Medical Oncologist
CION Cancer Clinics
NBN mutation: which cancers, and how much risk | CION Cancer Clinics
For adults with one faulty copy of NBN, the cancer studied most is breast cancer, and the rise in risk looks modest. The clearest evidence comes from a single fault common in Eastern Europe. Children with two faulty copies face a very different picture, including a high risk of lymphoma. This page sets out what is known, what is not, and how your own risk is worked out. 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 NBN fault raise the risk of?
- What is known about each cancer linked to NBN?
- How does a counsellor work out your own risk?
- What do the risk words in your report mean?
- How do the risks differ with one fault and with two?
- What can this page not tell you?
- What do people believe about NBN risk that is not true?
- Common questions about NBN and cancer risk
The short answer
Which cancers does an NBN fault raise the risk of?
For an adult with one faulty copy of NBN, the cancer studied most is breast cancer, and prostate cancer has also been suggested. The rise in risk looks modest, and the strongest evidence comes from a single fault common in Eastern Europe. For children with two faulty copies, the picture is very different, with a high risk of lymphoma, a cancer of the immune system.
Why the answer depends on which fault you have
Most research on NBN carriers has looked at one founder fault, handed down in Polish, Czech and neighbouring families. Studies of that fault found a moderately raised breast cancer risk. Studies of other NBN faults are small, and many have not found a clear effect. So two carriers with different faults may not face the same risk.
Why guidelines have become more cautious
As larger studies have come in, the case for treating every NBN fault as a breast cancer gene has weakened. Several guidelines now advise that most NBN carriers should be screened according to their family history rather than the result alone. That is a sign the science is still settling. It does not mean your result was a mistake.
One faulty copy and two faulty copies carry very different risks. Check which one your report describes.Cancer by cancer
What is known about each cancer linked to NBN?
The strength of the evidence varies a great deal. Here is where each one stands today.
Breast cancer
The best-studied link. The Eastern European founder fault is linked to a moderately raised risk, below what is seen with BRCA1 or BRCA2. For other NBN faults, the evidence is weaker and less consistent.
What it usually means
- Screening planned around your family history
- Preventive surgery is not usually advised on this result
Prostate cancer
Some studies of the founder fault found more prostate cancer in male carriers. Numbers are small, and the link is less certain than for breast. Men in the family should still know the result.
Other cancers reported
Links with melanoma, lymphoma, bowel and ovarian cancer have been reported in single studies. None is firm enough to change screening for carriers.
Childhood cancers with two faults
Children with Nijmegen breakage syndrome have a very high risk of lymphoma before adult life. Brain tumours and some rare childhood cancers have also been seen.
Not sure whether this applies to you?
Ask an oncologistHow risk is weighed
How does a counsellor work out your own risk?
Which exact fault you carry
The counsellor checks whether your fault is the well-studied founder fault or a different one. This single detail shapes how much weight the result can carry.
Who in the family had cancer
A family tree covering both sides, with ages at diagnosis, often says more about your risk than the NBN result does. Men and relatives who have died are included.
Your own age, sex and history
Risk is not the same for a young woman, an older woman and a man. Any earlier breast biopsies and your breast density also count.
Whether other genes were checked
A panel that found NBN also looked at BRCA1, BRCA2 and others. A clear result on those genes is as important as the NBN finding.
Risk words
What do the risk words in your report mean?
- Lifetime risk
- The chance of developing a cancer at some point across your whole life. It is the figure most useful for planning.
- Relative risk
- How your risk compares with someone without the fault. A doubling sounds large, but it may still be a modest chance overall.
- Penetrance
- How often a fault actually leads to cancer across everyone who carries it. For NBN, it is low to moderate and not well measured.
- Moderate-risk gene
- A gene whose faults raise risk less than BRCA1 or BRCA2 do. NBN is usually placed in this group or below it.
- Founder variant
- A fault shared by many families who descend from a common ancestor. Much NBN research rests on one such fault.
- Biallelic
- Both copies of the gene are faulty. In NBN, this causes Nijmegen breakage syndrome in childhood.
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Side by side
How do the risks differ with one fault and with two?
One faulty copy
Two faulty copies
Usually found in adult life on a gene panel
Usually recognised in early childhood
Modestly raised breast cancer risk, for some faults
Very high risk of lymphoma in childhood
Screening mainly guided by family history
Close watch by a specialist children's team
Routine scans and treatment usually as normal
Radiation and some chemotherapy need great care
Being straight with you
What can this page not tell you?
It cannot put a number on your own risk. What your specific variant means is a question for the counsellor who ordered the test. We have left out risk figures on purpose, because for most NBN faults the published figures are uncertain and vary from one study to the next.
It cannot tell you how NBN behaves in Indian families
Almost all NBN research comes from European families. Indian data are very limited, and the faults found in Indian patients are often different from the Eastern European founder fault. Studies so far simply have not looked closely at people like you.
Who this does not apply to
If your NBN result came from a tumour test, it describes the tumour and may not be inherited. That is covered under targeted therapy. And if your report calls the change a variant of uncertain significance, none of the risks on this page apply to you until it is reclassified.
A strong family history can matter more than the NBN result itself. Bring the family tree to every appointment.Commonly believed
What do people believe about NBN risk that is not true?
"Any breast cancer gene means I need surgery."
Preventive surgery is discussed for high-risk genes such as BRCA1 and BRCA2. For NBN, it is not usually advised on the result alone. Screening is the usual response, if anything changes at all.
"The risk figure I read online applies to me."
Most published figures come from one European founder fault. Your fault may be different, and your family history changes the picture further. Online figures can badly overstate or understate your risk.
"Men do not need to know about NBN."
Men can carry the fault and pass it on. Some studies suggest a raised prostate cancer risk. A brother or son is as entitled to testing as a sister or daughter.
"Carriers get lymphoma like the children do."
The very high lymphoma risk belongs to children with two faulty copies. There is no clear evidence of a similar risk in adults with one faulty copy.
Questions we are asked
Common questions about NBN and cancer risk
Is NBN a high-risk breast cancer gene?
No. Even the best-studied NBN fault raises breast cancer risk far less than BRCA1 or BRCA2. For many other NBN faults, a clear link has not been shown. Most carriers are screened based on their family history, which your counsellor will review with you.
Should I start breast screening early?
That depends on your family history and the exact fault, not on the gene name alone. Some carriers are offered earlier or more frequent screening because of relatives with breast cancer. Others simply follow the usual programme. Your counsellor or breast specialist will advise.
Does NBN raise ovarian cancer risk?
There is no firm evidence that it does. A few studies have reported a possible link, but it has not held up consistently. Decisions about the ovaries are not normally made on an NBN result. A family history of ovarian cancer would be weighed separately.
What about prostate cancer in men?
Some studies of the Eastern European founder fault found more prostate cancer in carriers. The evidence is limited, and other NBN faults are less studied. Male carriers can raise it with their doctor, especially if relatives had prostate cancer at a young age.
I already have breast cancer. Does NBN change my treatment?
Usually not. Treatment is planned on the tumour itself. Tell your oncologist about the result before radiotherapy, so the team has the full picture. For adults with one faulty copy, there is no clear evidence that standard treatment is unsafe.
Why did my report find NBN if it matters so little?
Wide panels test many genes at once, including some whose effect is still being studied. That means results like NBN turn up often. It is real information, but its weight is smaller than the report's wording may suggest.
Could my NBN result be reclassified?
Yes. Laboratories review their calls as evidence grows, and guidelines on NBN have already changed. Ask the laboratory or your counsellor how you will be told if anything changes. Keep a copy of your report so it can be looked at again.
Who should I talk to about my risk?
A genetic counsellor or clinical geneticist is the right person. Bring the report and a family tree with ages at diagnosis. Counselling in Telugu can be arranged. Call the CION helpline if you are unsure where to begin, 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)
Medical Oncologist
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Sources
- National Cancer Institute — Genetics of Breast and Gynecologic Cancers (PDQ) – Health Professional Version
- GeneReviews (NCBI) — Nijmegen Breakage Syndrome
- MedlinePlus Genetics — NBN gene
- National Cancer Institute — Genetic Testing for Inherited Cancer Susceptibility Syndromes
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
The NBN gene: what it doesHow the gene works, before the risks make senseNBN positive: what happens nextThe practical steps once you have a resultBiallelic NBN and Nijmegen breakage syndromeThe childhood condition behind the lymphoma riskLow-penetrance variants and why they confuse peopleWhy a real result can still change very little
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Bring your report and a family tree with ages at diagnosis. A counsellor will tell you honestly how much the result changes. One helpline serves every CION centre.