Overview
Thyroid cancer is the 18th most common cancer in women, but is much less common in men. Each year in Europe, approximately 25,000 people will be diagnosed as having thyroid cancer. The number of new cases has increased over the past 25 years and varies considerably from country to country. For instance, Germany has 3 times more new cases of thyroid cancer each year than the UK, whilst France has twice as many cases as the UK. However, it is Iceland that has the highest incidence in Europe.
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Key Figures
| Total number of new cancer cases in Europe (2006) |
3.2 million |
| Total number of cancer deaths in Europe (2006) |
1.7 million |
| Number of new thyroid cancer cases in Europe |
25,000 per year |
| Number of thyroid cancer deaths in Europe |
6,000 per year |
The prognosis for the different types of thyroid cancer is very different (see Prognosis section below). Differentiated thyroid cancers (papillary and follicular types) have the best prognosis with a survival rate of 90% or more.
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Cancer Types
There are four different types of thyroid cancer:
- Papillary carcinoma is the most common, accounting for about 75 - 85 % of all cases, and occurs mainly in younger women. Papillary thyroid cancer is a well differentiated tumour, meaning that the tumour cells closely resemble normal thyroid cells.
- Follicular cancer tends to affect a slightly older age group, but is less common than papillary carcinoma and accounts for about 10 - 15% of all thyroid cancer cases. Hürthle cell cancer (less than 5% of all cases) is a particular form of follicular cancer that grows more rapidly than other cancers of this type. Follicular thyroid cancer is also well differentiated with tumour cells which closely resemble normal thyroid cells.
- Medullary carcinoma is rare (less than 5% of all thyroid cancers) and is sometimes hereditary.
- Anaplastic carcinoma is also uncommon. It accounts for less than 5% of all cases across Europe but there are big differences from country to country.
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Causes of Thyroid Cancer
There are a number of well known risk factors for thyroid cancer.
- Thyroid cancer is three times more common in women.
- It is most common in people aged between 20 and 60.
- Asian people are more prone to developing thyroid cancer.
- Follicular cancers are more common where diets are low in iodine, which is an essential ingredient of thyroid hormones (T4 and T3).
- Exposure to radiation is a further risk factor – patients who have been treated with radiotherapy for other conditions have an increased risk of thyroid cancer, as do people affected by nuclear fallout.
- Medullary cancer (one of the less common thyroid cancers) is inherited in approximately 20% of cases.
- Papillary and follicular thyroid cancers also occasionally run in families. However, the genetic basis for this remains unknown.
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Prevention of Thyroid Cancer
There are no practical steps that can be taken to avoid thyroid cancer. Awareness is the key - as with all cancers, the earlier the diagnosis is made the more effective treatment will be. Any lumps in or enlargement of the thyroid gland should be investigated as a matter of urgency.
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Common Symptoms
Common symptoms include:
- painless lump in the anterior or lateral aspects of the neck which gradually increases in size
- painless enlarged lymph nodes in the lateral aspects of the neck
- difficulty in swallowing
- difficulty in breathing - both due to pressure effects of an enlarged thyroid gland on the oesophagus and trachea
- hoarseness of the voice
These symptoms can also be due to other benign swellings in the thyroid gland.
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Diagnostic Tests
Suspected thyroid cancers can be investigated by obtaining a fine needle aspirate, which is then analysed under a microscope.
Ultrasound scans distinguish between solid lumps and fluid-filled cysts but cannot distinguish between benign and cancerous solid lumps.
Radioactive isotope scans detect cancers as their cells absorb less radioactive iodine than normal thyroid and so show up as “cold spots”. However, cysts and benign nodules also show as cold areas so this is not the best test to make a diagnosis.
There is no valid screening method from blood analyses.
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Treatment
Thyroid cancers must be treated using surgery, usually removing the thyroid gland altogether and so removing the cancer. Further treatment with radioactive iodine, radiotherapy or a combination of these treatments may be required to prevent local recurrence or to treat metastases.
External beam radiation is not normally used to treat follicular or papillary carcinomas of the thyroid except in specific circumstances.
Chemotherapy is not normally used in treating thyroid cancer, except for some anaplastic tumours.
Differentiated Thyroid Cancer (Papillary and Follicular Types)
Surgery
Surgery, is the main treatment. In some cases it is followed by administration of a radioactive isotope of iodine (I-131) given 4-6 weeks after surgery whilst the patient is hypothyroid. This is repeated if necessary.
Total thyroidectomy is the removal of the whole gland. Surgery is safe but after total thyroidectomy, replacement hormone tablets are needed to prevent the symptoms of hypothyroidism. The exact amount will be determined following the monitoring of blood tests. There is the possibility that the recurrent laryngeal nerve which goes to the larynx can be affected by surgery, resulting in a hoarse or weak voice. However, this side effect is rarely permanent and often responds well to speech therapy. In 14% of cases hypoparathyroidism may also occur as a consequence of total thyroidectomy. This also requires replacement therapy.
Radioactive Iodine Therapy
Radioactive iodine is used in addition to surgery in treating the papillary and follicular forms of thyroid cancer. A radioactive isotope of iodine known as Iodine131 or I-131 is given as a capsule or as a liquid. The thyroid gland is the only organ in the body that absorbs iodine and so radioactive iodine can be used to destroy (or ablate) thyroid tissue including thyroid cancer cells in papillary and follicular thyroid cancers. Radioiodine must be given 4-6 weeks after surgery to hypothyroid patients not taking any substitution therapy with T4. The recent introduction of recombinant TSH makes it possible to treat some patients, depending on their risk factors, without making them hypothyroid for weeks.
Several treatments with iodine may be needed. The first one will destroy any normal thyroid tissue which takes up iodine even more readily than do cancer cells. Subsequent doses will then be taken up by thyroid cancer cells wherever they are and therefore metastases can also be treated in this way.
For some days after treatment with radioactive iodine, patients are temporarily radioactive so precautions need to be taken to avoid exposing other people (particularly children and pregnant women) to radiation. There are regulations in all countries which specify what precautions should be taken to ensure that the exposure of others is as low as is reasonably achievable.
There are other short term side effects of radioactive iodine treatment which include:
- some tenderness of the neck
- sometimes nausea
- a dry mouth
- changes in taste
- swelling of the salivary glands
Normally the latter can be overcome by drinking plenty of fluids and sucking sweets or chewing gum.
Low-dose treatments are all that are usually required. They will have no effect on either female or male fertility but all patients are advised to avoid conception for 6 months.
Men who receive large doses of radioactive iodine – usually for the treatment of cancer that has spread to other body areas - may have a low sperm count and can sometimes become infertile as a result. Large doses of radioactive iodine also affect women’s ovaries causing irregular periods for some months after treatment.
Radioactive iodine treatment is safe and has been successfully used to treat thyroid cancer for over 50 years.
Radioactive iodine is not an alternative to surgery but a very useful additional treatment to destroy cancer cells not removed during surgery.
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Medullary and Anaplastic Thyroid Cancers
Surgery
When possible, surgery is the best treatment, removing the thyroid gland and all the nearby lymph nodes and surrounding fatty tissues. External beam radiotherapy is then given to treat any remaining or relapsing areas of cancer.
Medullary and anaplastic thyroid cancers do not take up radioactive iodine and this treatment is not suitable for these tumours.
For metastases, external beam radiation in some instances combined with chemotherapy are the main treatments.
External Beam Radiation
External beam radiation is used to treat medullary and anaplastic cancers. External beam radiotherapy and surgery are used in combination for some patients.
External beam radiation usually involves treatments given in small doses several days a week for a few weeks. The treatment itself is entirely painless but there is usually some reaction in surrounding tissues, including the skin. This results in changes to the skin and sometimes difficulty in swallowing, hoarseness of the voice and fatigue. Providing the treatment in small doses allows non-cancer cells time to recover in between treatments.
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Prognosis
The prognosis for patients with the differentiated forms of thyroid cancer (papillary or follicular cancers) is generally good. More than 90% of all patients with papillary cancer will be cured.
Prognosis is determined by a number of factors, including:
- age
- gender
- cancer type
- extent of local spread
- the presence of metastases
Favourable prognostic factors for patients with differentiated thyroid cancers include:
- being female
- being from a younger age group (less than 45 years old)
- a smaller tumour size (less than 4cm)
- papillary cancer type, including the follicular variant with a well-defined capsule or follicular cancer with minimal invasion of the capsule
- no local lymph node or blood vessel invasion or distant metastases
Less favourable prognostic factors for patients with differentiated thyroid cancer are the reverse:
- being male
- being from an older age group (age 45 years or older)
- having a more aggressive tumour type with anaplastic transformation, poorly differentiated follicular cancer or tall-cell, columnar, or diffuse sclerosing variants of papillary cancer, or Hürthle cell type
- distant metastases
- local or blood vessel invasion
- multifocal papillary cancers
- delayed or inadequate treatment
Overall differentiated thyroid carcinomas (papillary and follicular types) have the best prognosis with a 10 year survival in excess of 90%.
Medullary thyroid cancer has quite a good prognosis if diagnosed early on in the disease, with over 95% living for at least 5 years after their diagnosis. Survival rates fall as the disease advances with 40% of patients living for at least 5 years after their diagnosis.
Anaplastic thyroid cancer has a poorer prognosis with less than 10% of patients living for 5 years or more after diagnosis. If the tumour is less than 5cm in size and can be completely removed surgically 20% of patients will live for at least 5 years after diagnosis.
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Key Trends
- There has been an increasing incidence of thyroid cancer over the past 25 years but no increase in thyroid cancer deaths.
- Earlier diagnosis has led to improved results.
- Maintaining a high therapeutic success rate in differentiated thyroid cancers while improving the quality of life of patients by avoiding repeated periods of hypothyroidism.
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Current Developments
Until recently radioactive iodine could only be used if the patient is hypothyroid (which is why it is not given until 6 weeks after surgery). However, the introduction of recombinant TSH allows patients to be treated without waiting for them to become hypothyroid.
There is now an increased interest in the use of monoclonal antibodies and radiolabelled peptides in the treatment of medullary cancer which has spread to other areas of the body.
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Important Research Areas
- To reduce the burden of treatment by using less aggressive treatment for thyroid cancer. In papillary and follicular cancer to give radioactive iodine to fewer patients and not to patients in the very low risk groups (tumour less than 1cm in diameter).
- Further assessment of the current developments listed above.
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Unresolved Questions
- The genetic susceptibility to thyroid cancers, in particular the papillary and follicular types.
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