In most cases, the exact cause of thyroid cancer is unknown.

However, there are a number of risk factors that can increase your chances of developing the condition, including having another thyroid condition and being exposed to radiation (see below).

How cancer begins

Cancer begins with an alteration to the structure of deoxyribonucleic acid (DNA), found in all human cells. This is known as a genetic mutation. The DNA provides the cells with a basic set of instructions, such as when to grow and reproduce.

The mutation in the DNA changes these instructions, causing the cells to keep growing. This results in them reproducing uncontrollably which causes a lump of tissue (tumour) to form.

How cancer spreads

Left untreated, cancer can spread to the other parts of the body, usually through the lymphatic system. The lymphatic system is similar to the blood circulation system. It is made up of a network of vessels and glands (lymph nodes) distributed throughout the body.

The lymph nodes produce many of the specialised cells needed by your immune system (the body’s natural defence system against infection and illness).

Once the cancer reaches your lymphatic system, it is 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 are 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

The five main risk factors for developing thyroid cancer are:

• thyroid conditions
• radiation exposure
• inherited genetic mutations
• diet
• gender

These are discussed below.

Thyroid conditions

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).

Around one in five thyroid cancer cases occur in people who have had a previous benign thyroid condition.

Having an overactive thyroid gland (hyperthyroidism) or an underactive thyroid gland (hypothyroidism), does not increase your chances of developing thyroid cancer.

Radiation exposure

Exposure to radiation during childhood is another risk factor identified with thyroid cancer. Two types of radiation exposure are associated with thyroid cancer. They are:

• nuclear fall-out
• radiation used for medical treatments

Nuclear fall-out is radioactive waste released during a nuclear explosion. It can also occur when a nuclear reactor malfunctions, releasing high levels of nuclear waste into the atmosphere.

Many recently reported cases of thyroid cancer are thought to have been caused by radiation exposure during medical procedures that occurred between 1910-1960. 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. This will hopefully lead to a decrease in the number of thyroid cancer cases in the future.

Inherited genetic mutations

Inherited genetic mutations are responsible for a small number of medullary thyroid carcinomas.

If the instructions carried in genes (the smallest unit of genetic material) are altered, some of the body’s processes will not work normally. In medullary thyroid carcinomas, the affected gene is known as the RET gene.

The two types of inherited condition where the mutation occurs are:

• familial medullary thyroid cancer (FMTC) – which affects many family members
• multiple endocrine neoplasia (MEN) syndrome, types 2A and 2B – where family members can develop a number of different endocrine tumours including medullary thyroid cancer

In cases of MEN2A or MEN2B thyroid cancer, the mutations usually develop in childhood or during the teenage years. In FMTC, the mutations usually develop in adulthood.

In FMTC, MEN2A and MEN2B, the gene mutations are passed on through autosomal dominant inheritance. This means that if either of your parents has one of the mutations that causes thyroid cancer, you have a one in two chance of also being born with the affected gene.

If one of your parents has a history of medullary thyroid carcinoma or MEN syndrome, you should consider having a blood test to find whether you have the mutated genes. If your test results are positive, it will usually be recommended that your thyroid gland is surgically removed as a precaution.

Diet

If your diet contains low levels of the trace element, iodine, you are at increased risk of developing thyroid cancer.

People exposed to radiation, or those with a history of benign thyroid conditions (see above), 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. You can use the BMI healthy weight calculator to find out what your body mass index is.

Gender

Women are around two-and-a-half times more likely to develop thyroid cancer than men. It is thought this may be due to hormones released during a woman’s monthly period or during pregnancy. However, there is little scientific evidence to support this theory.

Unfortunately, cancerous cells can return many years after surgery and radioactive iodine treatment has been completed.

It is 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 experience a return of cancerous cells in other parts of their body, such as their bones.

Due to the risk of cancer cells returning, you will be asked to attend regular check-ups so any cancerous cells that do return can be quickly treated.

Thyroglobulin testing

Thyroglobulin testing is the main method used 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 have had your thyroid gland removed, there should be no thyroglobulin present in your blood, unless cancerous cells have returned.

Therefore, 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 surgery, you will probably need to have thyroglobulin testing every six months. After this time, testing will be required once a year.

Other tests

Other tests that may be used to check for the reoccurrence of cancerous cells include:

• an ultrasound scan of the neck
• a radioactive iodine scan

These tests are described below. 

Ultrasound scan

An ultrasound scanner uses high frequency sound waves to create an image of part of the inside of the body. Ultrasound scans can be a useful way of detecting any changes or abnormalities inside your neck that could indicate the recurrence of cancer.

Ultrasound scans are increasingly being used in combination with thyroglobulin testing because research suggests it is an effective method of detecting recurring thyroid cancer.

Radioactive iodine scan

After having surgery to remove part or all of your thyroid gland, you may be asked to attend a radioactive iodine scanning test.

The test involves swallowing a small amount of radioactive iodine before your body is scanned using a special camera. The radioactive iodine will highlight any cancerous thyroid cells remaining in your body.

The preparation for an iodine scan is similar to having radioactive iodine treatment. You will need to go on a low iodine diet and stop taking your thyroid hormone medication. Alternatively, recombinant human thyroid stimulating hormone (rhTSH) can be used without having to interrupt your thyroid hormone medication.

As the dose of radioactive iodine used for the scan is very small, no precautions, such as keeping your distance from others, are required. However, if you think you may be pregnant, or if you are breastfeeding, you must let the doctors know before your test.

A radioactive iodine scan will usually be carried out six to eight months after surgery. If the test results are negative, further testing is not usually required.

A thyroid function test and a procedure known as fine-needle aspiration cytology are used to help diagnose thyroid cancer.

If you have any possible symptoms of thyroid cancer, your GP will examine your neck and ask about any associated symptoms you may be experiencing, such as unexplained hoarseness.

The next step is to check whether the swelling in your neck is caused by other problems with your thyroid gland. This is done by carrying out a blood test known as a thyroid function test.

Thyroid function test

The most common cause of swelling in the neck is either an overactive thyroid gland (hyperthyroidism) or an underactive thyroid gland (hypothyroidism). A thyroid function test will help confirm or rule out these conditions.

A thyroid function test measures the amount of certain types of hormones in your blood. Excess levels of the two hormones produced by the thyroid gland, thyroxine and triiodothyronine, indicate an underlying condition that is making your thyroid gland overactive.

If your thyroid gland is underactive, another gland, known as the pituitary gland, will produce a hormone called thyroid stimulating hormone (TSH). TSH is released by your body to stimulate your thyroid gland. Therefore, if you have a high level of TSH in your blood it means your thyroid gland is underactive.

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. FNAC is an outpatient procedure, which means you will not have to spend the night in hospital.

A small needle will be inserted into the lump in your neck to allow a small sample of cells to be removed. The sample will be studied under a microscope. FNAC can usually reveal whether or not any cancerous cells are present in your thyroid gland and, if they are, what type of thyroid cancer you have.

Further testing

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 CT scan or MRI scan

In most cases, when it has not been possible to rule out thyroid cancer by FNAC, surgery will be recommended to remove the part of the thyroid gland that contains the lump or swelling.

Staging

Staging is a way of assessing how far the cancer has spread through the body – the higher the grade, the further it has spread.

It is usually impossible to stage the tumour before the initial treatment has been completed – that is, after surgery and radioactive iodine treatment (see below).

Thyroid cancer can be categorised using a system known as TNM classification, where:

• T – indicates the size of the tumour
• N – indicates whether the cancer has spread to nearby lymph nodes (small glands that remove unwanted bacteria from the body)
• M – indicates whether the cancer has spread to other parts of the body (metastasis)

While widely used, the TNM classification system can sometimes be difficult for someone with little or no medical knowledge to understand. Therefore, the rest of this topic will use a staging system derived from TNM, where the stages of thyroid cancer are described numerically.

Staging for differentiated thyroid cancers (papillary carcinomas and follicular carcinomas) varies with a person’s age because in older people these types of cancers tend to be more aggressive.

Only two stages are used for differentiated thyroid cancers in people under 45 years of age. They are:

• stage 1 – the cancer may have spread to other lymph nodes in the neck or head, but not to other parts of the body
• stage 2 – where the cancer has spread to other parts of the body

Four stages are used in cases of differentiated thyroid cancers that occur in people over 45 years of age, and for all cases of medullary thyroid carcinoma. They are:

• stage 1 – the tumour is no larger than 2cm (0.79 inches) across and has not spread beyond the thyroid gland
• stage 2 – the tumour is now 2-4cm (0.79-1.57 inches) across but is still contained within the thyroid gland
• stage 3 – the tumour has spread out of the thyroid gland into nearby lymph nodes
• stage 4A – the tumour has spread out of the lymph nodes and into other tissues in the neck, such as the muscles, or has spread to the lymph nodes in the upper chest, but not to other parts of the body
• stage 4B – the tumour has spread to the tissue near the spine but not to other parts of the body
• stage 4C – the tumour has spread to other parts of the body; usually the bones, the lungs or both

Staging is not usually used for cases of anaplastic thyroid carcinoma because by the time it is diagnosed, the cancer will have spread to another part of the body.

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 thyroid cancer is a painless lump or swelling that develops in your neck.

Other symptoms only tend to occur after the condition has reached an advanced stage and may include:

• unexplained hoarseness
• difficulty breathing and swallowing
• pain in your neck

Read more about the symptoms of thyroid cancer.

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 human body).

The thyroid gland releases three separate hormones. They are:

• triiodothyronine, known as T3
• thyroxine, known as T4
• calcitonin

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).

Excess T3 and T4 will make you feel overactive and you may lose weight. If you do not have enough of these hormones you will 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 is not 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 four out of five cases; it usually affects people under 40 years of age, particularly women
• follicular carcinoma – accounts for around one in 10 cases of thyroid cancer and tends to affect older adults
• medullary thyroid carcinoma – accounts for around one in 20 cases; unlike the other types of thyroid cancer, medullary thyroid carcinoma can run in families
• anaplastic thyroid carcinoma – is the rarest and most aggressive type of thyroid cancer, accounting for one in 100 cases; most cases affect older people aged 60-80 years

Papillary and follicular carcinomas are sometimes known as differentiated thyroid cancers (DTCs), and they are often treated in the same way.

What causes thyroid cancer?

In most cases, the cause of thyroid cancer is unknown. However, there are risk factors that can increase your chances of developing the condition.

Risk factors for thyroid cancer include:

• having a benign (non-cancerous) thyroid condition
• inheriting a faulty gene (in the case of medullary thyroid cancer)
• radiation exposure

Read more about the causes of thyroid cancer.

Diagnosing thyroid cancer

Your GP will examine your neck and ask whether you have any associated symptoms, such as unexplained hoarseness.

The next step will be to check whether the swelling in your neck is being caused by other thyroid problems. This will involve having a type of blood test, known as a thyroid function test, to measure the hormone levels in your blood.

Fine-needle aspiration cytology (FNAC) is the next stage in diagnosing thyroid cancer. Further testing may be required if the FNAC results are inconclusive, or if more information is needed to make your treatment more effective.

Read more about how thyroid cancer is diagnosed.

Treating thyroid cancer

Your recommended treatment plan will depend on the type and grade of your cancer, and if a complete cure is realistically achievable.

Most differentiated thyroid cancers (DTCs) – papillary and follicular carcinomas – and some medullary thyroid carcinomas are thought to have a good prospect of achieving a cure.

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. Lymph nodes are small, oval-shaped glands that remove unwanted bacteria and particles from the body. Radiotherapy iodine treatment is not used because it is ineffective in treating this type of thyroid cancer.

Read more about treating thyroid cancer.

Recurrence

Cancerous cells will return in an estimated 5-20% of people with a history of thyroid cancer. Approximately 10-15% of people will experience a return of cancerous cells in other parts of their body, such as their bones.

Sometimes, cancerous cells can return many years after surgery and radioactive iodine treatment has been completed. Due to this risk, you will be asked to attend regular check-ups so any cancerous cells that do return can be quickly treated.

Read more about the complications of thyroid cancer.

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, with plenty of fresh fruit and vegetables (at least five portions a day) and wholegrains.

Outlook

The outlook for the differentiated thyroid cancers (DTCs) 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 (see above).

More than nine out of 10 people with papillary carcinoma will live for 10 or more years after diagnosis. More than eight out of 10 people with follicular thyroid cancer will live at least 10 years after being diagnosed.

Medullary thyroid carcinoma is harder to treat. This type of thyroid cancer does not 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, the outlook is excellent, with 97% of people living at least five years after diagnosis.

However, if medullary thyroid carcinoma is diagnosed after it has spread to other parts of the body, the outlook is poor – only one in four people live at least five years after diagnosis.

Due to its aggressive nature, the outlook for anaplastic thyroid carcinoma is very poor. Fewer than one in 10 people will live at least five years after being diagnosed, with the average survival time being eight months.

In its early stages, thyroid cancer tends to cause no or very few symptoms.

The main symptom of cancer of the thyroid 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 are much smaller and less prominent than a man’s.

Sometimes, the lymph nodes in your neck can also be affected and become swollen. Lymph nodes are small glands that form part of the lymphatic system which filters blood, drains fluid from tissues back into the bloodstream, and helps fight infections.

Other symptoms of thyroid cancer only tend to occur after the condition has reached an advanced stage. These symptoms may include:

• unexplained hoarseness
• difficulty swallowing
• difficulty breathing
• pain in your neck

When to seek medical advice

You should always visit your GP if you develop a swelling or lump at the front of your neck. Although it is unlikely to be the result of thyroid cancer, it is important that you have it investigated, just in case.

About one in 20 swellings or lumps in the neck that are large enough to be felt or seen are due to thyroid cancer. Most cases are caused by non-cancerous swellings called goitres.

Goitres

A goitre is an enlarged thyroid gland. The thyroid gland can become enlarged due to one or more multiple swellings (nodules) within the gland.

Non-cancerous goitres are usually caused by other, less serious problems with your thyroid gland, such as the thyroid gland:

• producing too much of the triiodothyronine (T3) and thyroxine (T4) hormones – this is known as having an overactive thyroid gland or hyperthyroidism
• not producing enough T3 and T4 hormones – this is known as having an underactive thyroid gland or hypothyroidism

If you are diagnosed with thyroid cancer, you will 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 (see below).

Cancer treatment team

All NHS hospitals have multidisciplinary teams (MDTs) who treat thyroid cancer. An MDT is made up of a number of different specialists and may include:

• a surgeon
• 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 serve as your first point of contact with the rest of the team

If you have thyroid cancer, you may see some or all of these people as part of your treatment.

It can be difficult to decide on the best course of treatment for you. Your cancer team will make recommendations based on reviewing your individual 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.

Questions to ask at your doctor’s appointment.

Your treatment plan

The treatment recommended for you 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 (DTCs) – papillary carcinomas and follicular carcinomas – and some cases of medullary thyroid carcinomas have a good prospect of achieving a cure.

DTCs are treated using a combination of:

• surgery to remove your thyroid gland (thyroidectomy)
• a type of radiotherapy called radioactive iodine treatment, designed to destroy any remaining cancer cells and prevent the thyroid cancer returning

Medullary thyroid carcinomas tend to spread faster than DTCs, so it may be necessary to remove your thyroid gland and any nearby lymph nodes (small glands that remove unwanted bacteria from the body). Radiotherapy iodine treatment is not used because it is ineffective in treating this type of thyroid cancer.

Stage 4 medullary thyroid carcinomas are not 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 is not usually achievable. This is because by the time the condition has been diagnosed, it has usually spread to other parts of the body, such as the windpipe and lungs.

Radiotherapy and chemotherapy can be used to slow the progression of anaplastic thyroid carcinoma and it can 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.

This involves medication being used to directly target the cancerous cells (see below). However, these types of treatments are currently undergoing clinical trials and are not offered routinely on the NHS.

Thyroidectomy

In almost all cases of thyroid cancer, it will be necessary to remove some of your thyroid gland (a hemithyroidectomy) or all of your thyroid gland (a total thyroidectomy).

The decision to remove some or all of your thyroid gland will be influenced by a number of factors, including:

• 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 will explain to you the type of surgery required and why it is required, so that you can make an informed decision.

A thyroidectomy will be carried out under a general anaesthetic. The operation usually takes around two hours and will leave a small scar on your neck which will not be very noticeable.

For the first 24-48 hours after surgery, you will be connected to a series of drips to provide fluids and help speed up the healing process.

As your neck will feel sore, you will be given painkillers to help ease any discomfort. Your voice may sound hoarse, but this usually passes within a few weeks. However, in a small number of cases, the hoarseness can be permanent.

After having a thyroidectomy, swallowing food may be painful for a number of weeks. You may need to switch to a diet of soft food until your neck recovers from the surgery. A nurse or dietitian will be able to give you dietary advice.

Most people are well enough to leave hospital three to five days after having thyroid surgery. However, you will 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 MDT will be able to advise you about when you will be healthy and 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 will experience symptoms of an underactive thyroid (hypothyroidism) such as fatigue, weight gain and dry skin.

To compensate for the removal of your thyroid gland, you will need to take replacement hormone tablets for the rest of your life.

If your surgery is to be followed by radioactive iodine treatment, it is likely that initially you will be given a hormone tablet called triiodothyronine.

After radioactive iodine treatment is completed, you will be prescribed an alternative hormone tablet called thyroxine, which most people only need to take once a day.

You will need to have regular blood tests to check you are 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 the optimum dose is achieved, 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. Once the right dose has been achieved, you should not experience any more side effects.

Calcium levels

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 during surgery, 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 because 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 are taking thyroid hormone replacement tablets, you will 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.

After you have stopped taking your thyroid hormone replacement tablets, you may feel very tired and weak, but these symptoms will pass once you begin taking the tablets again.

If it is thought that withdrawing your hormone replacement treatment could be particularly problematic, you may be given a medicine called recombinant human thyroid stimulating hormone (rhTSH). This is given as an injection on two consecutive days.

The main advantage of having rhTSH is that you will not need to interrupt your thyroid hormone replacement treatment. However, rhTSH may not be suitable for you for a number of reasons. Your MDT will be able to advise you about whether or not rhTSH is suitable for you.

The procedure

Radioactive iodine treatment involves swallowing radioactive iodine in either liquid or capsule form. The radiation contained in the iodine will travel up into your neck through your blood supply and destroy 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 some people have an altered taste and dry mouth permanently.

Following radioactive iodine treatment, you will need to stay in hospital for three to five days because the iodine will make your body slightly radioactive. As a precaution, you will need to stay in a single room, protected by lead sheets, so that hospital staff are not exposed to radiation.

You will not be able to have visitors during this time, and pregnant women and children will not be allowed to visit you while you are in hospital because they are more vulnerable to the effects of radiation. Hospital staff will also keep their contact with you to a minimum during this time.

Your bodily fluids, such as urine, will be slightly radioactive for three to five days after your treatment, so it is important that you flush the toilet every time you use it. Your sweat will also be radioactive so you should bath or shower every day.

Once the radioactive levels in your body have subsided, you will be allowed home.

Dietary recommendations

While having radioactive iodine treatment, you will need to eat a diet low in iodine. A diet rich in iodine may reduce the effectiveness of your treatment. It is recommended that you:

• avoid all seafood
• limit the amount of dairy products you eat 
• do not eat glace and maraschino cherries because they contain colouring (E127) that is high in iodine
• do not take cough medicines or use sea salt because they both contain iodine

Eat plenty of fresh meat, fresh fruit and vegetables, and pasta and rice. They are all low in iodine.

Pregnancy and breastfeeding

You should not have radioactive iodine treatment if you are pregnant, or if there is a good chance that you may be. The treatment could damage your baby. Tell your MDT if you are unsure whether you are pregnant. Any treatment will need to be delayed until after your pregnancy.

If you are not pregnant, you will still need to use a reliable method of contraception for at least six months after having iodine treatment. This is because there is a small risk that any child conceived during this time could develop birth defects.

A similar risk applies to men, who should use a reliable method of contraception for at least four months after having iodine treatment.

Your MDT will be able to advise you about when it is safe for you to try to conceive a child.

If you are breastfeeding, you should stop for at least four weeks (but preferably eight) before starting iodine treatment, and you should not resume until after your treatment has finished. It is safe for you to breastfeed if you have another child in the future.

Fertility

Radioactive iodine treatment does not affect fertility in women. However, there is a small risk that it could affect fertility in men who need to undergo multiple treatment sessions. Your MDT will be able to advise about the level of risk in your individual circumstances.

If there is a significant risk you will 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

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 will need to have radiotherapy for will depend on the particular type of thyroid cancer you have and its progression.

Side effects of radiotherapy include:

• nausea (feeling sick)
• vomiting
• tiredness
• pain on swallowing
• dry mouth

These side effects should pass two to three weeks after your course of radiotherapy has finished.

Chemotherapy

Chemotherapy is usually only used to treat anaplastic thyroid carcinomas that have spread to other parts of your body.

Chemotherapy involves taking powerful medicines that kill cancerous cells. It is rarely successful in curing anaplastic cancer, but can slow its progression and help relieve symptoms.

Possible side effects of chemotherapy include:

• nausea
• vomiting
• tiredness
• loss of appetite
• hair loss 
• mouth ulcers

If you are receiving chemotherapy, you will also be more vulnerable to infection. See your GP if you suddenly feel ill or your temperature rises above 38^oC (100.4^oF).

Targeted therapies

A number of targeted therapies are being tested in clinical trials (a type of research that tests one treatment against another) to treat advanced cases of:

• medullary thyroid cancers
• differentiated thyroid cancers (DTCs) that do not respond to radioactive iodine
• anaplastic thyroid carcinomas

In targeted therapies, medication which specifically targets the biological functions that cancers need to grow and spread, is used.

As research into targeted therapies for thyroid cancer is ongoing, some medications used in this type of treatment are unlicensed. This means the medication has not been issued with a license for use in treating thyroid cancer.

In exceptional circumstances, your specialist may suggest using an unlicensed medication. They will do this if:

• they think it is 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 will tell you that it is unlicensed and will discuss 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).

Find your local CCG.