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FAP explained: the inherited condition behind hundreds of polyps | CION Cancer Clinics
Familial adenomatous polyposis, or FAP, is an inherited condition that makes the large bowel grow hundreds of small growths called polyps, usually from the teenage years. Left alone, those polyps almost always lead to bowel cancer. Found early, it is very manageable with regular checks and well-timed surgery. This page explains the gene behind it, how it passes down a family, and what care looks like over a lifetime. 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
- What is FAP, in plain words?
- Which parts of the body does FAP affect?
- What does care for FAP look like, step by step?
- The words you will meet, in plain language
- How is FAP different from ordinary bowel polyps?
- What this page cannot tell you
- Four things families tell us, and what is actually true
- Common questions about FAP
The short answer
What is FAP, in plain words?
FAP is an inherited condition caused by a fault in one gene, called APC. That gene normally acts as a brake on cell growth in the lining of the bowel. When one copy is faulty from birth, the bowel lining starts growing small lumps called polyps, usually from late childhood or the teenage years. By early adulthood there can be hundreds of them.
How it differs from an ordinary polyp
Many older adults have one or two polyps removed at a routine colonoscopy. That is common and is not FAP. In FAP the polyps are too many to remove one by one, they start young, and they keep coming. It is the sheer number that changes the plan.
Why doctors take it so seriously
Each polyp is small and harmless at first. With hundreds of them, the chance that one turns into cancer becomes very high. Left alone, classic FAP almost always leads to bowel cancer, often by early middle age. That is why it is found through screening and managed with planned surgery, long before cancer has a chance to start.
FAP is serious, and it is also one of the best understood inherited conditions. Families who are watched do far better than families who are not.More than the bowel
Which parts of the body does FAP affect?
The bowel is the main concern, but the APC fault is in every cell. That is why care for FAP reaches beyond one organ.
The large bowel
This is where the polyps grow in large numbers. Regular colonoscopy tracks them, and preventive surgery removes the part of the bowel where cancer would otherwise start.
The stomach and upper gut
Polyps also form in the stomach and in the first part of the small bowel, called the duodenum. These need their own camera test, which continues even after bowel surgery.
Outside the gut
Some people develop features elsewhere in the body.
- Desmoid tumours, firm growths in the belly wall or deeper
- A raised chance of thyroid cancer, mostly in young women
- Harmless bony lumps, skin cysts and extra teeth
- Flat dark spots at the back of the eye, which do no harm
Very young children
A rare liver tumour of early childhood, called hepatoblastoma, is more common in FAP families. Whether to check for it is a decision your team will talk through with you.
Not sure whether this applies to you?
Ask an oncologistOver a lifetime
What does care for FAP look like, step by step?
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The fault is confirmed in one family member
A blood test in the person with polyps finds the exact APC fault. Once it is known, every relative can be tested for that same fault simply and reliably.
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At-risk children are tested and checked
Children who carry the fault start bowel checks in late childhood or the early teens. Children who do not carry it are spared them completely.
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Surgery is planned, not rushed
When the polyps become too many to watch safely, the bowel surgeon plans an operation. Timing is usually chosen around school, exams and work.
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Checks continue after surgery
Whatever bowel remains, and the upper gut, are still checked with a camera. Thyroid scans and a watch for desmoid tumours are added as your team advises.
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The family is kept in the loop
Brothers, sisters, children and sometimes parents are offered testing. Each new child born into the family is offered it too, when the time is right.
On your report
The words you will meet, in plain language
- APC
- The gene behind FAP. Its job is to stop bowel lining cells from growing when they should not.
- Polyp
- A small lump growing from the inside wall of the bowel. Most start harmless. Some can slowly turn into cancer.
- Adenoma
- The type of polyp seen in FAP. It is the kind that can, over years, become a cancer if left in place.
- Colectomy
- An operation to remove the large bowel, fully or in part. In FAP it is usually done to prevent cancer before it starts.
- Attenuated FAP
- A milder form, with fewer polyps appearing later in life. It is still managed with regular checks.
- De novo
- A new fault that started with this person rather than coming from a parent. Their own children can still inherit it.
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Side by side
How is FAP different from ordinary bowel polyps?
FAP
Ordinary polyps
Hundreds of polyps, sometimes thousands
One or a handful at a time
Start in late childhood or the teens
Usually found in later adult life
Caused by an inherited APC fault
Build up with age, with no single gene behind them
Managed with planned preventive surgery
Removed during the colonoscopy itself
Relatives are offered a gene test
Relatives follow routine screening advice
Being straight with you
What this page cannot tell you
It cannot tell you whether you or your child has FAP. That is answered by a genetic test, arranged after a genetic counsellor or bowel specialist has looked at the colonoscopy findings and the family tree. It also cannot tell you when surgery should happen. That depends on how many polyps there are, how large they are, and what is happening in your life.
It cannot read your report for you
APC reports name an exact variant, and different variants can behave differently. What your specific variant means is a question for the counsellor who ordered the test. Please do not search the variant name online and draw conclusions alone.
Who this does not apply to
Most people who have had a polyp removed do not have FAP and do not need this test. If a routine colonoscopy in later life found one or two polyps, and nobody in the family had polyps young, this page is unlikely to be about you. Your doctor will tell you when your next routine check is due.
Counselling in Telugu can be arranged, and relatives from the districts can often be seen on the same visit.Commonly believed
Four things families tell us, and what is actually true
"No one in our family had bowel cancer, so it cannot be FAP."
A sizeable share of people with FAP are the first in their family to have it, because the fault started with them. Others come from families where earlier relatives died young of an illness that was never named.
"If there are no symptoms, the polyps can wait."
Polyps rarely cause symptoms until they are advanced. Bleeding, loose stools or tummy pain can appear late. Waiting for symptoms is exactly what screening is designed to avoid.
"Once the bowel is removed, FAP is finished."
Surgery removes the biggest risk, but the fault is still in every cell. The upper gut, any remaining rectum and the thyroid still need checking for life.
"Girls cannot pass it on, only boys."
Sons and daughters inherit FAP equally, and either parent can pass it on. Each child of a parent with FAP has a one in two chance of carrying the fault.
Questions we are asked
Common questions about FAP
Is FAP the same as bowel cancer?
No. FAP is a condition that makes bowel cancer very likely if nothing is done. Most people with FAP who are found through family screening never develop bowel cancer, because their polyps are watched and their bowel is removed at the right time. It is a risk to be managed.
Will my children get FAP?
Each child of a parent with FAP has a one in two chance of inheriting the fault, whether a son or a daughter. A simple blood test can tell which children carry it. Those who do not carry it cannot pass it on and need only routine screening.
When should my child be tested?
FAP is one of the few conditions where testing in childhood is usually advised, because bowel checks begin young and genuinely help. Most families test around the age screening would start. Your genetic counsellor will help you choose the timing and explain it to your child in words they can manage.
Can FAP appear when no one else in the family has it?
Yes. Some people are the first in their family to carry the fault, because it arose for the first time in them. Parents and siblings may still be offered a test to be sure. That person's own children can then inherit it in the usual way.
Does everyone with FAP need their bowel removed?
In classic FAP, surgery is almost always needed at some point, because the polyps become too many to control with colonoscopy. In the milder attenuated form, some people are managed with regular colonoscopy and polyp removal for many years. The decision is made with your bowel surgeon.
Is there a medicine that stops the polyps?
Some anti-inflammatory medicines have been studied and can reduce the number of polyps in some people. None of them replaces screening or surgery, and studies so far are small. Please do not start any of these on your own, because some carry real side effects.
Is FAP common in India?
FAP is rare everywhere and occurs in every population. Indian registry data are limited, so nobody can give a reliable local figure. What we do see is families diagnosed late, after a young relative has already developed cancer, which is why testing the wider family matters so much.
Where do we start if a relative has been diagnosed?
Ask for a copy of the relative's genetic report, or their colonoscopy findings if no test was done. Take it to a genetic counsellor or a bowel specialist. Call the CION helpline if you are not sure who to see, 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
- GeneReviews (NCBI) — APC-Associated Polyposis Conditions
- MedlinePlus Genetics — Familial adenomatous polyposis
- MedlinePlus Genetics — APC gene
- 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
Hundreds of polyps: what FAP actually looks likeWhat a colonoscopy in FAP shows, and why it changes the planWhen screening should start in an FAP familyThe age children begin bowel checks, and whyDeciding the timing of preventive bowel surgeryHow the operation is fitted around school, work and familyAttenuated FAP: a milder courseFewer polyps, appearing later, and what that changes
Talk to us
Has someone in your family been told they have FAP?
Tell us who was diagnosed and what their reports say. We will help you arrange genetic counselling and testing for the relatives who need it. One helpline serves every CION centre.