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CION Cancer Clinics
RET testing in babies and toddlers: when and why | CION Cancer Clinics
If a parent carries a RET fault, their babies and toddlers are usually tested early. That is unusual for a cancer gene. Thyroid cancer linked to RET can start in childhood, and timely surgery prevents it. This page explains when testing is advised for each risk level, what the test involves for a small child, and what happens next if your child carries the fault. 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
- Should a baby or toddler be tested for RET?
- What happens for a child at each risk level?
- How does testing a young child actually work?
- Terms from your child's clinic, in plain language
- Testing early or waiting: what changes?
- What this page cannot tell you
- Four things parents worry about
- Common questions about testing a young child for RET
The short answer
Should a baby or toddler be tested for RET?
Yes, if a parent carries a RET fault. RET is one of the few genes that doctors test in young children, because the thyroid cancer it causes can begin in childhood and early surgery prevents it. The age for testing depends on the family's exact variant, so it is planned with a counsellor.
Why most gene tests wait, and why RET does not
For most inherited cancer genes, testing waits until the child is an adult and can choose. Nothing useful happens in childhood, so there is no reason to decide on their behalf. RET is different. A child who carries it needs thyroid surgery before cancer forms, and for some variants that means within the first year of life. Knowing early is what protects them.
What the test involves for a small child
A small blood sample is usually enough, and some laboratories accept a cheek swab. There is no fasting and no special preparation. The laboratory looks only for the change already found in the parent, so the result is clear and simple to read. Sit with your child during the sample, and bring a feed or a favourite toy.
A child who does not carry the family change needs no further RET checks, and cannot pass it on.It depends on the variant
What happens for a child at each risk level?
International thyroid guidelines group RET variants by risk. The group decides when a child is tested and when surgery is advised.
Highest risk
Usually the change behind MEN2B. Testing is advised soon after birth. Guidelines advise thyroid surgery within the first year of life, by a surgeon experienced with infants.
Early signs of MEN2B
- Constipation or feeding trouble from birth
- Crying without tears
- Small bumps on the lips or tongue
High risk
Several MEN2A changes fall here. Children are tested early, and surgery is usually advised at or before about five years of age, guided by calcitonin results. If calcitonin rises sooner, surgery is brought forward. Adrenal checks begin later in childhood.
Moderate risk
Checks with calcitonin and a neck ultrasound usually begin around the age of five. Surgery is planned when calcitonin starts to rise.
Some families prefer
- Surgery in childhood rather than years of checks
- Discussing both paths with the team
Tested negative
The child's thyroid risk is the same as any other child's. No calcitonin tests, no scans and no surgery are needed for RET.
Not sure whether this applies to you?
Ask an oncologistStep by step
How does testing a young child actually work?
Counselling for the parents
Ideally during pregnancy or soon after birth. The counsellor checks the family variant and agrees when the child should be tested.
The sample
A small blood sample or cheek swab, taken at a clinic. It can often be collected nearer home and sent to the laboratory.
The result, explained to you
A counsellor goes through it in person or by video. You will not be left to read a report on your own.
A paediatric endocrinologist sees a carrier child
They measure calcitonin and plan a neck ultrasound. Calcitonin is naturally higher in babies, so it must be read by a team used to children.
Surgery is planned
The whole thyroid is removed by a surgeon who operates on children often. Daily thyroid hormone starts afterwards.
Words you will hear
Terms from your child's clinic, in plain language
- Targeted test
- A test for the one change already found in the parent. It is quicker and simpler than reading the whole gene.
- Paediatric endocrinologist
- A children's hormone specialist. They follow your child's thyroid, growth and calcium.
- Calcitonin
- A hormone from the thyroid C cells. A rising level is the earliest sign of change.
- Preventive thyroidectomy
- Removing the whole thyroid before cancer forms, or while any cancer is still tiny and inside the gland.
- Parathyroid glands
- Tiny glands beside the thyroid that control calcium. Surgeons take great care to protect them.
- Thyroxine
- The daily thyroid hormone tablet or liquid. The dose grows with the child.
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Side by side
Testing early or waiting: what changes?
Tested at the advised age
Testing put off
Surgery timed before cancer forms
Cancer may start before anyone knows
Usually a smaller operation
Neck glands may need removing too
A negative result ends the worry early
Years of not knowing
Checks planned calmly
Decisions made in a hurry later
Being straight with you
What this page cannot tell you
It cannot tell you the right age for your child. That depends on the exact variant, your child's calcitonin results and the surgeon's view. What your specific variant means is a question for the counsellor who ordered the test.
It cannot remove the worry about surgery
Thyroid surgery in a small child carries real risks, mainly to the calcium glands and the voice nerves. These risks are lower in the hands of a surgeon who operates on children often. Ask the surgeon how many such operations they do, and what happens if calcium runs low afterwards.
Who this does not apply to
Children in families with other cancer genes, such as BRCA1 or BRCA2, are usually not tested until adult life. Children of a parent whose RET change was found only in a tumour, such as a lung cancer, do not need a test. That change is not inherited.
If a baby has constipation from birth, cannot make tears or has small bumps on the lips, mention MEN2B to the paediatrician.Commonly believed
Four things parents worry about
"A baby is too small for a gene test."
A very small sample is enough. The test looks for one known change, and the process is no harder than a routine blood test.
"We will wait until she is old enough to decide."
For most genes that is right. For RET, waiting past the advised age lets cancer start, and she may not get the chance to decide at all.
"He looks healthy, so he cannot have it."
Children who carry most RET changes look and feel completely well. Only a test can tell. A healthy child is exactly who early testing protects.
"Only the boys need testing. They carry the family line."
Daughters and sons have the same one in two chance. A daughter who carries RET needs the same care and can pass it on in the same way.
Questions we are asked
Common questions about testing a young child for RET
Will my child grow normally without a thyroid?
Yes, with daily thyroid hormone. The dose is checked with blood tests and raised as the child grows. Children on the right dose grow, learn and play normally. Missing doses is the main thing to avoid.
Can RET be tested before birth?
Yes. Testing during pregnancy, or choosing an embryo through IVF, is possible when the family change is known. These choices are personal. Discuss them with a counsellor well before or early in a pregnancy.
Can the sample be taken in our district?
Often, yes. Many laboratories collect samples locally and send them on. The counselling before and after the test is best done with a genetics team, in person or by video.
Does my child need to fast before the test?
No. A gene test is not affected by food. Feed your baby as usual. Calcitonin tests later on may have their own instructions, which the clinic will give you.
What will we tell our child when they are older?
Tell them in simple words, a little at a time, as they grow. Teenagers should know about the gene before they marry or plan a family. A counsellor can help you plan that conversation.
What if my child tests negative but the other one is positive?
That is common, since each child has their own separate chance. The negative child needs nothing further for RET. Be careful how the difference is talked about at home, so neither child feels singled out.
Who pays for testing children?
A test for a known family change usually costs less than the parent's first test. Ask the clinic for a written estimate. Check with the billing desk whether any scheme covers the test or the surgery.
Where do we start?
Find the parent's RET report. Book a counselling visit and ask when your child should be tested. Call the CION helpline if you are not sure which clinic to approach.
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
- American Thyroid Association (Thyroid, via PubMed) — Revised American Thyroid Association guidelines for the management of medullary thyroid carcinoma
- GeneReviews (NCBI) — Multiple Endocrine Neoplasia Type 2
- National Cancer Institute — Genetics of Endocrine and Neuroendocrine Neoplasias (PDQ)
- MedlinePlus Genetics — Multiple endocrine neoplasia
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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Wondering when your child should be tested?
Tell us the parent's RET result and your child's age. We will help you arrange counselling and the right test at the right time. One helpline serves every CION centre.