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The FLCN gene: what it does and why it matters | CION Cancer Clinics
The FLCN gene works like a brake on cell growth in the skin, lungs and kidneys. An inherited fault in it causes Birt-Hogg-Dubé syndrome, which brings harmless skin bumps, lung cysts and a raised chance of kidney tumours. This page explains what the gene does, how the fault is passed on, and why carriers are offered regular kidney scans rather than treatment. 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 FLCN gene actually do?
- Which parts of the body does an FLCN fault affect?
- Why does a faulty FLCN gene lead to kidney tumours?
- What do the words on an FLCN report mean?
- How is BHD different from ordinary kidney cancer?
- What can this page not tell you?
- What do families get wrong about FLCN?
- Common questions about the FLCN gene
The short answer
What does the FLCN gene actually do?
FLCN is a gene that helps cells decide when to grow and when to rest. It makes a protein called folliculin, which works like a brake in the skin, the lungs and the kidneys. When one copy of FLCN is faulty from birth, that brake is weaker in every cell.
The condition it causes
An inherited FLCN fault causes Birt-Hogg-Dubé syndrome, usually shortened to BHD. It has three main signs. Small harmless bumps appear on the face and neck. Thin-walled air pockets called cysts form in the lungs. And the kidneys have a raised chance of developing tumours, some of which are cancers.
Why it matters to your family
BHD is passed down in a simple pattern. Each child of a carrier has a one in two chance of inheriting the fault. Knowing about it means relatives can be tested, and carriers can have their kidneys checked before any tumour causes symptoms. Most kidney tumours in BHD grow slowly, and finding them small keeps the choices simple.
An FLCN fault is a statement about risk. It is not a cancer diagnosis.Where it shows up
Which parts of the body does an FLCN fault affect?
The same fault can look very different from one relative to the next. Some carriers have all three signs. Some have one.
Skin
Small, pale, dome-shaped bumps, usually on the face, nose, ears and neck. They tend to appear in adult life and are harmless. Dermatologists often spot BHD first.
Lungs
Cysts in the lower parts of both lungs are found in most adult carriers on a scan. They rarely affect breathing, but one can burst and cause a collapsed lung.
A collapsed lung in a young, slim non-smoker is a reason to ask about BHD.Kidneys
Carriers have a raised chance of kidney tumours, often in both kidneys and often more than one. This is the part that needs regular checks.
Usually looks like
- Slow-growing tumours
- Found on a routine scan
- Diagnosed in middle age
Everything else
Studies have looked at other organs, including the bowel and the thyroid. The evidence so far is small and does not change routine care.
Not sure whether this applies to you?
Ask an oncologistFrom gene to tumour
Why does a faulty FLCN gene lead to kidney tumours?
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You have two copies of FLCN
One came from each parent. One working copy is enough to keep the brake on in each cell.
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A carrier starts with one working copy
The inherited fault switches off one copy in every cell from birth. Nothing goes wrong yet, because the other copy still works.
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The second copy can be lost in one cell
Over a lifetime, the working copy can be damaged by chance in a single kidney cell. That cell now has no brake at all.
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That cell can grow into a tumour
The cell divides when it should not. In BHD this usually happens slowly, which is why regular scans can find tumours while they are still small.
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Which is why carriers are watched, not treated
Nothing needs to be done to a healthy kidney. The aim is to find the second step early if it ever happens.
On your report
What do the words on an FLCN report mean?
- FLCN
- The gene's short name. It stands for folliculin, the protein the gene makes.
- Birt-Hogg-Dubé syndrome
- The condition caused by an inherited FLCN fault. It is named after the three doctors who first described it.
- Pathogenic variant
- A change in the gene known to stop it working. This is what people mean by a gene fault.
- Germline
- Present in every cell from birth, so it can be passed on. It is different from a fault found only inside a tumour.
- Fibrofolliculoma
- The medical name for the small skin bumps. They are harmless.
- Pneumothorax
- A collapsed lung, when air leaks out of the lung into the chest.
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Side by side
How is BHD different from ordinary kidney cancer?
Kidney tumours in BHD
Kidney cancer in most people
Often in both kidneys
Usually one tumour in one kidney
Often found earlier in adult life
Usually found later in life
Surgeons try hard to save kidney tissue
Removing the whole kidney is sometimes fine
Relatives can be tested
No family test is needed
Being straight with you
What can this page not tell you?
It cannot tell you what your own result means. What your specific variant means is a question for the counsellor who ordered the test. The same gene can carry very different changes, and only someone who has seen the full report and your family tree can read it.
It cannot give you your personal risk
Published risk figures for BHD come from small groups of families, mostly outside India. They vary from study to study. Your doctor will talk about risk in terms of what checks you need, not a single number.
Who this does not apply to
Most people with kidney cancer do not have BHD, and most people with a collapsed lung do not either. If nobody in your family has the skin bumps, lung cysts or kidney tumours at a young age, an FLCN test is unlikely to be useful. Kidney tumour testing on the tumour itself is a different question, covered on our targeted therapy pages.
Commonly believed
What do families get wrong about FLCN?
"The skin bumps are a sign of cancer."
They are harmless. They matter only because they point to the gene fault, which is why the kidneys then need checking.
"A collapsed lung is just bad luck."
Usually it is. But a collapsed lung that runs in the family, or one in a young person with lung cysts on the scan, is worth raising with a doctor. It is sometimes the first clue to BHD.
"Every carrier will get kidney cancer."
Many carriers never develop a kidney tumour. The risk is raised, not certain, and regular scans are there to catch the ones that do early.
"Only the person with symptoms needs a test."
A carrier can have no skin bumps and no lung trouble at all and still pass the fault on. Once a fault is found, adult relatives can be offered a test for that exact change.
Questions we are asked
Common questions about the FLCN gene
Is BHD a type of cancer?
No. BHD is an inherited condition that raises the chance of kidney tumours, some of which are cancers. Many carriers live their whole lives with only the skin bumps or lung cysts. The syndrome itself is a reason for checks, not for treatment.
How is an FLCN fault passed on?
It is passed in a dominant pattern. A carrier has a one in two chance of passing it to each child, whether the child is a son or a daughter. It can come from either parent, and it does not skip generations, even if the illness seems to.
Can a person have BHD without knowing it?
Yes, often. The skin bumps are easy to mistake for ordinary spots, and lung cysts cause no symptoms until one bursts. Many families only find out when one relative has a collapsed lung or a kidney tumour and a doctor asks the right questions.
What test finds an FLCN fault?
A blood or saliva sample is sent for germline genetic testing. FLCN may be tested on its own or as part of a panel of kidney cancer genes. Your counsellor will decide which fits your family history best.
Do the skin bumps need removing?
Only if they bother you. They are harmless. A dermatologist can treat them for appearance, but they often come back. Removing them has no effect on the kidney or lung risk.
Should I stop smoking if I carry an FLCN fault?
Yes. Smoking damages the lungs further and raises the risk of kidney cancer in everyone. For a carrier, both of those matter more. It is one of the few things fully in your hands.
Is FLCN testing covered by insurance or Aarogyasri?
Coverage for germline genetic tests varies between policies and schemes, and it changes. Ask the CION helpline or your insurer before the sample is taken, so you know the cost upfront. India also has no specific law on genetic discrimination in insurance.
Where do I start if BHD is suspected in my family?
Write down who had skin bumps, a collapsed lung or a kidney tumour, and at roughly what age, on both sides. Take that to a genetic counsellor or your doctor. Call the CION helpline if you are not sure who to see, and we 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) — Birt-Hogg-Dubé Syndrome
- MedlinePlus Genetics — FLCN gene
- MedlinePlus Genetics — Birt-Hogg-Dubé syndrome
- National Cancer Institute — Genetics of Kidney Cancer (Renal Cell Cancer) (PDQ)
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
FLCN mutation: which cancers and what riskWhat the kidney risk actually looks likeLung cysts, collapsed lung and FLCNThe lung side of BHD, and what to do if a lung collapsesSurveillance for FLCN carriersWhich scans carriers have, and how oftenTesting the family for FLCNWho should be tested once a fault is found
Talk to us
Has someone in your family been told they have BHD?
Tell us who was affected and how. We will help you find a genetic counsellor and work out who else in the family should be tested. One helpline serves every CION centre.