Thyroid cancer

What is cancer?

A lump of human tissue the size of a sugar cube may contain a thousand million cells. These are the minute building blocks from which our bodies are made, visible only down the microscope. It is quite amazing that the billions of cells in a human body normally function in perfect harmony, every cell knowing its place and doing the job that it was designed to do. Most cells have a finite lifespan: millions of new ones are produced every day to replace those lost through old age or wear and tear.

New cells are produced when existing cells divide into two. Except in children, who are growing, there is normally a perfect balance between the numbers of the cells that are dying and those that are dividing. Normally exactly the right amounts of new cells are produced to replace those that are being lost. The control mechanisms involved are exceedingly complex. Loss of control can lead to an excess of cells, resulting in a tumour.

However, it is important to realise that only a very small minority of tumours are cancerous. Most tumours are localised accumulations of normal or fairly normal cells and are benign. A wart is a common example.

The development of a cancer (malignant tumour) involves a change in the quality of the cells as well as an increase in quantity: they change in both appearance and behaviour. They become more aggressive, destructive and independent of normal cells. They acquire the ability to infiltrate and invade the surrounding tissues.

In some instances the cells may also invade lymphatic and blood vessels and thus spread away from the ‘primary’ growth to other places. In time these cells may cause the development of secondary growths, known as ‘metastases’, in the lymph glands and other organs such as lungs, liver and bones. Malignant tumours of the thyroid gland are rare. For example, a specialist may see 50 to 100 patients with hyperthyroidism caused by Graves’ disease for every one with thyroid cancer. The types of cancer that doctors see most frequently are:

•    Papillary cancer which usually affects children and young women.

•    Follicular cancer which is unusual before the age of 30.

These terms describe the appearance of the tumour under the microscope. In papillary cancer, the tumour contains papillae or fronds, whereas in follicular cancer, although the appearance is distinctly abnormal, there are still structures that resemble the normal follicles of the thyroid. Both cancers can occur at any age, however.

Provided that diagnosis and treatment are at an early stage, the person may well live out a normal lifespan; in other words, you’re still more likely to die of a stroke or a heart attack in old age.

Confirming the diagnosis

Most patients visit their GP with a lump in the neck or because of rapid growth of a goitre that they’ve had for many years. The diagnosis of thyroid cancer is made at a hospital visit by fine needle aspiration or following surgery.

Occasionally, the patient consults his or her doctor because of enlarged lymph nodes in the neck which may at first be thought to be caused by Hodgkin’s disease. However, a biopsy shows that the patient actually has papillary cancer which has spread from the thyroid gland via the lymphatic system to the nearby lymph nodes.

Treatment

Surgery

Both papillary and follicular cancers are usually treated by removing as much of the thyroid gland as possible (total thyroidectomy). Any enlarged lymph nodes in the neck containing thyroid cancer are also removed at this stage.

No special treatment is required before the operation and you can usually go home after two days. As a result of the extent of the surgery, damage to the parathyroid glands is more common than in other thyroid surgery. The low level of calcium in the blood that results is easily treated by taking a vitamin D derivative, known as alfacalcidol (One-Alpha), in a dose of one to two micrograms each day by mouth.

Radioactive iodine

It is not possible to remove every last part of the thyroid gland by means of surgery. For this reason, most patients with papillary or follicular cancer will be given a large dose of radioactive iodine (iodine-131) to kill any remaining cells.

The radioactive iodine is given as a liquid or a capsule in hospital. You will have to stay in hospital for 48 to 72 hours, in a single room, separated from the other patients.

The radioactive iodine is usually given three to four weeks after your operation and before thyroxine tablets have been started, as it is most effective when the patient is hypothyroid and TSH levels in the blood are high. If for some reason there is a delay, and you have already started taking thyroxine to prevent you from becoming hypothyroid after removal of your thyroid gland, you will be taken off the treatment some four weeks before being given the radioactive iodine.

Towards the end of the period without thyroxine you may feel tired but will come to no harm. The thyroxine can be re-started in full dosage 48 hours after your treatment and you will feel your normal self after another 10 to 14 days. An alternative to stopping thyroxine is for Thyrogen to be given by intramuscular injection on each of the two days before the iodine-131 treatment.

Thyroxine

Doctors believe that the rate of growth of papillary and follicular cancers of the thyroid may be increased by the hormone TSH. An important part of the treatment, therefore, is to make sure that you take enough thyroxine to ensure that the level of TSH in your blood becomes undetectable.

Patients with thyroid cancer need a slightly greater dose of thyroxine than those with hypothyroidism. A dose of 150 to 200 micrograms daily is usually sufficient to switch off TSH secretion by the pituitary gland.

Follow-up

Papillary and follicular cancers, like the normal thyroid gland, make a substance called thyroglobulin.

The thyroid gland can secrete this substance only in the presence of TSH, but this is not the case with thyroid cancer. So, if there is no TSH detectable in the bloodstream because it has been suppressed by treatment with thyroxine, any thyroglobulin in the blood must be coming from recurrent cancer in the neck or from cancer that has spread to other parts of the body (secondaries or metastases).

Thyroglobulin is known as a ‘tumour marker’. If a patient who is taking appropriate amounts of thyroxine has a raised level of thyroglobulin, the specialist may wish to arrange other tests such as an ultrasound of the neck, or a CT scan of the chest to identify the site of the recurrent tumour or its metastases.

Scanning of the whole body using radioactive iodine may also be helpful. The scan is usually performed 24 to 48 hours after a dose of iodine-131 by mouth, four weeks after the patient has stopped taking thyroxine or after TSH injections.

Any tumour that is found may be treated with a large dose of radioactive iodine in hospital.

Thyrogen

This is the name given to recombinant human TSH, a protein identical to TSH in the pituitary gland and blood, but which has been made in the laboratory. It has recently become available in the UK. Thyrogen (thyrotropin alfa) can be given as an intramuscular injection on each of two successive days before treatment with radioactive iodine.

By increasing the TSH concentrations in the blood in this way, you will not need to stop your thyroxine tablets for four weeks and will not suffer any of the symptoms of an underactive thyroid gland.

About a year after your treatment by surgery and radioactive iodine, your specialist may wish to measure the tumour marker, thyroglobulin, before and after two Thyrogen injections so that he or she can find out whether your thyroid cancer has been cured, or whether any other treatment may be needed.

Outlook

This depends upon the size of the tumour and whether it has spread at the time of diagnosis. If treated correctly, a young woman with a small papillary cancer of the thyroid is likely to have a normal life expectancy, despite the cancer having spread to the lymph nodes in the neck. Even patients with follicular cancer that has spread to the bones or lungs may survive for many years with a good quality of life.

Case history: Susan

Susan Jones was 18 when she fell heavily while skating, striking the side of her neck against the ice-rink barrier. As the pain and bruising settled she noticed a pea-sized lump in her neck. To begin with her doctor thought that it must be related to the accident, although it moved when she swallowed, suggesting that it lay within the thyroid gland rather than in the skin or muscle.

When it hadn’t disappeared after six weeks, he referred Susan to a thyroid specialist at the local teaching hospital. The consultant examined Susan’s neck carefully and found that, in addition to the single small thyroid nodule, there were three enlarged lymph nodes on the right side of her neck. He proceeded to take a tiny sample from the thyroid nodule and from one of the lymph nodes, sucking out cells with a syringe and needle. The test took only a few minutes, causing Susan no discomfort and with no need even for a local anaesthetic.

The next day Susan and her mother were told that the sample showed that the lump in Susan’s neck was a type of cancer of the thyroid, known as papillary carcinoma, and that it had spread to the nearby lymph nodes. The only treatment was an operation and two weeks later Susan was admitted to hospital where almost all of her thyroid gland was removed, together with the enlarged lymph nodes. Careful inspection of the removed gland by the pathologists showed no other signs of thyroid cancer apart from the original swelling. After the operation, Susan was treated with radioactive iodine to ensure that any remaining thyroid cells had been destroyed.

Susan has been cured and simply needs to take thyroxine tablets for the rest of her life and see the specialist every year for a blood test. The skating accident was a blessing in disguise as it brought to light a thyroid cancer which was at a very early stage. The fact that it had spread to the lymph nodes in the neck was of no consequence.

Rarer cancers

These include the following:

•    Medullary cancer of the thyroid which can occur on its own or may run in families in association with abnormalities of other endocrine glands or of the skeleton.

•    Lymphoma of the thyroid which usually affects elderly people and may be accompanied by evidence of disease in other parts of the body.

•    Anaplastic cancer which also affects elderly people.

The future prospects for people with these types of cancer is less good than for those with papillary or follicular cancer. Treatment is more difficult and may include chemotherapy and radiotherapy.

KEY POINTS

• Remember that thyroid cancer is rare

• The two types that doctors see most often – papillary and follicular cancers – can normally be treated successfully if they are caught early enough

• An operation is necessary to remove as much of the thyroid gland as possible and any abnormal lymph nodes in the neck, followed by treatment with radioactive iodine to destroy any remaining cells

• After surgery, patients will need to take thyroxine in slightly higher doses than normal

• A blood test will probably be done after treatment to make sure that there is no trace of cancer remaining and to check that it hasn’t spread

• There are a few very rare cancers which mainly affect elderly people in whom treatment may be more difficult