Medical Oncologist
CION Cancer Clinics
STK11 and cancer: which cancers, and how much risk | CION Cancer Clinics
An inherited STK11 fault causes Peutz-Jeghers syndrome. It raises the risk of several cancers over a lifetime, mostly in the bowel, stomach, pancreas and breast, and in the ovaries, cervix or testes. The overall risk is substantially higher than in the general population, but it is spread over decades. This page explains which cancers are involved, and at what stage of life each one 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
- Which cancers does an STK11 fault raise the risk of?
- Where in the body is the risk raised?
- How does the risk change as a person gets older?
- The words you will meet, in plain language
- What does a raised risk mean, and what does it not?
- What this page cannot tell you
- Four things families tell us, and what is actually true
- Common questions about STK11 and cancer risk
The short answer
Which cancers does an STK11 fault raise the risk of?
An inherited STK11 fault causes Peutz-Jeghers syndrome. It raises the risk of cancer in the gut, the pancreas, the breast and the reproductive organs. Added together, the lifetime risk is substantially higher than in the general population. It is spread over many decades, and it is not a certainty for any one person.
The polyps usually come first
Most families learn about the condition through polyps in the gut and dark freckles on the lips, inside the mouth or on the fingers. These polyps are a type called hamartomas. They are not cancer. In childhood their main danger is that a large one can block the bowel.
Why the list of cancers is so long
STK11 acts as a brake on cell growth in many tissues, not just one organ. When one copy is faulty from birth, that brake is weaker all over the body. So the cancers are spread across several organs rather than grouped in one place, and the checks have to cover each of them.
Risk figures for this syndrome come from small studies. They vary widely, and they describe groups of people, not you.Organ by organ
Where in the body is the risk raised?
The risks fall into four groups. Each group has its own checks, and its own age at which the checks begin.
The bowel, stomach and small bowel
Cancers of the digestive tract are among the most common in this syndrome, and the large bowel carries the biggest share. This is why regular camera tests of the gut form the core of the plan.
Usually checked with
- Colonoscopy of the large bowel
- Upper endoscopy of the stomach
- A capsule camera or MRI of the small bowel
The pancreas
The risk of pancreatic cancer is clearly raised, mostly from middle age. It is harder to find early than the others. Guidelines differ on when to start looking and which scan to use.
The breast
Women have a substantially raised breast cancer risk, in a similar range to some better-known breast cancer genes. It tends to appear at a younger age than usual, which is why breast checks start in early adulthood.
The reproductive organs
Women can develop rare tumours of the ovary and a rare type of cancer of the cervix. Boys can develop tumours of the testes. These are usually not cancer, but they can cause breast growth or early puberty.
Not sure whether this applies to you?
Ask an oncologistAcross a lifetime
How does the risk change as a person gets older?
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In childhood
Polyps start to grow in the gut. The main danger at this age is a blockage of the bowel called intussusception, not cancer. Boys may be checked for growths in the testes.
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In the teenage years
Polyps keep forming and are removed during camera tests. Girls can develop ovarian tumours that cause irregular periods or early puberty. Most of these are not cancer.
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In young adulthood
The risks of breast and cervical cancer start to rise. Cancers of the gut can appear years earlier than they do in the general population.
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In middle age
The risks of bowel, stomach, pancreatic and breast cancer are all higher than average and keep rising. Lung cancer risk is also raised, most of all in people who smoke.
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Across the whole of life
The list is long, but no carrier develops all of these. The checks are designed around the cancers that matter most at each age.
On your report
The words you will meet, in plain language
- Peutz-Jeghers syndrome
- The condition caused by an inherited STK11 fault. It combines gut polyps, dark freckles and a raised risk of several cancers.
- Hamartoma
- A type of polyp made of normal tissue that has grown in a disorganised way. It is not cancer.
- Intussusception
- When one part of the bowel slides inside the next, usually pulled by a large polyp. It blocks the bowel and needs urgent care.
- Pigmentation
- The dark freckles on the lips, inside the mouth or on the fingers. They are harmless and often fade in adult life.
- Adenoma malignum
- A rare type of cancer of the cervix linked to this syndrome. A routine smear test can miss it.
- Penetrance
- How often a fault leads to cancer across everyone who carries it. For STK11 it is high, but it is not every carrier.
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Side by side
What does a raised risk mean, and what does it not?
A raised risk means
It does not mean
Checks start earlier and happen more often
That cancer is certain
Symptoms are looked at sooner
That every symptom is cancer
Relatives can be tested for the exact fault
That every relative carries it
Screening choices can be planned ahead
That surgery is required
Being straight with you
What this page cannot tell you
It cannot give you your own risk. The published figures come from small groups of families, and they vary from study to study. Your own risk depends on your age, your sex, what checks you have had and what has happened in your family. What your specific variant means is a question for the counsellor who ordered the test.
It is not about STK11 on a tumour report
STK11 changes are often found inside lung tumours, in people with no family syndrome at all. Those changes are in the tumour only and cannot be passed on. They matter for treatment choices, which are covered under targeted therapy.
Who this does not apply to
Most people with a single gut polyp or a few freckles on the lips do not have this syndrome and do not need this test. Testing is usually considered when several polyps of this type are found, or when the freckles and polyps appear together, or a close relative is known to carry the fault.
Commonly believed
Four things families tell us, and what is actually true
"The polyps are cancer."
They are not. They are hamartomas, made of normal tissue grown in a disorganised way. Large ones are still removed, because they can bleed or block the bowel.
"The dark spots on the lips will turn into cancer."
The freckles are harmless and often fade with age. They matter because they are a clue to the syndrome, not because they are dangerous in themselves.
"Only the bowel needs watching."
The gut is the centre of the plan, but not all of it. The breast, pancreas and reproductive organs each need their own checks at their own ages.
"STK11 on my lung cancer report means my children are at risk."
Usually it does not. An STK11 change found only in a lung tumour is not inherited. A blood test answers the family question if there is any doubt.
Questions we are asked
Common questions about STK11 and cancer risk
What is my overall cancer risk with an STK11 fault?
Across a lifetime it is substantially higher than in the general population. The studies are small and the figures vary, so no single number is reliable for one person. A counsellor can explain what the evidence means using your age and your family history.
Which cancer is the most common?
Bowel cancer and, in women, breast cancer are among the most common. Stomach, small bowel and pancreatic cancers are also clearly raised. The exact order differs between studies, which is why the checks cover all of them.
At what age does the risk begin?
Polyps start in childhood, and their main danger then is a blocked bowel. Cancers usually appear from young adulthood onwards, earlier than in the general population. Checks are timed to start before each risk begins to rise.
Is the risk the same for men and women?
The gut and pancreas risks apply to both. Women also have raised breast, ovarian and cervical risks. Boys can develop tumours of the testes, usually not cancer. So the checks differ by sex after childhood.
Do dark freckles on the lips mean I have the syndrome?
Not on their own. Freckles are common. In this syndrome they usually appear in early childhood, on the lips and inside the mouth, alongside gut polyps. A doctor looks at the whole picture before suggesting a test.
Does removing polyps lower the cancer risk?
Removing large polyps prevents blockage and bleeding, which is its main purpose. It may also lower the gut cancer risk, but studies have not shown by how much. It does nothing for the risks outside the gut.
Can lifestyle change the risk?
Not smoking matters most, because it lowers the risks of lung and pancreatic cancer. A healthy weight and little alcohol help too. None of this removes the inherited risk, so the checks still need to happen.
Who should I talk to about my own risk?
A genetic counsellor for the result, and a gastroenterologist for the gut checks. Call the CION helpline if you are not sure where to start, 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
- GeneReviews (NCBI) — Peutz-Jeghers Syndrome
- MedlinePlus Genetics — Peutz-Jeghers syndrome
- National Cancer Institute — Genetics of Colorectal Cancer (PDQ) – Health Professional Version
- MedlinePlus Genetics — STK11 gene
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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