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Is this retinoblastoma inherited? How testing answers it | CION Cancer Clinics
A genetic test for a gene called RB1 can usually tell you whether your child's retinoblastoma is the inherited kind. Tumours in both eyes almost always are. One eye often is not, but a smaller group still carry the fault. This page explains how testing works, why the removed tumour helps, and what each answer means for brothers, sisters and your child's future. At CION Cancer Clinics, our oncologists plan screening and care for families with an inherited cancer syndrome, explained in plain words.
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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
- Can a test tell us whether our child's retinoblastoma was inherited?
- What does the pattern in the eyes already suggest?
- What happens between the diagnosis and the answer?
- The words you will meet, in plain language
- What each result changes for your family
- Four things parents tell us, and what is actually true
- What this page cannot tell you
- Common questions about whether retinoblastoma is inherited
The short answer
Can a test tell us whether our child's retinoblastoma was inherited?
Usually, yes. A genetic test looks for a fault in a gene called RB1, first in the tumour where possible and then in a blood sample. If the same fault is in the blood, it is in every cell, and the retinoblastoma is the inherited kind.
Two kinds of retinoblastoma
In the non-inherited kind, both copies of RB1 were damaged inside one cell of one eye, by chance, after the baby was conceived. Nothing is in the rest of the body and nothing can be passed on. In the inherited kind, one faulty copy was present from the very start, in every cell. Only one more chance event is then needed in any cell of the retina, which is why these children often have tumours in both eyes.
Why the answer matters so much
It decides three things. How closely the other eye is checked. Whether brothers and sisters need eye examinations from birth. And whether the child carries a raised risk of other cancers later in life, which shapes follow-up for decades.
Most children with the inherited kind are the first in their family. No family history does not mean not inherited.Before any test
What does the pattern in the eyes already suggest?
Doctors can make a good first guess from how the disease looks. Only the test confirms it, and guesses can be wrong.
Tumours in both eyes
This is treated as inherited until proven otherwise. Almost every child with retinoblastoma in both eyes carries the fault in every cell. Testing is still done, because the exact fault is what the family needs for testing siblings.
One eye, several tumours
More than one separate tumour in a single eye raises the chance that the fault is inherited. The second eye is watched closely while the result is awaited.
One eye, one tumour, no family history
This is the most common picture, and most of these children do not have the inherited kind. A smaller group do, which is why every child is offered testing rather than being reassured on looks alone.
Points to the inherited kind
- Diagnosis in the first months of life
- A parent or relative who had an eye removed as a child
- A tumour found later in the second eye
A parent who had retinoblastoma
If a parent had it in both eyes, or already knows they carry the fault, each child has a one in two chance of inheriting it. The family fault is already known, so testing a new baby is quick and targeted.
Not sure whether this applies to you?
Ask an oncologistHow the test answers it
What happens between the diagnosis and the answer?
Counselling first
A genetic counsellor draws your family tree, including both parents' sides, and explains what each possible result would mean for your other children.
The tumour, if an eye was removed
When an eye has been removed, the tumour is tested first. It shows both damaged copies of RB1, so the laboratory knows exactly what to look for next.
The blood sample
The child's blood is then checked for those same faults. Found in the blood means inherited. Absent from the blood lowers the chance a great deal, though it does not remove it completely.
Parents and siblings
If the child carries the fault, both parents and every brother and sister are tested for that one exact change. Those results decide who needs eye examinations and who can stop.
On your report
The words you will meet, in plain language
- RB1
- The gene that normally stops cells in the retina from growing out of control. Both copies must be broken for a tumour to form.
- Heritable retinoblastoma
- The kind where one faulty copy is in every cell. It can be passed to children and carries a lifelong raised risk of other cancers.
- Germline
- Present in every cell from birth, including egg or sperm cells. This is what a blood test is looking for.
- De novo
- A new fault that first appeared in this child. Neither parent carries it, but the child can still pass it on.
- Mosaic
- A fault present in some cells but not all, because it arose very early in the pregnancy. A blood test can miss it.
- Penetrance
- How often a fault actually leads to tumours. For most RB1 faults this is high, but some rare faults cause fewer or milder tumours.
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Side by side
What each result changes for your family
Inherited kind confirmed
No fault found in the blood
The other eye is examined closely for years
The other eye is still checked, less intensively
Brothers and sisters are tested for the exact fault
Siblings' risk falls close to that of any child
Lifelong awareness of second cancers
No raised risk of other cancers is expected
The child's own future children can be tested early
A small residual chance is discussed before they plan a family
Commonly believed
Four things parents tell us, and what is actually true
"Nobody in our family had eye cancer, so it cannot be inherited."
Most children with the inherited kind are the first in their family. The fault appeared new in that child. They can still pass it to their own children, which is why testing matters even with a blank family tree.
"Only one eye is affected, so it is not genetic."
One eye makes the inherited kind less likely, not impossible. A smaller group of children with one affected eye still carry the fault in every cell.
"We married within the family, so that must be the cause."
Cousin marriage matters for conditions that need two faulty copies from two parents. Retinoblastoma needs only one inherited faulty copy, so a consanguineous marriage does not explain it. Parents should not carry that guilt.
"Once the eye is removed, the genetic question is over."
Removing the eye treats the tumour. It does not change the child's genes. The removed tumour is in fact the most useful sample for answering the genetic question properly.
Being straight with you
What this page cannot tell you
It cannot tell you whether your child's retinoblastoma is the inherited kind. Only a test can do that, arranged by a genetic counsellor or a clinical geneticist who knows how many tumours there were, in which eyes, and what the family history looks like on both sides.
It cannot read a report you are holding
RB1 reports can describe many different kinds of change, and some are classified as uncertain. What your specific variant means is a question for the counsellor who ordered the test. Please do not search the variant name online and draw conclusions at night.
Who this does not apply to
This page is about retinoblastoma, the eye cancer of young children. It does not apply to adult eye tumours, to a squint or a white reflex that turned out to be something else, or to faults found only in a tumour elsewhere in the body. Tumour-only testing belongs with targeted therapy, not here.
Counselling can be arranged in Telugu, and a parent can bring a grandparent or an elder who will help make decisions.Questions we are asked
Common questions about whether retinoblastoma is inherited
Is retinoblastoma always genetic?
It is always caused by damage to the RB1 gene, but that damage is not always inherited. In many children it happened only inside the eye, by chance. The genetic test separates the two, and only the inherited kind affects the rest of the family.
Which parent did it come from?
Often neither. Most inherited cases are new in the child. When a parent does carry the fault, testing both parents for the child's exact change shows which one. It is nobody's fault either way, and a parent could not have known or prevented it.
Why test the tumour if we already have a blood test?
The tumour holds both damaged copies of RB1. Once the laboratory knows those two faults, it can search the blood for them precisely. This gives a far more reliable answer than a blood test done blind, especially for a child with one affected eye.
Can a blood test miss the inherited kind?
Rarely, yes. If the fault arose very early in the pregnancy, it may be in some cells and not others, and may not show in blood. This is why a negative result lowers risk a great deal without taking it to zero. Your counsellor will explain what remains.
Our baby has a new brother or sister. What now?
If the affected child's fault is known, the new baby can be tested for it soon after birth. Until the result is back, eye examinations usually begin in the first weeks. Tell the eye team about the pregnancy early so the plan is ready.
Will our child's own children be affected?
If your child has the inherited kind, each of their children has a one in two chance of inheriting the fault. That is a conversation for when they are an adult, and there are choices around pregnancy and early testing that a counsellor can explain then.
What if the result is uncertain?
A variant of uncertain significance means a change was found but nobody yet knows whether it breaks the gene. It is not treated as a positive result. Siblings are usually examined as a precaution, and the result is reviewed as evidence builds.
Where do we start in Hyderabad?
Ask the eye cancer team treating your child whether RB1 testing has been sent, and whether any removed tumour was stored for it. Bring every report to a genetic counsellor. Call the CION helpline if you are unsure where to go, 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) — Retinoblastoma
- MedlinePlus Genetics — Retinoblastoma
- MedlinePlus Genetics — RB1 gene
- National Cancer Institute — Retinoblastoma Treatment (PDQ) – Patient 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.
Keep reading
Related pages
Screening a newborn siblingWhat happens for a baby brother or sister, from the first weeksExamination under anaesthesia for screeningHow the eye checks are actually done in small childrenLifelong second cancer riskWhat the inherited kind means after childhoodUnilateral vs bilateral retinoblastomaWhat one eye or both eyes says about the gene
Talk to us
Has anyone told you whether RB1 testing was sent?
Bring your child's reports and tell us who else is in the family. We will help you find a genetic counsellor and explain what the test can and cannot answer. One helpline serves every CION centre.