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The STK11 gene: what it does and why it matters | CION Cancer Clinics
STK11 is a gene that acts as a brake on cell growth and a sensor of the cell's energy supply. An inherited fault in one copy causes Peutz-Jeghers syndrome, which brings polyps in the bowel, dark freckles on the lips and a raised risk of several cancers. This page explains what the gene normally does, what goes wrong, and why an STK11 change found only in a tumour is a different matter. 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 STK11 gene actually do?
- Is my STK11 result inherited, or only in the tumour?
- How does a faulty STK11 lead to polyps and cancer?
- The words you will meet, in plain language
- What each kind of STK11 result changes
- Four things families tell us about STK11, and what is true
- What this page cannot tell you
- Common questions about the STK11 gene
The short answer
What does the STK11 gene actually do?
STK11 carries the instruction for a protein called LKB1. That protein works like a fuel gauge and a brake at the same time. When a cell is low on energy, it tells the cell to stop growing and save what it has. It also helps cells in a lining know which side faces up, so the layer stays flat and tidy.
What happens when one copy is faulty
Everyone has two copies of STK11, one from each parent. A person born with one faulty copy in every cell has Peutz-Jeghers syndrome. The lining of the bowel grows in untidy folds and forms a particular kind of polyp. Dark freckles appear on the lips, inside the mouth and on the fingers, usually in early childhood.
Why it matters beyond the bowel
The same brake works in the breast, pancreas, stomach, ovary, cervix, testis and lung. That is why carriers are watched in several organs over a lifetime. The plan is set by a team who know the syndrome, and it changes as a person grows from a child into an adult.
STK11 faults are rare. Most people with a bowel polyp or with freckles on the face do not carry one.Two very different reports
Is my STK11 result inherited, or only in the tumour?
The same gene name appears on two kinds of report. Knowing which one you are holding changes almost everything that follows.
Inherited, from birth
Found on a blood or saliva test. The fault sits in every cell and can be passed to children. This is what causes Peutz-Jeghers syndrome, and relatives can be tested for the exact same change.
Usually looks like
- Polyps in the small bowel from childhood
- Dark spots on the lips and inside the cheeks
- A parent or sibling with a similar picture
Found only in a tumour
Found on a test of cancer tissue, most often lung cancer. The change arose in that tumour during life. It is not in the rest of the body and cannot reach a child. It can shape treatment, which our targeted therapy pages cover.
New in this family
Some people with the syndrome are the first in their family to have it. Their parents test negative. Their own children still face the same one in two chance of inheriting it.
Features, but no fault found
A few people have the polyps and freckles, yet testing finds no STK11 fault. They are still watched as if they had the syndrome, guided by what the doctors can see.
Not sure whether this applies to you?
Ask an oncologistFrom gene to polyp
How does a faulty STK11 lead to polyps and cancer?
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The gene reads the cell's fuel level
LKB1 switches on a second protein, called AMPK, when energy runs low. That signal slows growth and tells the cell to wait for better conditions.
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One faulty copy is present from birth
A carrier has half the usual brake in every cell. Nothing is broken yet, but the gut lining starts to grow in untidy folds, most often in the small bowel.
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Polyps cause trouble of their own
Large polyps can bleed slowly and leave a low haemoglobin. They can also drag one piece of bowel inside the next. This blockage, called intussusception, is often the first sign in a child.
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The second copy can fail in one cell
If the remaining working copy is damaged in a single cell, that cell loses the brake completely. Over many years this can lead to cancer, in the bowel or in another organ.
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Which is why watching helps
Removing large polyps early prevents blockages. Regular checks of the organs at risk find problems while they are small and easier to treat.
On your report
The words you will meet, in plain language
- STK11 or LKB1
- Two names for the same gene. Reports tend to say STK11. Research papers often say LKB1.
- Peutz-Jeghers syndrome
- The inherited condition caused by a faulty STK11. Doctors often shorten it to PJS.
- Hamartomatous polyp
- A polyp made of overgrown normal tissue in a muddled pattern. It is different from the common polyps seen in older adults.
- Mucocutaneous pigmentation
- The dark blue-brown freckles on the lips, inside the mouth and on the fingers. They often fade in adult life, except inside the cheeks.
- Pathogenic variant
- A spelling change known to break the gene. This is what a positive report means.
- Autosomal dominant
- One faulty copy is enough. Each child of a carrier has a one in two chance of inheriting it, boy or girl.
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Side by side
What each kind of STK11 result changes
Inherited STK11 fault
STK11 found only in a tumour
Brothers, sisters and children can be tested
Relatives carry no extra risk from it
Bowel checks start in childhood
Nobody's screening changes
Breast, pancreas and gynaecology checks are planned
Treatment for that one cancer may shift
A genetic counsellor leads the next steps
The treating oncologist leads the next steps
Commonly believed
Four things families tell us about STK11, and what is true
"The spots on her lips faded, so the condition has gone."
The freckles often fade after the teenage years. The gene fault does not. Polyps keep forming and the cancer risk remains, so the checks carry on into adult life.
"His tummy pains are just worms or indigestion."
In a child with the syndrome, or with the dark lip spots, repeated cramping pain can mean a polyp is causing a blockage. That needs a doctor who knows the condition, not a home remedy.
"STK11 is in my lung cancer report, so my children are at risk."
A change found only in a lung tumour usually arose in that tumour. It does not travel to children. A separate blood test checks for an inherited fault, and it is rarely needed in that situation.
"Nobody else in the family has it, so it cannot be genetic."
Some people are the first in their family to carry the fault. They can still pass it on, with a one in two chance for each child.
Being straight with you
What this page cannot tell you
It cannot tell you what the report in your hand means for you. What your specific variant means is a question for the counsellor who ordered the test. The exact change, how the laboratory classified it and your own history all shape the answer.
It cannot set your checks
When checks start, which scopes you need and which scans suit you are decided by a gastroenterologist and a genetics team who know this syndrome. The condition is rare, so guidance rests on fairly small groups of families worldwide. Studies so far are small, and plans are updated as more is learned.
Who this does not apply to
Most people with a single bowel polyp, or ordinary freckles on the face, do not need STK11 testing. The same is true for someone whose lung cancer report mentions STK11 but who has no polyps, no lip spots and no family history of either. Ask your oncologist before drawing any conclusion about your family.
If you are unsure whether your story fits, call the helpline and describe it. Someone will tell you honestly whether a genetics referral makes sense.Questions we are asked
Common questions about the STK11 gene
Is STK11 the same as LKB1?
Yes. STK11 is the name of the gene, and LKB1 is the name researchers often use for it and for the protein it makes. If one report says STK11 and an article says LKB1, they are talking about the same thing. Your counsellor will use whichever name is on your report.
How rare is Peutz-Jeghers syndrome?
It is rare everywhere, and good Indian figures do not yet exist. It is seen in every community. Many families only learn of it after a child is admitted with a bowel blockage, or when an adult is found to have unusual polyps during a scope.
Can someone have the syndrome without the freckles?
Yes. The spots vary from person to person, can be faint, and often fade in adult life. Some carriers are only picked up through testing because a relative was diagnosed. Absent freckles do not rule the condition out.
Does an STK11 fault mean I will get cancer?
No. It raises the risk of several cancers well above that of the general population, but many carriers never develop one. Regular checks and early removal of large polyps are how that risk is kept in hand.
Why does my lung cancer report mention STK11?
Lung tumours are often tested for many gene changes to guide treatment. STK11 is one of them. A change found this way almost always arose inside the tumour. Ask your oncologist what it means for your treatment, and whether an inherited test is needed at all.
What kind of sample does the inherited test need?
A blood sample is normally enough, and saliva is sometimes used. STK11 is often tested as part of a panel of polyp genes. Once a fault is known in a family, relatives can be tested for that single change, which is simpler and cheaper.
Should my children be tested?
Usually yes, and earlier than for most cancer genes. Polyp problems can start in childhood, so knowing early decides whether a child needs scopes. Your counsellor will talk through timing with you and, where they are old enough, with the child.
Where do I start in Hyderabad?
Gather any scope reports, polyp results and a list of who in the family had polyps or cancer, with rough ages. Take these to a genetic counsellor or your gastroenterologist. Call the CION helpline if you are unsure who to see, and someone will guide you, in Telugu if you prefer.
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 — STK11 gene
- MedlinePlus Genetics — Peutz-Jeghers syndrome
- GeneReviews (NCBI) — Peutz-Jeghers Syndrome
- National Cancer Institute — Genetics of Colorectal Cancer (PDQ) – Health Professional Version
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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Has STK11 turned up on a report in your family?
Tell us what the report says and who in the family has had polyps or cancer. We will tell you honestly whether a genetics referral is worth making, and arrange it if it is. One helpline serves every CION centre.