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The POLE and POLD1 genes: what they do and why it matters | CION Cancer Clinics
POLE and POLD1 hold the instructions for two machines that copy your DNA every time a cell divides. Both have a proofreading step that catches copying mistakes. When an inherited fault switches off that proofreading, errors build up far faster than usual, and the bowel is where this most often leads to polyps and cancer. This page explains how that happens and why it matters. 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 do the POLE and POLD1 genes actually do?
- How are POLE and POLD1 different from each other?
- How does a proofreading fault turn into a cancer?
- The words you will meet, in plain language
- How is this different from Lynch syndrome?
- What this page cannot tell you
- What do people get wrong about these genes?
- Common questions about POLE and POLD1
The short answer
What do the POLE and POLD1 genes actually do?
They carry the instructions for two copying machines inside every cell. Each time a cell divides, its whole DNA must be copied, letter by letter. POLE and POLD1 make the machines that do most of that copying, and each one has a built-in proofreader that catches wrong letters as they go in.
Why the proofreading step matters
The body copies its DNA an enormous number of times over a lifetime. Even a tiny error rate adds up. The proofreading step removes most mistakes on the spot, before they become permanent. It is one of the main reasons the copying is so accurate.
What goes wrong in a carrier
An inherited fault in the proofreading part of either gene means the copier still works, but checks its own work badly. Errors slip through each time the cell divides. In tissues that renew quickly, like the lining of the bowel, those errors pile up fastest, which is why polyps tend to appear there first.
The copier still copies. What is lost is the checking.Two related genes
How are POLE and POLD1 different from each other?
The two genes do similar jobs on different halves of the DNA. Their risk patterns overlap but are not identical.
POLE
Makes the main copier for one strand of the DNA, called the leading strand. Faults here are the more often reported of the two.
Linked most with
- Bowel polyps and bowel cancer
- Polyps in the first part of the small bowel
- A few brain and other cancers in reported families
POLD1
Makes the copier for the other strand, called the lagging strand, which is copied in short pieces. Faults here are rarer still.
Linked most with
- Bowel polyps and bowel cancer
- Cancer of the womb in women
- Possibly breast cancer, on limited evidence
Only one part of each gene counts
Both genes are long. Only faults in the proofreading section, called the exonuclease domain, are known to raise cancer risk. A change elsewhere in the gene is a different finding and usually does not carry the same meaning.
Same gene, different conditions
Rare changes elsewhere in POLE and POLD1 cause unrelated conditions affecting growth, body fat or the immune system. They are not the same as the cancer risk described here.
Not sure whether this applies to you?
Ask an oncologistFrom fault to tumour
How does a proofreading fault turn into a cancer?
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You inherit one faulty copy
Everyone has two copies of each gene. A carrier is born with one working copy and one with broken proofreading, in every cell of the body.
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The faulty copier still does its share
Unlike many cancer genes, the faulty copy is not simply silent. It keeps copying DNA without checking, so errors start to slip in even though a working copy is also present.
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Some errors hit growth-control genes
Most errors land in parts of the DNA that do not matter. Occasionally one lands in a gene that tells the cell when to stop dividing. That cell grows faster than its neighbours and forms a small polyp.
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A polyp keeps gathering changes
Because the proofreading problem continues, a polyp keeps collecting errors. Over years, one may become a cancer. Removing polyps during colonoscopy breaks this chain.
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Tumours end up with unusually many changes
Cancers in carriers often carry far more gene changes than usual. Doctors call these tumours hypermutated or ultramutated, and it can affect how they respond to some treatments.
On your report
The words you will meet, in plain language
- DNA polymerase
- The copying machine that builds a new strand of DNA when a cell divides. POLE and POLD1 each make one part of a polymerase.
- Proofreading
- The copier checking its own work. A wrong letter is snipped out and replaced before the copier moves on.
- Exonuclease domain
- The part of the copier that does the checking. Faults here are the ones linked to cancer risk.
- Hypermutated tumour
- A tumour carrying far more gene changes than usual. It is a feature of the tumour, found by testing the tumour itself.
- Mismatch repair
- A second, separate checking system that fixes errors after copying. Faults in it cause Lynch syndrome, which is a different condition.
- Germline
- Present in every cell from birth, so it can be inherited. The opposite word is somatic, meaning a change found only in a tumour.
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Side by side
How is this different from Lynch syndrome?
POLE or POLD1 fault
Lynch syndrome
Checking during copying is lost
Repair after copying is lost
Standard tumour screening for Lynch usually looks normal
Tumour screening usually flags it
Several to many bowel polyps are common
Usually one or a few polyps
Womb cancer linked mainly to POLD1
Womb cancer is a major risk
Very few families described
Well studied across many countries
Being straight with you
What this page cannot tell you
It cannot tell you whether the change on your report is one that raises risk. That depends on exactly where in the gene it sits and how the laboratory classified it. What your specific variant means is a question for the counsellor who ordered the test.
It cannot explain a tumour-only result
POLE changes are often found in tumours, especially of the womb and bowel, in people who inherited nothing. That is a somatic finding. It can matter a great deal for treatment, and it is handled by your oncologist and the targeted therapy team, not through family testing.
Who this does not apply to
Most people with bowel polyps do not carry a POLE or POLD1 fault. These genes explain only a small share of families with many polyps. If no one in your family has had many polyps or early bowel or womb cancer, this test is unlikely to be relevant to you. Studies so far are small, and very few include Indian families.
Commonly believed
What do people get wrong about these genes?
"A fault anywhere in POLE means a high cancer risk."
Only faults in the proofreading section are known to raise risk. Many other changes in this long gene are harmless, or are linked to unrelated conditions. The exact position matters.
"My tumour was checked for Lynch syndrome and was normal, so nothing is inherited."
Standard Lynch screening of a tumour usually looks normal in POLE and POLD1 carriers. A normal result there does not rule these genes out. A blood test is needed.
"Proofreading faults only matter in old age."
Bowel cancers in carriers are often found younger than usual, sometimes in early adult life. That is why checks start earlier than routine screening.
"The faulty gene can be repaired."
An inherited fault is present in every cell and cannot be corrected or reversed. What can be changed is how early polyps are found and removed.
Questions we are asked
Common questions about POLE and POLD1
Is a POLE fault the same as PPAP?
Not quite. PPAP, or polymerase proofreading-associated polyposis, is the name of the condition. POLE and POLD1 are the two genes that cause it. A carrier of a proofreading fault in either gene is said to have PPAP, even before any polyp has appeared.
How is it inherited?
It is dominant. A carrier parent passes the fault to each child with a one in two chance, whether the child is a son or a daughter. Occasionally a fault arises for the first time in one person, with no family history behind it.
Why was my tumour called ultramutated?
Because a proofreading problem allowed many changes to pile up inside it. Tumours like this can also arise without any inherited fault, when the POLE change is present only in the tumour. Only a blood or saliva test can say whether it was inherited.
Does a POLE fault change cancer treatment?
It can. Tumours with very many gene changes are often more visible to the immune system, and immunotherapy has worked in some of them. Whether that applies to a particular cancer is decided by the oncologist, using tests on the tumour itself.
Which test finds a POLE or POLD1 fault?
Usually a blood or saliva test using a panel of genes linked to bowel polyps and bowel cancer. POLE and POLD1 are not on every panel, so ask your counsellor whether they are included before the sample is sent.
My report shows a POLE variant of uncertain significance. Is that the same?
No. It means the laboratory cannot yet say whether the change matters. It should not be used to plan surgery or to test relatives. Ask how you will be told if it is ever reclassified.
Are these faults more common in India?
Nobody knows yet. Almost all published families come from Europe and North America. Studies in Indian families are very limited, which is one reason your counsellor may be cautious about quoting figures from abroad.
Can lifestyle make a difference?
It cannot change the gene. Not smoking, keeping a healthy weight and eating plenty of fibre are sensible for everyone and support bowel health. They do not replace colonoscopy, which is the step that actually lowers risk for carriers.
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)
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Sources
- MedlinePlus Genetics — POLE gene
- MedlinePlus Genetics — POLD1 gene
- National Cancer Institute — Genetics of Colorectal Cancer (PDQ®)–Health Professional Version
- NCCN — Genetic/Familial High-Risk Assessment: Colorectal, Endometrial, and Gastric
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
POLE and POLD1: which cancers and what riskWhich organs are affected, and how firm the evidence isPolymerase proofreading-associated polyposisThe condition these genes cause, in fullPOLE or POLD1 positive: what happens nextThe first few months after a positive resultSurveillance for POLE and POLD1 carriersWhich checks carriers are offered, and when
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Was POLE or POLD1 mentioned on a report you were given?
Tell us what the report says and who in your family has had polyps or cancer. We will help you understand whether counselling or further testing makes sense. One helpline serves every CION centre.