Medical Oncologist
CION Cancer Clinics
The RET gene: what it does and why a fault matters | CION Cancer Clinics
RET is a gene that tells certain thyroid, adrenal and nerve cells when to grow. An inherited fault jams that signal on and causes MEN2, in which medullary thyroid cancer is expected unless the thyroid is removed early. This page explains what the gene normally does, what a fault changes, and why RET is one of the few cancer genes tested in young children. 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 RET gene actually do?
- Which conditions does an inherited RET fault cause?
- How does a jammed RET switch lead to thyroid cancer?
- The words you will meet, in plain language
- How is RET different from other inherited cancer genes?
- What this page cannot tell you
- Four things families say about RET, and what is true
- Common questions about the RET gene
The short answer
What does the RET gene actually do?
RET carries the instructions for a switch on the surface of certain cells. When the right signal arrives, the switch turns on and tells the cell to grow. It matters most while a baby is forming in the womb, when it helps build the kidneys and the nerves that run the bowel.
The cells that depend on it
In adult life RET stays active in a small group of cells. These are the C cells of the thyroid, which make a hormone called calcitonin, the adrenal glands above the kidneys, and some nerve cells. These are exactly the places where an inherited RET fault causes trouble.
Why RET is unusual among cancer genes
Most inherited cancer genes work like brakes, and a fault removes the brake. RET works like an accelerator, and an inherited fault jams it on. One faulty copy is enough to send the grow signal all the time. That is why the effect on the thyroid is so predictable, and why doctors plan around it years before any cancer appears.
A RET fault is found by a simple blood test. What it means for your family is a question for the counsellor who ordered it.Three patterns
Which conditions does an inherited RET fault cause?
A RET fault causes a condition called multiple endocrine neoplasia type 2, or MEN2. It shows up in families in three main ways.
MEN2A
The most common form. Almost everyone who carries it develops medullary thyroid cancer if the thyroid is left in place.
Can also bring
- Adrenal gland tumours that release adrenaline-like hormones
- Overactive parathyroid glands and a high blood calcium
MEN2B
Rarer and earlier. The thyroid cancer can begin in infancy. Many children also have small bumps on the lips and tongue, a tall, slim build and bowel troubles as babies.
These signs are often the first clue in a family with no known history.Thyroid cancer only
Some families see medullary thyroid cancer across generations and nothing else. Doctors now treat this as a milder form of MEN2A, so the adrenal checks still continue.
A different fault, a different illness
Faults that switch RET off, rather than on, cause Hirschsprung disease, where part of the bowel has no nerves. A few rare variants do both, so the laboratory reads the exact variant carefully.
Not sure whether this applies to you?
Ask an oncologistFrom gene to cancer
How does a jammed RET switch lead to thyroid cancer?
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The fault is present from birth
It sits in every cell of the body. Most cells ignore it because they do not use RET. The thyroid C cells do.
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The C cells keep being told to grow
With the switch stuck on, the C cells slowly multiply. Doctors call this C-cell hyperplasia. It is not cancer yet, and it causes no symptoms.
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Calcitonin rises in the blood
More C cells make more calcitonin. A rising calcitonin level is the earliest sign a blood test can pick up, long before a lump.
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A small cancer forms inside the thyroid
This is medullary thyroid cancer. It behaves differently from the common kinds of thyroid cancer and does not respond to radioactive iodine.
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It can reach the neck glands quietly
It may spread to lymph nodes before anyone feels a lump. That is why surgery is timed by the gene result and calcitonin, not by symptoms.
On your report
The words you will meet, in plain language
- Germline
- Present in every cell from birth, and so it can be passed to children. A fault found only inside a tumour is called somatic.
- Pathogenic variant
- A spelling change in the gene known to cause disease. This is what people mean by a RET mutation.
- Codon
- The exact spot in the gene where the change sits. With RET the codon decides how early surgery is advised.
- Medullary thyroid cancer
- A cancer of the thyroid C cells. It is rare, and it is the cancer an inherited RET fault is known for.
- Calcitonin
- A hormone made by the C cells. It is measured in the blood to track what the thyroid is doing.
- Phaeochromocytoma
- A usually non-cancerous adrenal tumour that releases bursts of adrenaline-like hormones, which can raise blood pressure sharply.
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Side by side
How is RET different from other inherited cancer genes?
RET
Most other inherited cancer genes
An accelerator jammed on
A brake that has failed
Thyroid cancer expected in nearly all carriers
Risk raised, but far from certain
Testing offered in early childhood
Testing usually waits for adult life
The exact codon sets the timing
The gene name matters most
Preventive thyroid surgery is standard
Preventive surgery is one option among several
Being straight with you
What this page cannot tell you
It cannot tell you what your family's variant means. RET variants are graded by risk, and the grade decides when a child should have surgery and when adrenal checks begin. That reading belongs to a genetic counsellor and an endocrine team who have your report in front of them.
It cannot tell you whether a thyroid lump is RET-related
Most thyroid cancers are the common papillary kind and have nothing to do with RET. Only medullary thyroid cancer points towards RET. Anyone diagnosed with it should be offered a germline RET test, even with no family history.
Who this does not apply to
If RET appeared on a tumour report, for example in lung cancer, it is usually a change inside the tumour only. It is not inherited and guides drug choice instead, which is covered under targeted therapy. Most people with thyroid nodules do not need this test at all.
Not sure which kind of RET result you have? Call the helpline and read out the heading of the report.Commonly believed
Four things families say about RET, and what is true
"Only people with a lump in the neck need to worry."
Medullary thyroid cancer can spread to the neck glands before any lump appears. Carriers are watched with calcitonin tests so that surgery happens before that stage.
"Father's cancer was treated, so the family is safe now."
Treatment removed his cancer. It did not change his genes. Each of his children still has a one in two chance of carrying the same fault and should be offered the family test.
"RET on my lung cancer report means my children are at risk."
Almost always not. RET changes in lung cancer are found inside the tumour only. They are not in the rest of the body and cannot be passed on.
"Once the thyroid is out, RET is finished with us."
The thyroid risk ends, but adrenal checks carry on, and parathyroid checks too in MEN2A. Thyroid hormone tablets are also taken every day for life.
Questions we are asked
Common questions about the RET gene
Is a RET fault the same as having cancer?
No. It means the thyroid is very likely to develop cancer if nothing is done. That is why carriers have the thyroid removed early, often in childhood, so that the cancer never gets the chance to form or spread.
How is RET passed down in a family?
A parent with the fault has a one in two chance of passing it to each child, son or daughter alike. It does not skip generations. A child who does not inherit it cannot pass it on and needs no special checks.
Can a RET fault appear with no family history?
Yes. This happens most often in MEN2B, where many children have the first fault in the family. It also happens when a parent carried the fault quietly, or when relatives died young of something else.
Why does the exact codon matter so much?
Different spots in the gene carry different levels of risk. The highest-risk change leads to cancer in infancy, while others act more slowly. Guidelines use the codon to decide when surgery is advised and when adrenal checks begin.
What test finds a RET fault?
A blood or saliva sample is enough. The first person in a family is usually tested for the whole gene. Relatives are then tested for that one known change, which is quicker and simpler to read.
Is RET the same gene used for lung cancer drugs?
It is the same gene, but a different kind of change. In lung cancer, RET is broken inside the tumour and guides targeted drugs. The inherited change behind MEN2 is in every cell and runs in families.
Does a RET fault affect pregnancy?
It can. An unrecognised adrenal tumour can make labour and surgery dangerous, so women who carry RET are usually checked for one before or early in pregnancy. Plan this with your endocrine team and your obstetrician together.
Where do we start if medullary thyroid cancer is in the family?
Ask whether the person with the cancer has had a germline RET test. If they have, bring the report to a genetic counsellor. If they have not, that test comes first, and the CION helpline can 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
- GeneReviews (NCBI) — Multiple Endocrine Neoplasia Type 2
- MedlinePlus Genetics — RET gene
- MedlinePlus Genetics — Multiple endocrine neoplasia
- National Cancer Institute — Genetics of Endocrine and Neuroendocrine Neoplasias (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
RET codon and risk levelWhy the exact variant decides the timing of surgeryRET positive: what happens nextThe first months after a positive resultTesting the family for RETWho should be tested, and in what orderFamilial medullary thyroid cancer without full MEN2When thyroid cancer is the only pattern in the family
Talk to us
Has someone in your family had medullary thyroid cancer?
Tell us who was diagnosed and whether they have had a RET test. We will help you work out whether a genetic referral makes sense and arrange it if it does. One helpline serves every CION centre.