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The APC gene: a brake on bowel cell growth | CION Cancer Clinics
APC is a gene that stops cells in the bowel lining from growing out of control. An inherited fault in APC causes familial adenomatous polyposis, where hundreds of polyps can form from the teenage years. This page explains what the gene does, how a fault leads to polyps and cancer, and why early, regular checks change what happens next. 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
- What does the APC gene actually do?
- Which conditions are linked to APC?
- How does an APC fault lead to bowel cancer?
- The words you will meet, in plain language
- Is an APC fault in the tumour the same as an inherited one?
- What families often get wrong about APC
- What this page cannot tell you
- Common questions about the APC gene
The short answer
What does the APC gene actually do?
APC is a gene that works as a brake on cell growth in the lining of the bowel. When both copies stop working in one cell, that cell can grow into a polyp, and a polyp can slowly turn into cancer. An inherited fault in APC means every cell starts life with one copy already broken.
A brake inside every bowel cell
The lining of the bowel renews itself constantly. Old cells are shed and new ones grow from below. APC keeps that growth orderly. It holds back a protein signal that tells cells to keep dividing, so the lining stays thin and even.
What happens when the brake fails
Without APC, that growth signal stays switched on. The cell keeps dividing and forms a small raised lump called an adenoma, a type of polyp. APC failure is one of the earliest steps in most bowel cancers, including the many that are not inherited at all.
Why an inherited fault matters so much
Someone born with one faulty copy needs only one more hit in any bowel cell for a polyp to start. Across the whole bowel, that happens again and again. This is why people with the inherited condition can grow hundreds or thousands of polyps.
An APC fault is not a cancer diagnosis. It is a reason to be watched closely and early.One gene, several patterns
Which conditions are linked to APC?
The same gene can produce quite different pictures. Where the fault sits inside the gene partly decides which one a family sees.
Classic FAP
Familial adenomatous polyposis, or FAP, means a very large number of polyps, usually starting in the teenage years. Without treatment, bowel cancer is expected by middle age. Surgery to remove the large bowel is usually planned before that happens.
Attenuated FAP
A milder form with fewer polyps that tend to appear later in life. Some people can be managed with regular colonoscopy and polyp removal for years before surgery is discussed.
Features outside the bowel
APC faults can also affect other parts of the body.
Can include
- Polyps in the stomach and the duodenum
- Desmoid tumours in the abdomen
- Extra teeth, bone lumps and harmless eye spots
- A raised risk of thyroid cancer
The low-risk variant
One specific APC change, called I1307K, only modestly raises bowel cancer risk and does not cause polyposis. It is common in some communities abroad and is often confused with FAP.
Not sure whether this applies to you?
Ask an oncologistFrom fault to polyp
How does an APC fault lead to bowel cancer?
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You inherit one faulty copy
Every cell carries two copies of APC. In an inherited fault, one copy is broken from birth. The other copy still works, so the bowel looks normal in early childhood.
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The second copy is lost in one cell
Ordinary copying errors knock out the working copy in a single bowel cell. Because the bowel lining has millions of dividing cells, this happens many times over.
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Polyps begin to form
Each of those cells can grow into an adenoma. In classic FAP, polyps usually become visible on colonoscopy in the teenage years.
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A polyp gathers further faults
Over years, one polyp may pick up more gene changes and become cancer. Any single polyp is unlikely to do so. With so many of them, the chance that one will is very high.
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Watching early breaks the chain
Regular colonoscopy finds polyps while they are still harmless. Well timed surgery removes the organ at risk before cancer appears.
On your report
The words you will meet, in plain language
- Adenoma
- A polyp made of gland cells. It is not cancer, but it is the kind of polyp that can become cancer if left for years.
- Polyposis
- Having many polyps rather than one or two. It is the defining feature of FAP.
- Germline variant
- A gene change present in every cell from birth, which can be passed to children. This vertical deals only with germline changes.
- Pathogenic
- Known to break the gene. A pathogenic APC variant confirms the inherited condition.
- De novo
- New in this person, not inherited from either parent. It can still be passed on to their children.
- Tumour suppressor
- A gene whose job is to stop cells growing out of control. APC is one of these.
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Two different tests
Is an APC fault in the tumour the same as an inherited one?
Inherited APC fault
APC fault only in the tumour
Found in a blood or saliva sample
Found only in tumour tissue
Present in every cell from birth
Arose in the bowel during life
Relatives can be tested for it
Relatives are not affected by it
Changes screening for the whole family
Very common in ordinary bowel cancer
Commonly believed
What families often get wrong about APC
"Nobody else in our family has polyps, so it cannot be inherited."
About one in four people with FAP are the first in their family. Their fault arose new. They can still pass it on to each child.
"Children are too young to worry about this."
FAP is one of the few conditions where testing in childhood is standard. Bowel checks usually begin in late childhood or the early teens, because polyps can start that young.
"Once the bowel is removed, the problem is over."
Surgery removes the biggest risk. Checks of the upper gut, the remaining rectum or pouch, and the thyroid still carry on for life.
"An APC change on my tumour report means my children are at risk."
Not necessarily. Many bowel cancers carry an APC fault that arose only in the tumour. Only a blood test for inherited faults can answer the family question.
Being straight with you
What this page cannot tell you
It cannot tell you what your own result means. The exact position of a fault inside APC, and how the laboratory has classified it, both change the advice. What your specific variant means is a question for the counsellor who ordered the test.
It cannot set your screening dates
When colonoscopy starts, how often it repeats and when surgery is discussed depend on how many polyps are found. A gastroenterologist and a genetic counsellor plan that together, and the plan changes as findings change.
Who this does not apply to
Most people with one or two polyps, or one relative with bowel cancer at an older age, do not have an APC fault and do not need this test. If your tumour report mentions APC, that is a question for the tumour testing team at targeted therapy, not proof of an inherited condition.
Questions we are asked
Common questions about the APC gene
Is FAP the same as bowel cancer?
No. FAP is an inherited condition that causes many polyps. Cancer develops only if those polyps are left in place for years. Regular checks and well timed surgery exist to stop that from happening, and they work well when started early.
What is the chance of passing an APC fault to my child?
Each child has a one in two chance of inheriting it, whichever parent carries the fault. Sons and daughters are affected equally. A child who does not inherit the fault cannot pass it on and needs only ordinary screening.
How is an APC fault found?
By a blood or saliva test that reads the gene. It is usually offered to someone with many polyps, or to relatives once a fault is known in the family. A genetic counsellor arranges it and explains the result.
Can the test miss an APC fault?
Sometimes. A few people with many polyps have no fault found in APC. Some have a fault in another gene, such as MUTYH. Others carry the fault in only some of their cells. Your counsellor will explain what a negative result means for you.
Does an APC fault affect organs other than the bowel?
It can. Polyps in the duodenum, desmoid tumours and thyroid cancer are the most important. Harmless features such as extra teeth, bone lumps and flat spots on the retina can also be clues that lead to diagnosis.
Is there a medicine that fixes the gene?
No medicine repairs an APC fault. Some drugs have been studied to reduce polyp numbers, but results are mixed and none replaces colonoscopy or surgery. Ask your specialist before taking anything for this reason.
Is testing covered by Aarogyasri or insurance?
Cover for genetic tests varies. Scheme packages usually fund treatment rather than predictive testing, and private policies differ. Ask the helpline to check your own cover before the sample is sent.
Where do I start if several relatives had polyps young?
Write down who had polyps or bowel cancer, and roughly at what age, on both sides. Bring that list and any colonoscopy reports to a genetic counsellor or your gastroenterologist. Call the CION helpline if you are unsure who to see.
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
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Sources
- GeneReviews (NCBI) — APC-Associated Polyposis Conditions
- MedlinePlus Genetics — APC gene
- MedlinePlus Genetics — Familial adenomatous polyposis
- 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 riskEvery organ an APC fault can affect, in one placeAPC positive: what happens nextThe first months after a positive resultAttenuated FAP and a milder APC resultWhen the polyp count is lower and laterTesting the family for APCWho should be tested, and at what stage of life
Talk to us
Has someone in your family been told they have many polyps?
Tell us what the colonoscopy found and who else in the family is affected. We will help you work out whether a genetic referral makes sense. One helpline serves every CION centre.