Thyroid cancer is a rare type of cancer that affects the thyroid gland, a small gland at the base of the neck.
The most common symptom of cancer of the thyroid is a painless lump or swelling that develops in the neck.
Other symptoms only tend to occur after the condition has reached an advanced stage, and may include:
unexplained hoarseness that lasts for more than a few weeks
a sore throat or difficulty swallowing that doesn't get better
a lump elsewhere in your neck
It's important to remember that if you have a lump in your thyroid gland, it doesn't necessarily mean you have thyroid cancer. About 1 in 20 thyroid lumps are cancerous.
The thyroid gland
The thyroid gland consists of two lobes located on either side of the windpipe. Its main purpose is to release hormones (chemicals that have powerful effects on many different functions of the body).
The thyroid gland releases three separate hormones:
triiodothyronine – known as T3
thyroxine – known as T4
The T3 and T4 hormones help regulate the body's metabolic rate (the rate at which the various processes in the body work, such as how quickly calories are burnt).
An excess of T3 and T4 will make you feel overactive and you may lose weight. If you don't have enough of these hormones, you'll feel sluggish and you may gain weight.
Calcitonin helps control blood calcium levels. Calcium is a mineral that performs a number of important functions, such as building strong bones.
Calcitonin isn't essential for maintaining good health because your body also has other ways of controlling calcium.
Types of thyroid cancer
There are four main types of thyroid cancer. They are:
papillary carcinoma – this is the most common type, accounting for about 6 out of 10 (60%) cases; it usually affects people under the age of 40, particularly women
follicular carcinoma – accounts for around 3 out of 20 (15%) cases of thyroid cancer and tends to affect older adults
medullary thyroid carcinoma – accounts for between 5 and 8 out of every 100 diagnosed cases (5-8%); unlike the other types of thyroid cancer, medullary thyroid carcinoma can run in families
anaplastic thyroid carcinoma – this is the rarest and most aggressive type of thyroid cancer, accounting for less than 1 in 20 thyroid cancers; it usually affects older people over the age of 60
Papillary and follicular carcinomas are sometimes known as differentiated thyroid cancers, and they're often treated in the same way.
How common is thyroid cancer?
Thyroid cancer is a rare form of cancer, accounting for less than 1% of all cancer cases in the UK. Each year, around 2,700 people are diagnosed with thyroid cancer in the UK.
It's most common in people aged 35 to 39 years and in those aged 70 years or over.
Women are two to three times more likely to develop thyroid cancer than men. It's unclear why this is, but it may be a result of the hormonal changes associated with the female reproductive system.
What causes thyroid cancer?
In most cases, the cause of thyroid cancer is unknown. However, certain things can increase your chances of developing the condition.
Risk factors for thyroid cancer include:
having a benign (non-cancerous) thyroid condition
having a family history of thyroid cancer (in the case of medullary thyroid cancer)
having a bowel condition known as familial adenomatous polyposis
acromegaly – a rare condition where the body produces too much growth hormone
having a previous benign (non-cancerous) breast condition
weight and height
Diagnosing thyroid cancer
A type of blood test known as a thyroid function test will measure the hormone levels in your blood and rule out or confirm other thyroid problems.
If nothing else seems to be causing the lump in your thyroid, fine-needle aspiration cytology (FNAC) is used.
Further testing may be required if the FNAC results are inconclusive, or if more information is needed to make your treatment more effective.
Treating thyroid cancer
Your recommended treatment plan will depend on the type and grade of your cancer, and whether a complete cure is realistically achievable.
Differentiated thyroid cancers (DTCs) are treated using a combination of surgery to remove the thyroid gland (thyroidectomy) and a type of radiotherapy that destroys any remaining cancer cells and prevents the thyroid cancer returning.
Medullary thyroid carcinomas tend to spread faster than DTCs, so it may be necessary to remove any nearby lymph nodes, as well as your thyroid gland.
Cancerous cells will return in an estimated 5-20% of people with a history of thyroid cancer. In approximately 10-15% of people the cancerous cells will come back in other parts of their body, such as their bones.
Cancerous cells can sometimes return many years after surgery and radioactive iodine treatment has been completed.
You'll be asked to attend regular check-ups so any cancerous cells that return can be treated quickly.
Preventing thyroid cancer
From the available evidence, eating a healthy, balanced diet is the best way to avoid getting thyroid cancer and all other types of cancer.
A low-fat, high-fibre diet is recommended that includes plenty of fresh fruit and vegetables (at least five portions a day) and whole grains.
The outlook for differentiated thyroid cancers is very good. Most people (80-90%) will have a normal lifespan.
Papillary and follicular carcinomas tend to be slow growing and relatively straightforward to treat.
More than 9 out of 10 people with papillary carcinoma will live for 10 or more years after diagnosis. More than 8 out of 10 people with follicular thyroid cancer will live for at least 10 years after being diagnosed.
Medullary thyroid carcinoma is harder to treat. It doesn't respond to iodine treatment, so removing all of the cancerous cells can be difficult.
Survival rates for medullary thyroid carcinoma depend on the stage of the cancer when it was diagnosed. If diagnosed in its early stages, 97% of people live at least five years after diagnosis.
If medullary thyroid carcinoma is diagnosed after it has spread to other parts of the body, 1 in 4 people live at least five years after diagnosis.
Because of its aggressive nature, less than 1 in 10 people with anaplastic thyroid carcinoma will live at least five years after being diagnosed.
Symptoms of thyroid cancer
In its early stages, thyroid cancer tends to cause no or very few symptoms.
The main symptom of thyroid cancer is a lump or swelling at the front of the neck just below your Adam's apple, which is usually painless.
Women also have Adam's apples, but they're much smaller and less prominent than a man's.
The lymph nodes in your neck can also be affected and become swollen. Lymph nodes are small glands that are part of the lymphatic system, which helps fight infection.
Other symptoms of thyroid cancer only tend to occur after the condition has reached an advanced stage, and may include:
unexplained hoarseness that doesn't get better after a few weeks
a sore throat or difficulty swallowing that doesn't get better
pain in your neck
When to seek medical advice
You should always see your GP if you develop a swelling or lump at the front of your neck. Although it's unlikely to be thyroid cancer, it's important that it is investigated.
About 1 in 20 swellings or lumps in the neck are caused by thyroid cancer. Most cases are caused by non-cancerous swellings called goitres.
A goitre is an enlarged thyroid gland. Non-cancerous goitres are usually caused by other less serious problems with your thyroid gland, such as:
too much triiodothyronine (T3) and thyroxine (T4) hormones – this is known as having an overactive thyroid gland, or hyperthyroidism
not enough T3 and T4 hormones – this is known as having an underactive thyroid gland, or hypothyroidism
Thyroid cancer support
The Butterfly Thyroid Cancer Trust provides information, advice and support for people with thyroid cancer.
As well as the website, they also have a helpline number that can be contacted on 01207 545469, Monday to Friday, 10am to 4pm.
Causes of thyroid cancer
In most cases, the exact cause of thyroid cancer is unknown.
However, there are a certain things that can increase your chances of developing the condition, including having another thyroid condition and being exposed to radiation.
What is cancer?
Cancer begins with a change (mutation) in the structure of the DNA in cells, which can affect how they grow. This means cells grow and reproduce uncontrollably, producing a lump of tissue called a tumour.
Left untreated, cancer can spread to other parts of the body, usually through the lymphatic system. The lymphatic system is made up of a network of vessels and glands (lymph nodes) located throughout the body.
Lymph nodes produce many of the cells needed by your immune system (the body's natural defence system against infection and illness).
Once the cancer reaches your lymphatic system, it's capable of spreading to other parts of your body, including your blood, bones and organs.
The most common types of thyroid cancer are papillary carcinomas and follicular carcinomas, which are known as differentiated thyroid cancers (DTCs).
They spread much more slowly than other types of cancer. When DTCs are diagnosed, they're usually limited to the thyroid gland itself or nearby lymph nodes.
The rarer types of thyroid cancer are more aggressive and spread faster. By the time medullary thyroid carcinoma is diagnosed, it may have spread to the lymph nodes. In advanced cases, it may have also spread to the bones and lungs.
Anaplastic thyroid cancer often spreads to the windpipe and, in some cases, the lungs.
Risk factors for thyroid cancer
The main risk factors for developing thyroid cancer are:
having a thyroid condition
having a family history of thyroid cancer (in the case of medullary thyroid cancer)
having a bowel condition known as familial adenomatous polyposis (FAP)
acromegaly (a rare condition where the body produces too much growth hormone)
having previous benign (non-cancerous) breast conditions
weight and height
These are discussed below.
Your risk of developing thyroid cancer is slightly increased if you have certain non-cancerous (benign) thyroid conditions, such as an inflamed thyroid gland (thyroiditis) or an enlarged thyroid gland (goitre).
Having an overactive thyroid gland (hyperthyroidism) or an underactive thyroid gland (hypothyroidism) doesn't increase your chances of developing thyroid cancer.
Around one in five cases of thyroid cancer occur in people who've had a previous benign thyroid condition.
Inherited genetic mutations are responsible for a small number of medullary thyroid carcinomas. If the instructions carried in genes are altered, some of the body's processes won't work normally.
This inherited mutation occurs in:
familial medullary thyroid cancer
multiple endocrine neoplasia (MEN) syndrome, types 2A and 2B
In cases of MEN2A or MEN2B thyroid cancer, the mutations usually develop during childhood or the teenage years. In familial medullary thyroid cancer, the mutations usually develop in adulthood.
If one of your parents has a history of medullary thyroid carcinoma or MEN syndrome, you should consider having a blood test to find out whether you have the mutated genes. If your test results are positive, it's recommended you have surgery to remove your thyroid gland as a precaution.
Familial adenomatous polyposis
If you have a bowel condition called familial adenomatous polyposis (FAP), your risk of developing thyroid cancer is increased. FAP runs in families and is caused by inheriting a faulty gene.
Find out more about FAP on the Cancer Research UK website.
Thyroid cancer risk is increased in people who have acromegaly. This is a rare condition where the body produces too much growth hormone.
Previous breast conditions
If you've had a benign (non-cancerous) breast condition in the past, such as a breast cyst or fibroadenoma (non-cancerous tumour), your risk of developing thyroid cancer increases by around half (50%) compared with women who haven't had this type of condition.
Weight and height
If you're overweight, you're more at risk of developing thyroid cancer than someone who isn't overweight.
Research has also shown that taller adults have an increased risk. However, the reasons for this are unclear.
Exposure to radiation during childhood is another risk factor for thyroid cancer.
Radiation from nuclear fallout and radiation used for medical treatments have both been associated with thyroid cancer.
Many recently reported cases of thyroid cancer are thought to have been caused by radiation exposure during medical procedures carried out between 1910 and 1960.
During this time, not much was known about the risks of radiation treatment. Today there are much stricter regulations regarding the use of radiation for medical procedures.
Other risk factors
If your diet contains low levels of the trace element iodine, you're at an increased risk of developing thyroid cancer.
People exposed to radiation, or those with a history of benign thyroid conditions, are more likely to have low levels of iodine.
Eating a lot of butter, cheese and meat may also increase your risk of developing thyroid cancer. To help reduce your risk, you should include plenty of fresh fruit and vegetables in your diet.
People with a high body mass index (BMI) also have an increased risk of developing thyroid cancer. Use the BMI healthy weight calculator to find out what your body mass index is.
Women are about two to three times more likely to develop thyroid cancer than men.
It's thought this may be because of the hormones released during a woman's monthly period or during pregnancy. However, there's little scientific evidence to support this theory.
The Cancer Research UK website has more information about women's risk of thyroid cancer.
Diagnosing thyroid cancer
For many people, the first stage of diagnosing thyroid cancer is a consultation with a GP.
Your GP will examine your neck and ask about any associated symptoms you may be experiencing, such as unexplained hoarseness.
Thyroid function test
A blood test known as a thyroid function test is used to check whether the swelling in your neck is caused by other problems with your thyroid gland.
It will rule out conditions such as an overactive thyroid gland (hyperthyroidism) or an underactive thyroid gland (hypothyroidism), which are the most common thyroid problems.
A thyroid function test measures the amount of certain types of hormones in your blood.
Further tests will be needed if the thyroid function test reveals your thyroid gland is working normally.
Fine-needle aspiration cytology
Fine-needle aspiration cytology (FNAC) is the next stage in diagnosing thyroid cancer. It's an outpatient procedure, which means you won't have to spend the night in hospital.
A small needle is inserted into the lump in your neck to allow a tiny sample of cells to be removed. The sample is then studied under a microscope.
This test can usually reveal whether cancerous cells are present in your thyroid gland and, if they are, what type of thyroid cancer you have.
Further testing may be recommended if the FNAC results are inconclusive or if further information is needed to make your treatment more effective. These tests may include:
repeat FNAC combined with an ultrasound scan
other types of scan, such as a computerised tomography (CT) scan or magnetic resonance imaging (MRI) scan
In most cases, surgery will be recommended to remove the part of the thyroid gland that contains the lump or swelling when it hasn't been possible to rule out thyroid cancer.
Treating thyroid cancer
If you're diagnosed with thyroid cancer, you'll be assigned a care team, who will devise a treatment plan for you.
Your recommended treatment plan will depend on the type and grade of your cancer, and whether your care team thinks that a complete cure is realistically achievable.
Cancer treatment team
An MDT is made up of a number of different specialists, and may include:
an endocrinologist (a specialist in treating hormonal conditions)
an oncologist (a cancer treatment specialist)
a pathologist (a specialist in diseased tissue)
a radiotherapist or clinical oncologist (a specialist in non-surgical methods of treating cancer, such as chemotherapy and radiotherapy)
a specialist cancer nurse, who will usually be your first point of contact with the rest of the team
Deciding on the best course of treatment can be difficult. Your cancer team will make recommendations after reviewing your case, but the final decision will be yours.
Before you go to hospital to discuss your treatment options, you may want to write a list of questions to ask the specialist. For example, you may want to find out what the advantages and disadvantages of particular treatments are.
Your treatment plan
Your recommended treatment will depend on a number of things, including:
the type of thyroid cancer you have
the grade of your cancer
whether your care team thinks a complete cure is realistically achievable
Most differentiated thyroid cancers – papillary carcinomas and follicular carcinomas – and some medullary thyroid carcinomas have a good prospect of achieving a cure.
Differentiated thyroid cancers are treated using a combination of:
surgery to remove your thyroid gland (thyroidectomy)
a type of radiotherapy called radioactive iodine treatment, which is designed to destroy any remaining cancer cells and prevent the thyroid cancer returning
Medullary thyroid carcinomas tend to spread faster than differentiated thyroid cancers, so it may be necessary to remove your thyroid gland and any nearby lymph nodes.
Radiotherapy iodine treatment is not effective at treating this type of thyroid cancer.
Stage 4 medullary thyroid carcinomas aren't usually curable, but it should be possible to slow their progression and control any associated symptoms.
In most cases of anaplastic thyroid carcinoma, a cure isn't usually achievable. This is because it's usually spread to other parts of the body by the time it's been diagnosed.
Radiotherapy and chemotherapy can be used to slow the progression of anaplastic thyroid carcinoma and help control any symptoms.
Some cases of differentiated thyroid cancer, medullary thyroid carcinoma and anaplastic thyroid carcinoma may benefit from a new type of treatment known as targeted therapies.
In almost all cases of thyroid cancer it's necessary to either remove some of your thyroid gland in a procedure called a hemithyroidectomy, or all of your thyroid gland (total thyroidectomy).
This decision will be influenced by:
the type of thyroid cancer you have
the size of the tumour
whether or not the cancer has spread beyond your thyroid gland
Your surgeon should discuss with you the type of surgery required and why so you can make an informed decision.
A thyroidectomy is carried out under a general anaesthetic and usually takes around two hours. The operation will leave a small scar on your neck, which shouldn't be very noticeable. In a small number of cases, it may cause permanent hoarseness.
Most people are well enough to leave hospital three to five days after having thyroid surgery. However, you'll need to rest at home for two to three weeks and avoid any activities that could put a strain on your neck, such as heavy lifting.
A member of your care team will be able to advise you about when you'll be fit enough to resume normal activities and return to work.
Replacement hormone therapy
If some or all of your thyroid gland is removed, it will no longer be able to produce the hormones that regulate your metabolic system.
This means you'll experience symptoms of an underactive thyroid (hypothyroidism), such as fatigue (extreme tiredness), weight gain and dry skin.
To compensate, you'll need to take replacement hormone tablets for the rest of your life.
If your surgery is to be followed by radioactive iodine treatment, it's likely you'll be given a hormone tablet called triiodothyronine.
After radioactive iodine treatment is completed, you'll be prescribed an alternative hormone tablet called thyroxine, which most people only need to take once a day.
You'll need to have regular blood tests to check you're receiving the right amount of hormones and to determine whether your dose needs to be adjusted.
It may take some time to achieve the optimum dose. Until this time, you may experience symptoms of tiredness or weight gain if your hormone levels are too low.
Alternatively, if your hormone levels are too high, you may experience symptoms such as weight loss, hyperactivity or diarrhoea. You shouldn't experience any more side effects once the right dose has been achieved.
Occasionally, the parathryoid glands can be affected during surgery. The parathryoid glands are located close to the thyroid gland and help regulate the levels of calcium in your blood.
If your parathryoid glands are affected, your calcium levels may decrease, which can cause a tingling sensation in your hands, fingers, lips and around your nose.
These symptoms should be reported to your MDT or GP as you may need to take calcium supplements. Most people only need to take a short course of calcium tablets as the parathryoid glands will soon start to function normally again.
Radioactive iodine treatment
After having thyroid surgery, a course of radioactive iodine treatment may be recommended. This will help destroy any remaining cancer cells in your body and prevent the cancer returning.
If you're taking thyroid hormone replacement tablets, you'll need to stop taking them for two to four weeks before having radioactive iodine treatment. This is because they can interfere with the effectiveness of the iodine treatment.
If withdrawing your hormone replacement treatment is problematic, you may be given a medicine called recombinant human thyroid stimulating hormone (rhTSH). This is given as an injection on two consecutive days.
Your MDT will be able to advise you about whether or not rhTSH is suitable for you.
Radioactive iodine treatment involves swallowing radioactive iodine in either liquid or capsule form. The radiation in the iodine travels up into your neck through your blood supply and destroys any cancerous cells.
Side effects of radioactive iodine treatment are uncommon, but a small number of people may experience tightness, pain or swelling in their neck and may feel flushed (warm). These side effects usually pass within 24 hours.
After treatment, you may have a dry mouth and notice a change in your taste. These symptoms usually disappear after a few weeks or months, although they can be permanent in some people.
You'll need to stay in hospital for three to five days after the procedure because the iodine will make your body slightly radioactive. As a precaution, you'll need to stay in a single room protected by lead sheets so that hospital staff aren't exposed to radiation.
You won't be able to have visitors during this time and hospital staff will keep their contact with you to a minimum.
Your bodily fluids, such as urine, will also be slightly radioactive for three to five days after your treatment, so it's important that you flush the toilet every time you use it. Your sweat will be radioactive, too, so you should bathe or shower every day.
You'll be allowed home after the radioactive levels in your body have subsided.
While having radioactive iodine treatment, you'll need to eat a diet low in iodine. An iodine-rich diet may reduce the effectiveness of your treatment. It's recommended that you:
avoid all seafood
limit the amount of dairy products you eat
don't take cough medicines or use sea salt as they both contain iodine
You should eat plenty of fresh meat, fresh fruit and vegetables, and pasta and rice. These are all low in iodine.
Pregnancy and breastfeeding
You shouldn't have radioactive iodine treatment if you're pregnant or if there's a good chance that you may be. The treatment could damage your baby.
Tell a member of your care team if you're unsure whether you're pregnant. Any treatment will need to be delayed until after your pregnancy.
You must stop breastfeeding before you can be treated with radioactive iodine. If possible, you should stop breastfeeding six weeks prior to treatment.
You should not resume breastfeeding after treatment for your current child, but you may safely breastfeed any babies you may have in the future.
Breastfeeding also isn't recommended while receiving iodine treatment. If you're breastfeeding, you should stop at least four weeks (but preferably eight) before starting iodine treatment.
You should also not resume breastfeeding your baby. However, it's safe for you to breastfeed if you have another child in the future.
You should use a reliable method of contraception for at least six months after having iodine treatment. This is because there's a small risk that any child conceived during this time could develop birth defects. This applies to both men and women.
Radioactive iodine treatment doesn't affect fertility in women. However, there's a small risk that it could affect fertility in men who need to have multiple treatment sessions. Your care team will be able to advise you about the level of risk in your individual circumstances.
If there's a significant risk you'll become infertile after having radioactive iodine treatment, you may wish to consider having your sperm or eggs harvested and frozen so they can be used for fertility treatment at a later date.
External radiotherapy, where radioactive waves are targeted at affected parts of the body, is usually only used to treat advanced or anaplastic thyroid carcinomas.
The length of time you'll need to have radiotherapy for will depend on the particular type of thyroid cancer you have and its progression.
Side effects of radiotherapy include:
pain when swallowing
These side effects should pass two to three weeks after your course of radiotherapy has finished.
Chemotherapy is usually only used to treat anaplastic thyroid carcinomas that have spread to other parts of your body.
It involves taking powerful medicines that kill cancerous cells. It's rarely successful in curing anaplastic cancer, but can slow its progression and help relieve symptoms.
Possible side effects of chemotherapy include:
loss of appetite
If you're receiving chemotherapy, you'll also be more vulnerable to infection. See your GP if you suddenly feel ill or your temperature rises above 38C (100.4F).
A number of targeted therapies are being tested in clinical trials to treat advanced cases of:
medullary thyroid cancers
differentiated thyroid cancers that don't respond to radioactive iodine
anaplastic thyroid carcinomas
In targeted therapies, medication specifically targets the biological functions that cancers need to grow and spread.
As research is ongoing, some medications used in this type of treatment are unlicensed. In exceptional circumstances, your specialist may suggest using an unlicensed medication. They'll do this if:
they think it's likely to be effective
there are no better alternatives
the benefits of treatment outweigh any associated risks
If your specialist is considering prescribing an unlicensed medication, they'll tell you that it's unlicensed and will discuss the possible risks and benefits with you.
The decision about whether to fund treatment with medications used in targeted therapies is often made by individual clinical commissioning groups (CCGs).
The Cancer Research UK website has more information about biological therapy for thyroid cancer.
Taking part in a clinical trial: Sheila’s story
When Sheila was diagnosed with breast cancer in 2004, her GP suggested she join a clinical trial for a new breast cancer drug. Sheila explains her decision process, how the trial was explained to her, and any doubts or safety concerns she had.
Media last reviewed: 13/06/2014
Next review due: 13/06/2016
Doctors will occasionally prescribe a medication for a use it's not licensed for. They'll only do this if they are willing to take personal responsibility for the off licence use of the treatment.
Your local clinical commissioning group (CCG) may need to be involved to decide whether to support your doctor's decision and pay for the medication from their budget.
Thyroid cancer forum
I have severe redness of my nose. I am trying a liquid product for spider…
I spotted on Health Unlocked's ' A Call To Action' community site, member…
I often think it would be extremely positive to march on Downing Street with…
Hi all. I really dont know were to start. I have been supplementing b12 5000mcg…
Hope Nicola sturgeon has had that lump on her neck checked out
More from the community
Complications of thyroid cancer
Cancerous cells can return many years after surgery and radioactive iodine treatment has been completed.
It's estimated that 5-20% of people with a history of thyroid cancer will experience a return of cancerous cells in their neck.
An estimated 10-15% of people will see a return of cancerous cells in other parts of their body, such as their bones.
Because of the risk of cancer cells returning, you'll be asked to attend regular check-ups so any cancerous cells that do return can be treated quickly.
Thyroglobulin testing is a special type of blood test that's used to monitor some types of thyroid cancer and to check for the return of cancerous cells.
Thyroglobulin is a protein released by a healthy thyroid gland, but it can also be released by cancerous cells.
If you've had your thyroid gland removed, there should be no thyroglobulin present in your blood, unless cancerous cells have returned.
Regularly testing your blood for thyroglobulin can be an effective way of checking whether or not any cancerous cells have returned.
For the first few years after having surgery you'll probably need to have thyroglobulin testing every six months. After this period, you'll need to be tested once a year.
An ultrasound scanner uses high-frequency sound waves to create an image of part of the inside of the body. An ultrasound scan can detect changes inside your neck that could indicate the recurrence of cancer.
Radioactive iodine scan
After surgery to remove part or all of your thyroid gland, you may be asked to attend a radioactive iodine scanning test.
You swallow a small amount of radioactive iodine before undergoing a scan. The radioactive iodine will highlight any cancerous thyroid cells in the body.
Before the scan, you'll need to go on a low-iodine diet and stop taking your thyroid hormone medication.
As only a small dose of radioactive iodine is used, it's not necessary to keep your distance from others. However, if you think you may be pregnant or you're breastfeeding, let the doctors know before your test.
A radioactive iodine scan will usually be carried out six to eight months after surgery.