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SMARCB1 and SMARCA4 mutation: which cancers and what risk | CION Cancer Clinics
An inherited fault in SMARCB1 or SMARCA4 raises the chance of rhabdoid tumours, rare cancers that mostly affect babies and very young children. SMARCA4 faults also raise the chance of a rare ovarian cancer in young women. The two genes carry very different levels of risk. This page explains which tumours are linked to each gene, when the risk is highest, and what the numbers cannot tell you. 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 are linked to SMARCB1 and SMARCA4 faults?
- What are the tumours doctors watch for?
- How does the risk change as a child grows up?
- What do the words on a rhabdoid report mean?
- How do SMARCB1 and SMARCA4 risks compare?
- What can this page not tell you?
- What do parents often believe about these genes?
- Common questions about SMARCB1 and SMARCA4 risks
The short answer
Which cancers are linked to SMARCB1 and SMARCA4 faults?
An inherited fault in SMARCB1 or SMARCA4 raises the chance of rhabdoid tumours. These are rare, fast-growing cancers of the brain, kidney and soft tissues that mostly affect babies and very young children. A SMARCA4 fault also raises the chance of a rare ovarian cancer in girls and young women. Together these make up rhabdoid tumour predisposition syndrome.
The risk is concentrated early in life
For SMARCB1, most tumours appear in the first few years of life, often before a child turns three. After early childhood the chance of a new rhabdoid tumour falls sharply. That timing drives everything about care, because the most intensive checks happen in infancy.
The two genes do not carry the same risk
Most children with the common kind of SMARCB1 fault do develop a tumour, although a few carriers stay well into adult life. SMARCA4 is different. Many carriers, men and women, never develop any tumour, and the ovarian cancer affects only a minority of female carriers. Studies of both genes are small, so every figure is an estimate.
A fault in either gene is rare. Most childhood cancers and most ovarian cancers have nothing to do with these genes.The linked cancers
What are the tumours doctors watch for?
The first three are all rhabdoid tumours. They look alike under the microscope and differ mainly in where they grow.
In the brain
Atypical teratoid rhabdoid tumour, often shortened to AT/RT. It usually grows in the back of the brain and is the most common rhabdoid tumour in carriers.
Signs parents notice
- Repeated vomiting, often in the morning
- A baby's head growing unusually fast
- Unsteadiness, or losing skills already learned
In the kidney
Malignant rhabdoid tumour of the kidney. It usually shows up as a swollen tummy or a lump, sometimes with blood in the urine. It is different from the more common Wilms tumour, though both affect young children.
Elsewhere in the body
Rhabdoid tumours can also grow in the neck, spine, liver or soft tissues. A carrier can have more than one tumour at the same time, which is itself a strong clue that the fault is inherited.
In the ovary: SMARCA4
Small cell carcinoma of the ovary, hypercalcaemic type. It is a rare, aggressive cancer that usually affects young women, and it often raises the calcium level in the blood.
This cancer is covered in detail on its own page, linked below.Not sure whether this applies to you?
Ask an oncologistAcross a lifetime
How does the risk change as a child grows up?
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Before birth and in the first months
Rhabdoid tumours can be present at birth or appear within the first months. This is the period of highest risk for SMARCB1 carriers.
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The toddler years
The risk stays high through the first few years. Brain and kidney tumours are both still possible, which is why checks cover the head and the abdomen.
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After early childhood
The chance of a new rhabdoid tumour drops a great deal. Many teams ease the pace of brain scans at this point, though some checks of the abdomen may continue.
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Adolescence and young adulthood
For girls and women with a SMARCA4 fault, this is when the ovarian cancer usually appears. Their checks shift towards the pelvis.
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Adult life
A few SMARCB1 carriers develop slow-growing nerve or brain lining tumours called schwannomas and meningiomas. These are not rhabdoid tumours and are far less dangerous.
On your report
What do the words on a rhabdoid report mean?
- Rhabdoid tumour
- A cancer named for how its cells look under a microscope. It is defined by the loss of SMARCB1 or SMARCA4 inside the tumour.
- INI1 loss
- INI1 is another name for the SMARCB1 protein. A tumour report saying INI1 is lost describes the tumour, not whether the fault is inherited.
- Germline
- Present in every cell from birth and therefore inheritable. Checked with a blood test, separate from the tumour test.
- Penetrance
- How often a fault actually leads to a tumour among everyone who carries it. It is high for SMARCB1 and much lower for SMARCA4.
- Synchronous tumours
- Two or more separate tumours found at the same time. This pattern makes an inherited fault more likely.
- Truncating variant
- A fault that cuts the gene's instruction short. This kind is the one most strongly linked to rhabdoid tumours.
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Side by side
How do SMARCB1 and SMARCA4 risks compare?
SMARCB1
SMARCA4
The more common cause of the syndrome
A much rarer cause
Brain, kidney and soft tissue tumours
Mainly ovarian cancer, rarely brain tumours
Most carriers develop a tumour
Many carriers never develop a tumour
Often new in the child, not from a parent
Often inherited from a healthy parent
Risk centred on infancy
Ovarian risk centred on young adult women
Being straight with you
What can this page not tell you?
It cannot tell you the risk for your child. Risk depends on the gene, the exact kind of fault and sometimes the family's own history. What your specific variant means is a question for the counsellor who ordered the test.
The numbers are uncertain
This syndrome is rare everywhere, and almost all the published data come from small groups of families in Europe and North America. Studies so far are small. We have deliberately not quoted percentages here, because a figure from a handful of families can mislead more than it helps.
Who this does not apply to
If SMARCA4 appeared on the report of an adult lung tumour, that change is almost always inside the cancer and linked to smoking, not inherited. That kind of finding is covered in our targeted therapy pages. Most families with a child who has cancer do not carry either of these genes.
If you are holding a tumour report that mentions INI1 or SMARCB1, ask whether a blood test for an inherited fault has been arranged.Commonly believed
What do parents often believe about these genes?
"Neither of us has the fault, so our other children are safe."
Not always. A parent can carry the fault only in some egg or sperm cells, which a blood test cannot see. Siblings are sometimes affected even when both parents test negative.
"We must have done something during the pregnancy."
Nothing a parent did or did not do causes these gene faults. Most SMARCB1 faults arise by chance when the egg or sperm forms. Guilt is common and understandable, but it is misplaced.
"A SMARCA4 carrier will certainly get ovarian cancer."
Many women carrying a SMARCA4 fault never develop it. Healthy older carriers are well documented. The risk is real enough to plan for, but it is far from certain.
"Once a child passes five, the danger is over."
The risk of new rhabdoid tumours falls sharply after early childhood, but it does not reach zero. Girls with SMARCA4 faults also face a later ovarian risk that needs its own plan.
Questions we are asked
Common questions about SMARCB1 and SMARCA4 risks
How likely is a carrier to develop a tumour?
For the common kind of SMARCB1 fault, most carriers develop a rhabdoid tumour in early childhood. For SMARCA4, many carriers never develop any tumour. Your counsellor can say which group your family's variant falls into, and how confident that estimate is.
Can an adult carry the fault without ever being ill?
Yes. This is common with SMARCA4 and happens occasionally with SMARCB1. Healthy adult carriers are often found only after a child or niece is diagnosed, when the family is tested.
Are boys and girls at equal risk?
For rhabdoid tumours of the brain, kidney and soft tissues, yes. The ovarian cancer linked to SMARCA4 affects only girls and women, which is why their surveillance continues after early childhood and a boy's usually does not.
Is schwannomatosis the same condition?
No. Certain other changes in SMARCB1 cause schwannomatosis, a condition of mostly non-cancerous nerve tumours in adults. The kind of change matters. Your counsellor will say which condition your family's variant is linked to.
Does an inherited fault change how the tumour is treated?
The tumour is treated on its own merits by a paediatric oncology team. Knowing the fault is inherited mainly changes what happens next. It means close watching for a second tumour and testing for brothers, sisters and parents.
Can a second tumour appear after treatment?
Yes. A carrier can develop a new rhabdoid tumour in a different place, which is why a child treated for a brain tumour may still have scans of the abdomen. Your team will explain which checks continue after treatment ends.
Do these genes raise the risk of common adult cancers?
There is no clear evidence that they raise the risk of common adult cancers such as breast or bowel cancer. Adult carriers are usually advised to follow ordinary screening, plus any specific plan their team recommends.
Who can explain our family's risk properly?
A genetic counsellor or clinical geneticist working with a paediatric oncology team. Take the tumour report and any blood test result with you. The CION helpline can help you find the right clinic, and you can ask for the conversation in Telugu.
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
- National Cancer Institute — Rhabdoid Tumor Predisposition Syndrome Type 1 (PDQ) - Health Professional Version
- National Cancer Institute — Rhabdoid Tumor Predisposition Syndrome Type 2 (PDQ) - Health Professional Version
- GeneReviews (NCBI) — Rhabdoid Tumor Predisposition Syndrome
- MedlinePlus Genetics — Rhabdoid tumor predisposition syndrome
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
Rhabdoid tumour predisposition syndromeThe whole syndrome, explained from the startSMARCA4 and small cell carcinoma of the ovaryThe ovarian cancer linked to SMARCA4, in detailTesting the family for SMARCA4 and SMARCB1Who else should be tested, and why parents testing negative is not the endSMARCA4 and SMARCB1 positive: what happens nextThe first steps after a positive result
Talk to us
Has your child's tumour report mentioned SMARCB1 or INI1?
Tell us what the report says and who in the family has been tested. We will help you reach a genetics team who can explain your family's risk properly. One helpline serves every CION centre.