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The PMS2 gene: a proofreader for your DNA | CION Cancer Clinics
PMS2 is one of the genes that checks your DNA each time a cell divides and fixes the copying mistakes it finds. An inherited fault in PMS2 is one cause of Lynch syndrome, which raises the risk of bowel and womb cancer. Of the Lynch genes, PMS2 carries the lowest risk. This page explains what the gene does, what a fault changes and what it does not. 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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The short answer
What does the PMS2 gene actually do?
PMS2 helps your cells fix spelling mistakes in their DNA. Every time a cell divides, it copies billions of DNA letters, and a few are copied wrongly. PMS2 is part of a small repair team that finds those errors and removes them before they become permanent.
Part of the mismatch repair team
Doctors call this team the mismatch repair system. It has four main genes: MLH1, MSH2, MSH6 and PMS2. They work in pairs. MSH2 and MSH6 spot the wrong letter. MLH1 and PMS2 then work together to cut it out so it can be replaced. An inherited fault in any one of the four causes Lynch syndrome.
Why a PMS2 fault is the mildest of the four
When PMS2 is missing, related proteins can take on part of its work. Repair slows rather than stopping. This is thought to be one reason PMS2 faults carry the lowest cancer risk of the Lynch genes, and why cancers in PMS2 families often appear later in life.
A PMS2 fault is not a cancer diagnosis. It is a raised risk that can be watched.Four things to know
What changes when PMS2 is faulty?
A fault changes less than most families fear. These are the four points that matter.
One working copy is still enough
You carry two copies of PMS2. With one faulty copy, the other keeps repair running normally in almost every cell. Trouble starts only if the working copy is also damaged in a single cell during life.
Errors build up in repeated stretches
DNA has stretches where a short pattern repeats, like a stutter. Without repair, these stretches change length. Laboratories measure this as microsatellite instability, or MSI, a sign that repair has failed inside a tumour.
Mainly the bowel and the womb
The cancers linked to PMS2 are mostly in the bowel and the womb lining. Links to other organs are weaker than for other Lynch genes, and studies are still settling them.
Where the risk sits
- Bowel (colorectal) cancer
- Womb lining (endometrial) cancer
- Other organs: less clear for PMS2
Two faulty copies is a different condition
A child who inherits a PMS2 fault from both parents has a rare childhood condition called constitutional mismatch repair deficiency. It is more likely when parents are related by blood.
This matters in families where marriage within the family is common.Not sure whether this applies to you?
Ask an oncologistFrom fault to tumour
How does a PMS2 fault lead to cancer?
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You inherit one faulty copy
Every cell in your body has one working PMS2 copy and one faulty copy from birth. Repair still works, and you feel nothing at all.
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The working copy is lost in one cell
Over many years, the working copy can be damaged in a single cell of the bowel or womb lining. That one cell now has no working PMS2.
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Mistakes start to stay in place
Each time that cell divides, copying errors are kept instead of fixed. Some of them land in genes that control growth.
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A polyp or abnormal area forms
In the bowel, this usually shows first as a polyp, a small growth on the lining. Polyps can be seen and removed during a colonoscopy before they turn into cancer.
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Which is why checks work
The slow gap between the first abnormal cells and a cancer gives surveillance time to act. That is the whole reason carriers are offered regular colonoscopies.
On your report
What do the words on a PMS2 report mean?
- Lynch syndrome
- An inherited condition caused by a fault in one of the mismatch repair genes. It raises the risk of bowel, womb and some other cancers.
- Mismatch repair (MMR)
- The cell's system for fixing copying mistakes in DNA. PMS2 is one of its four main genes.
- Heterozygous
- You have one faulty copy and one working copy. This is the usual situation in Lynch syndrome.
- Pathogenic variant
- A change in the gene known to stop it working. This is what a positive result means.
- Immunohistochemistry (IHC)
- A stain on tumour tissue showing which repair proteins are present. Loss of PMS2 alone points towards a PMS2 problem.
- Germline
- Present in every cell from birth, so it can be passed on. A fault found only in the tumour is called somatic.
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Side by side
How is PMS2 different from other Lynch genes?
PMS2
MLH1 and MSH2
Lowest cancer risk of the Lynch genes
Highest cancer risk of the Lynch genes
Cancers tend to appear later in life
Cancers can appear at younger ages
Mainly bowel and womb lining
A wider range of organs
Testing is technically harder
Testing is usually straightforward
Family history often looks mild
Family history is often striking
Commonly believed
What do families get wrong about PMS2?
"PMS2 is Lynch syndrome, so my risk is the same as my cousin's MLH1 result."
Each Lynch gene carries its own risk, and PMS2 is the mildest. Surveillance for PMS2 carriers is often lighter than for MLH1 or MSH2, though guidelines differ on the details.
"Nobody in our family had cancer young, so it cannot be PMS2."
PMS2 families often look ordinary. Cancers tend to come later and fewer relatives are affected. That is exactly why PMS2 is often found only when a relative's tumour is tested.
"My tumour lost PMS2, so I definitely have Lynch syndrome."
Not always. Loss of PMS2 on a tumour stain is a clue, not a diagnosis. The loss can come from changes inside the tumour alone. A blood test is needed to know whether the fault is inherited.
"A positive result means I need surgery."
Most PMS2 carriers are managed with regular checks. Preventive surgery on the womb and ovaries is one option some women discuss once their family is complete. It is a choice made with a specialist, never a requirement.
Being straight with you
What can this page not tell you?
It cannot tell you what your own PMS2 result means. The exact variant, how the laboratory classified it and your family history all change the picture. What your specific variant means is a question for the counsellor who ordered the test.
It cannot give you an exact risk
Risk estimates for PMS2 come from studies that are still fairly small, and they have moved as more families are studied. Early estimates were higher because they came from families with a lot of cancer. Your counsellor will use current guidance, not a figure from a website.
Who this does not apply to
Most people do not need a PMS2 test. If one older relative had bowel cancer and there is no pattern in the family, testing is unlikely to help. Tumour mutation testing to choose a cancer drug is a separate question, covered under targeted therapy.
Bring the report and a list of relatives with cancer to your first appointment. It makes the conversation far more useful.Questions we are asked
Common questions about the PMS2 gene
Is a PMS2 fault the same as Lynch syndrome?
A PMS2 fault is one of four gene causes of Lynch syndrome. So a PMS2 carrier does have Lynch syndrome, but a milder form than carriers of MLH1 or MSH2 faults. Many doctors now describe it by the gene, so that the care plan matches the actual risk.
Which cancers are linked to PMS2?
Mainly bowel cancer and cancer of the womb lining. The risk of these is raised above the general population but is lower than for other Lynch genes. Links to ovarian, stomach and urinary tract cancers are weak or unproven for PMS2, and research is still clarifying them.
Can I pass a PMS2 fault to my children?
Each child of a carrier has a one in two chance of inheriting it, and sons and daughters are equally likely to. A child who does not inherit the fault cannot pass it on. Their risk is the same as anyone else's in the general population.
How is PMS2 usually found in a family?
Often through the tumour of a relative with bowel or womb cancer. A stain on the tumour showed PMS2 was missing, and a blood test then confirmed an inherited fault. Sometimes it turns up on a wider gene panel ordered for another reason.
What if both parents carry a PMS2 fault?
Each child then has a one in four chance of inheriting both faults. Two faulty copies cause constitutional mismatch repair deficiency, which brings cancers in childhood and needs specialist care from early life. If both partners come from affected families, ask for counselling before planning a pregnancy.
Does a PMS2 fault change cancer treatment?
It can. Tumours with failed mismatch repair can respond to immunotherapy, and surgeons may weigh the fault when planning bowel surgery. These decisions depend on the tumour itself and are made by the treating oncologist, not from the gene result alone.
Why was I told PMS2 is hard to test?
PMS2 has a near copy elsewhere in the DNA, called a pseudogene. Standard tests can confuse the two, so laboratories need extra steps to check a result. A reliable laboratory confirms any finding in the affected region with a second method before reporting it.
Where do I start if a relative tested positive?
Ask your relative for a copy of their report showing the exact variant. Take it to a genetic counsellor or your oncologist, who can arrange a test for that one variant. Call the CION helpline if you are unsure 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)
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Sources
- MedlinePlus Genetics — PMS2 gene
- GeneReviews (NCBI) — Lynch Syndrome
- National Cancer Institute — Genetics of Colorectal Cancer (PDQ)
- MedlinePlus Genetics — Lynch syndrome
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.
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