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MLH1 mutation: which cancers it affects and how much | CION Cancer Clinics
An inherited MLH1 fault mainly raises the risk of bowel cancer and, in women, cancer of the womb lining. Smaller raised risks affect the ovaries, stomach, small bowel, urinary tract and a few other organs. This page explains where the risk sits, why it is not one fixed number, and what checks are usually offered to bring it down. 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
- Which cancers does an MLH1 fault raise the risk of?
- Where the risk sits in the body
- How an MLH1 fault turns into bowel cancer, and where it can be stopped
- The words you will meet, in plain language
- Each risk, and what is usually offered for it
- Four things families tell us, and what is actually true
- What this page cannot tell you
- Common questions about MLH1 cancer risk
The short answer
Which cancers does an MLH1 fault raise the risk of?
An inherited MLH1 fault mainly raises the risk of bowel cancer and, in women, cancer of the womb lining. It also raises the risk of several other cancers by smaller amounts. MLH1 is one of the Lynch syndrome genes, and among them it carries some of the highest risks.
Raised risk, not certainty
Many carriers never develop cancer. Those who do often develop it at a younger age than usual, which is why checks start early. The good news is that bowel cancer in Lynch syndrome can often be prevented, because colonoscopy finds and removes growths before they turn into cancer.
Why this page does not quote one number
Published lifetime risk figures for MLH1 differ from study to study. They depend on who was studied, at what age, and whether they were having regular checks. Your counsellor will give you figures for your own gene, sex and family, from the source they trust most.
Risk figures describe large groups of carriers. They cannot tell you what will happen to one person.Organ by organ
Where the risk sits in the body
The risks are not spread evenly. Two organs carry most of it, and the rest are raised by much less.
Bowel
The largest risk for both men and women. Cancers often start in the right side of the colon and can appear younger than usual. Regular colonoscopy lowers this risk substantially.
Womb and ovaries
For women, the risk of cancer of the womb lining is about as high as the bowel risk. Ovarian cancer risk is raised too, but by a smaller amount.
Signs to report
- Bleeding between periods
- Any bleeding after menopause
Stomach and small bowel
Both risks are raised above the general population, though far below the bowel risk. Stomach risk may matter more in families where stomach cancer has already appeared.
Other organs
Smaller raised risks are reported for several other sites. For each of these, the evidence is thinner and checks are not routine.
- Kidney drainage tubes and bladder
- Pancreas and bile ducts
- Brain
- Skin glands that make oil
Not sure whether this applies to you?
Ask an oncologistWhere checks step in
How an MLH1 fault turns into bowel cancer, and where it can be stopped
-
A repair system is weakened from birth
MLH1 helps fix copying mistakes when cells divide. A carrier has one working copy instead of two, which is still enough for most cells.
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One bowel cell loses its second copy
Over time, the working copy can be damaged in a single cell. That cell can no longer fix its copying mistakes, and errors pile up quickly.
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A small growth, called a polyp, forms
The cell divides into a small growth on the bowel lining. It is not cancer yet, and it usually causes no symptoms at all.
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The polyp can change faster than usual
In Lynch syndrome a polyp can turn into cancer more quickly than in other people. This is why colonoscopy is repeated more often.
-
Colonoscopy removes it before that happens
A polyp found on colonoscopy is usually removed during the same test. That single step is what lowers bowel cancer risk for carriers.
On your report
The words you will meet, in plain language
- Lynch syndrome
- The inherited condition caused by a fault in MLH1 or one of several related repair genes.
- Mismatch repair
- The cell's system for correcting spelling mistakes made when DNA is copied. MLH1 is one of its main parts.
- Lifetime risk
- The chance of developing a cancer by an older age. It is an average across many carriers, not a forecast for you.
- Penetrance
- How often carriers actually develop cancer. For MLH1 it is high, but it is never all carriers.
- Microsatellite instability
- A pattern of errors seen in tumours that have lost mismatch repair. It is often the first clue that Lynch syndrome is present.
- Pathogenic variant
- A spelling change known to break the gene. This is the result that counts as positive for Lynch syndrome.
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Side by side
Each risk, and what is usually offered for it
Organ at risk
What is usually offered
Bowel
Regular colonoscopy, starting young
Womb lining
Prompt checks for unusual bleeding, and a talk about preventive surgery
Ovaries
Discussed together with the womb, once a family is complete
Stomach
A test for stomach infection, and endoscopy in some families
Urinary tract and others
Awareness of symptoms; routine checks are not proven
Commonly believed
Four things families tell us, and what is actually true
"Lynch syndrome is only about bowel cancer."
For women with an MLH1 fault, the risk to the womb lining is about as large as the bowel risk. Several other organs are affected too, though by less.
"All Lynch genes carry the same risk."
They do not. MLH1 and MSH2 carry the higher risks. MSH6 and PMS2 carry lower ones. This is why the exact gene on your report matters.
"If I have no symptoms, my bowel is fine."
Polyps and early cancers rarely cause symptoms. A colonoscopy finds them long before you would notice anything, which is why carriers are not told to wait for symptoms.
"Men do not need to worry about MLH1."
Men carry the full bowel risk, plus raised risks of stomach and urinary tract cancer. They also pass the fault to sons and daughters equally.
Being straight with you
What this page cannot tell you
It cannot give you your own risk. That depends on your exact variant, your sex, your age, your family history, and whether you have regular checks. Most large studies of MLH1 carriers come from Europe, America and Australia. Indian data are limited, so figures from abroad may not fit Indian families exactly.
It cannot interpret your result
What your specific variant means is a question for the counsellor who ordered the test. An uncertain result is not a Lynch diagnosis. A tumour that has lost MLH1 is not a Lynch diagnosis on its own either, because the gene can be switched off inside the tumour for other reasons.
Who this does not apply to
Most people with bowel cancer do not have Lynch syndrome, and most people do not need this test. This page applies once a pathogenic MLH1 fault has been confirmed in a blood or saliva sample.
If your tumour report says MLH1 was lost, ask whether a methylation test was done. It changes the answer.Questions we are asked
Common questions about MLH1 cancer risk
Will I definitely get cancer with an MLH1 fault?
No. Your risk is raised well above the general population, but many carriers never develop cancer. Regular colonoscopy lowers bowel cancer risk substantially, because growths are removed before they turn into cancer. Your counsellor will explain your own figures.
At what age do cancers usually appear?
Often younger than in the general population. Bowel cancer in carriers is often found in middle age, and sometimes much earlier. This is why colonoscopy starts in early adult life, and why the age of relatives at diagnosis matters to your plan.
Why are MLH1 risks higher than for other Lynch genes?
MLH1 sits at the centre of the repair system, so losing it disables repair more completely than losing some partner genes. Studies consistently show higher bowel and womb risks for MLH1 and MSH2 than for MSH6 and PMS2.
Is my stomach cancer risk worth checking?
It is raised, though much less than the bowel risk. A simple test for a common stomach infection is often advised, and treated if found. Some carriers are offered an upper endoscopy, especially if stomach cancer runs in the family.
Should I have my womb removed?
It is one option among several, usually discussed once a woman has completed her family. It greatly reduces womb and ovarian risk but has real effects, including early menopause if the ovaries are removed. Your gynaecologist will talk through the choice.
Does aspirin lower the risk?
A large trial found that aspirin reduced bowel cancer in people with Lynch syndrome. It is not right for everyone, because it can cause bleeding. Discuss it with your doctor before starting, and never take it without advice.
Do my children have the same risk?
Each child has a one in two chance of inheriting the fault. Those who inherit it share the same raised risks. Those who do not inherit it have ordinary population risk. Testing usually happens in early adult life, before colonoscopy would begin.
Where do I go from here?
To a genetic counsellor, who will set out your personal risks, and to a gastroenterologist for colonoscopy. Women also need a gynaecologist. Call the CION helpline if you are unsure where to start, and someone will direct you.
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
- GeneReviews (NCBI) — Lynch Syndrome
- National Cancer Institute — Genetics of Colorectal Cancer (PDQ) - Health Professional Version
- MedlinePlus Genetics — Lynch syndrome
- Cancer Research UK — 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.
Keep reading
Related pages
MLH1 carriers have the highest Lynch risks: what that meansHow MLH1 compares with the other Lynch genesSurveillance for MLH1 carriersThe checks that bring these risks downMLH1 promoter methylationWhy a tumour that lost MLH1 may not mean LynchLynch syndrome: the complete pictureThe whole condition, organ by organ
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Bring your report and your family history, and a counsellor will set out your personal risks and the checks that match them. You can ask everything in Telugu. One helpline serves every CION centre.