.
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Side by side
What happens after a relative is tested?
Carries the family fault
Does not carry it
Regular colonoscopy, often from the teenage years
Ordinary bowel screening for their age
Upper gut and thyroid checks added in adulthood
No extra checks for FAP
Surgery planned when polyps require it
No preventive surgery
Their own children can be tested
Their children cannot inherit the fault from them
Being straight with you
What this page cannot tell you
It cannot tell you which relatives in your family need testing first. That depends on who has had polyps, who is already being watched, and the exact fault found. A genetic counsellor draws the family tree and sets the order. What your specific variant means is a question for the counsellor who ordered the test.
When no fault is found in the family
Sometimes a person clearly has many polyps but no APC fault is found. Relatives then cannot be given a clean negative by testing. They are advised on colonoscopy from the family history instead. Another gene, such as MUTYH, may also be checked.
Who this does not apply to
If your report shows the APC I1307K variant, this page does not fit your family. That variant carries only a small extra risk, and relatives are usually advised differently. Relatives of someone with a single bowel polyp do not need APC testing at all. A counsellor will say honestly if testing is not needed.
Families across Telangana travel for these tests. Ask whether several relatives can be seen on one day.Commonly believed
Four things families tell us, and what is actually true
"My son has no symptoms, so he does not need testing yet."
Polyps in FAP grow silently for years. By the time there is bleeding or pain, they may already have turned. Testing and checks are done precisely because symptoms come late.
"Only the children who look like the affected parent will carry it."
Which child inherits the fault is chance, like a coin toss for each one. Looks, gender and birth order make no difference. Every child needs their own test.
"If I test negative, my children still need scopes."
If you do not carry the known family fault, you cannot pass it on. Your children do not need FAP checks because of your side of the family.
"Telling relatives will ruin marriage prospects."
This fear is real and common. But a relative who tests negative is free of the worry entirely, and a carrier who is watched has a far better outlook than one who is not. How and when to tell is something your counsellor can help you plan.
Questions we are asked
Common questions about testing the family for APC
At what age should children in an FAP family be tested?
Usually before the teenage years, so the result is known before colonoscopy would start. Some specialists test earlier if they plan liver checks in infancy. In attenuated FAP families testing may wait longer. Your counsellor will suggest the right time for your family.
Can a relative be tested if the affected person has died?
Sometimes. A stored tissue block from their old surgery can occasionally be tested. If that is not possible, a living relative with polyps may be tested instead. Failing that, relatives are advised on colonoscopy from the family history.
Do relatives need the full gene test again?
No. Once the family fault is known, relatives are tested for that one change only. This targeted test is simpler, and it usually costs less. Bring the family letter so the laboratory knows exactly what to look for.
My sibling tested negative but has polyps. Why?
Ordinary polyps are common in adults and are not caused by the family fault. A negative result still means your sibling does not have FAP. Their polyps are managed like anyone else's, and the specialist will set a schedule for follow-up scopes.
Neither parent carries the fault. Are my siblings safe?
Their risk is much lower, because the fault probably arose new in you. But a parent can occasionally carry it in only some cells, which a blood test can miss. Your counsellor may still suggest a baseline check for siblings to be sure.
Is family testing covered by insurance or government schemes?
Cover varies. Most private policies do not pay for predictive tests in well relatives, and scheme coverage under Aarogyasri or Ayushman Bharat depends on the listed package. Ask the counsellor's office for a written estimate before the test.
Can we avoid passing the fault to future children?
There are options, including testing during pregnancy and testing embryos during IVF. Each has costs and personal questions attached. Your counsellor can explain them without pressure, and there is a separate page on APC and family planning.
How do I start testing my family at CION?
Bring the report of the family member who tested positive, or their family letter. A counsellor will draw the family tree and arrange tests in the right order. Call the CION helpline to book, and ask for counselling in Telugu if you prefer.
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
- GeneReviews (NCBI) — APC-Associated Polyposis Conditions
- MedlinePlus Genetics — Familial adenomatous polyposis
- NHS — Predictive genetic tests for cancer risk genes
- National Cancer Institute — Genetics of Colorectal Cancer (PDQ)
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
APC mutation: which cancers and what riskWhat a carrier relative is actually at risk ofSurveillance for APC carriersThe checks a positive relative will startAPC and family planningOptions for couples who want to avoid passing it onAPC testing cost in HyderabadWhat the first test and relative tests cost
Talk to us
Need to arrange APC testing for your family?
Bring the family letter or report, and we will help plan who to test first and group relatives into one visit where possible. One helpline serves every CION centre.