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MLH1 promoter methylation and why it changes the answer | CION Cancer Clinics
MLH1 promoter methylation means the tumour switched off its own MLH1 gene with a chemical tag, rather than through an inherited fault. In most cases it points away from Lynch syndrome. This page explains why a tumour loses MLH1, how the methylation test fits into the testing pathway, and what each result means for you and your relatives. 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 MLH1 promoter methylation mean on a tumour report?
- The possible reasons a tumour has lost MLH1
- How your team works out which explanation fits
- The words you will meet, in plain language
- Methylated or not: what each result changes
- Four things patients tell us, and what is actually true
- What this page cannot tell you
- Common questions about MLH1 methylation
The short answer
What does MLH1 promoter methylation mean on a tumour report?
It means the MLH1 gene was switched off inside the tumour by a chemical tag, not by an inherited fault. In most cases this points away from Lynch syndrome. The cancer happened in that one organ, and relatives are usually not at the raised inherited risk that Lynch would bring.
Why the question comes up at all
Many bowel and womb cancers are now checked for a missing repair protein. When MLH1 is missing, there are two main explanations. Either the person inherited a faulty MLH1 gene, which is Lynch syndrome, or the tumour silenced a normal gene on its own. The methylation test tells these two apart.
What the promoter is
The promoter is the stretch of DNA just in front of a gene that acts as its on switch. When chemical tags called methyl groups pile up there, the switch is jammed off. The gene itself is not broken, but it is no longer read.
Methylation found only in the tumour is acquired during life. It is not in the egg or sperm, so it is not passed down.Why MLH1 goes missing
The possible reasons a tumour has lost MLH1
A missing MLH1 protein is a clue, not a diagnosis. These are the explanations your team works through.
Methylation in the tumour
The most common reason, especially in older patients. The tumour has silenced its own MLH1 gene. This is not inherited and does not point to Lynch syndrome.
An inherited MLH1 fault
The person was born with one faulty copy, and the tumour lost the other. This is Lynch syndrome, and relatives can be tested for the same fault.
Methylation present from birth
Rarely, the MLH1 switch is jammed off in every cell of the body, not just the tumour. This is called a constitutional epimutation. It behaves much like Lynch syndrome.
It is found by testing blood, not tumour.Two faults in the tumour alone
Sometimes neither methylation nor an inherited fault is found. Both copies of a repair gene may have been damaged inside the tumour only.
- Often called Lynch-like syndrome
- Needs further tumour testing
Not sure whether this applies to you?
Ask an oncologistThe testing pathway
How your team works out which explanation fits
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The tumour is stained for repair proteins
A pathologist checks tumour tissue for four repair proteins. MLH1 missing, usually with its partner PMS2, starts the next step.
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For bowel tumours, a BRAF test may come first
A particular change in a gene called BRAF strongly suggests the tumour arose on its own. If it is present, Lynch syndrome becomes unlikely.
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The MLH1 promoter is checked for methylation
This is done on the tumour tissue already removed. No new sample is needed. For womb tumours this step is especially useful, because the BRAF test does not help there.
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If there is no methylation, a blood test follows
A germline test on blood or saliva looks for an inherited MLH1 fault. This is the test that confirms or rules out Lynch syndrome.
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A young patient may be tested even if methylated
When the patient is unusually young, or the family history is strong, the team may check blood for methylation present from birth.
On your pathology report
The words you will meet, in plain language
- Immunohistochemistry
- A stain on tumour tissue that shows whether each repair protein is present or missing. Often shortened to IHC.
- MMR-deficient
- The tumour has lost one or more of its mismatch repair proteins. It says nothing yet about the cause.
- Promoter
- The on switch just in front of a gene, which controls whether the gene is read.
- Hypermethylation
- Too many chemical tags on that switch, jamming it off. Reports may say methylation detected or methylated.
- BRAF V600E
- A change in the BRAF gene found in some bowel tumours. It points towards a cancer that arose on its own.
- Germline test
- A blood or saliva test for faults present from birth. It is the only test that diagnoses Lynch syndrome.
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Side by side
Methylated or not: what each result changes
Methylation found in the tumour
No methylation found
Lynch syndrome is unlikely
Lynch syndrome must be ruled in or out
A germline test is usually not needed
A germline test is recommended
Relatives follow family-history screening
Relatives wait for the germline result
Your own follow-up is standard for the cancer
Your follow-up may change if Lynch is confirmed
Commonly believed
Four things patients tell us, and what is actually true
"My tumour lost MLH1, so I have Lynch syndrome."
Not necessarily. In many people, especially older patients, the tumour silenced MLH1 itself. Only a germline blood test can diagnose Lynch syndrome.
"Methylation means my family is completely safe."
It means an inherited MLH1 fault is unlikely. Relatives may still need screening if the family history is strong for other reasons. Your team looks at both.
"Methylation is caused by what I ate."
Methylation of MLH1 in tumours becomes more common with age. No single food or habit has been shown to cause it, and it is not something you did wrong.
"If my tumour is methylated, repair loss no longer matters."
The tumour is still MMR-deficient, whatever the cause. That can affect which medicines work, including immunotherapy. Your oncologist will take it into account.
Being straight with you
What this page cannot tell you
It cannot tell you which explanation fits your tumour. That depends on the pathology report, your age, the type of cancer and your family history, read together. Not every laboratory in India offers the methylation test, so some samples are sent away, which can add time.
It cannot read your report
What your specific result means is a question for the counsellor or oncologist who ordered the test. A partly methylated result, or a result from a small sample, can be hard to read and may need repeating.
Who this does not apply to
If your tumour has all four repair proteins present, this question does not arise. If you already have a confirmed inherited MLH1 fault, the methylation result no longer changes your diagnosis. Most people reading about Lynch syndrome do not need this test at all.
Questions about using the tumour result to choose medicines belong with your oncologist and the targeted therapy team.Questions we are asked
Common questions about MLH1 methylation
Do I need a new biopsy for the methylation test?
Usually not. The test is run on tissue already removed at surgery or biopsy, which the laboratory keeps in a small wax block. Ask the hospital that did your surgery to release the block to the testing laboratory.
My tumour is methylated. Should my children be tested?
Usually not for Lynch syndrome. Methylation found only in the tumour is not inherited. Your children may still need earlier bowel screening if several relatives had bowel cancer, so share the family history with your counsellor.
Why is the BRAF test used for bowel but not womb cancer?
In bowel cancer, the BRAF change is a reliable sign that the tumour arose on its own. In womb cancer, that change is rare, so it does not help. Methylation testing is used directly instead.
What is a constitutional epimutation?
It is when the MLH1 switch is jammed off in every cell from birth, not only in the tumour. It is rare. It raises cancer risk much like Lynch syndrome, and in some families it can be passed on. It is found with a blood test.
What if there is no methylation and no inherited fault?
This is sometimes called Lynch-like syndrome. Both copies of a repair gene may have been damaged inside the tumour alone. Further tumour testing can often show this. Until it is clear, relatives may be screened as though Lynch were possible.
Does methylation change my treatment?
The tumour is still MMR-deficient, which can affect whether some medicines, including immunotherapy, are likely to help. That is a treatment question for your oncologist, not a family question.
Is this test covered under Aarogyasri or Ayushman Bharat?
Coverage for specialised tumour tests varies and changes over time. Ask the hospital billing desk before the sample is sent. Your counsellor can also tell you whether the test is likely to change anything for you.
Who should explain my result?
The oncologist or genetic counsellor who ordered it. Bring the full pathology report, including the repair protein stains. 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)
Medical Oncologist
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Sources
- GeneReviews (NCBI) — Lynch Syndrome
- National Cancer Institute — Genetics of Colorectal Cancer (PDQ) - Health Professional Version
- NICE — Molecular testing strategies for Lynch syndrome in people with colorectal cancer (DG27)
- MedlinePlus Genetics — What is the epigenome?
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
Lynch-like syndrome: MMR loss without a germline causeWhen neither methylation nor an inherited fault is foundMMR IHC on the tumour as a route into Lynch testingThe stain that starts this whole questionMLH1 mutation: which cancers and what riskWhat an inherited MLH1 fault would meanColorectal cancer under 50 and universal MMR testingWhy every bowel tumour is now checked
Talk to us
Not sure what your tumour report is saying about MLH1?
Bring the full pathology report and a counsellor will explain whether a germline test is needed. We can explain every step in Telugu. One helpline serves every CION centre.