The thyroid gland
The thyroid is a small gland in the front of the neck just below the voice box (larynx), and is made up of two parts, or lobes. It is one of a network of glands throughout the body that make up the endocrine system. This system is responsible for producing the body's hormones that help to control and influence various functions.
The thyroid is sometimes known as the 'activity' gland because it produces the two main hormones, thyroxine (T4) and triiodothyronine (T3), which are needed to keep the body functioning at its normal rate. In order to produce the thyroid hormones, the thyroid gland needs a regular supply of iodine (which is found in fish, seafood and dairy products).
The thyroid gland
If the levels of T3 and T4 in the blood fall, the hypothalamus (a part of the brain) sends out thyroid- releasing hormone (TRH) into the blood. As the levels of TRH in the blood rise, the pituitary gland releases thyroid-stimulating hormone (TSH) which stimulates the thyroid to produce more thyroid hormones.
If the thyroid gland doesn't produce enough hormones you will feel tired and lethargic and put on weight easily. This is called hypothyroidism, or myxoedema. If the thyroid gland produces too much hormone you will lose weight, have an increased appetite, feel shaky and anxious, or have palpitations. This is known as hyperthyroidism, or thyrotoxicosis.
What is cancer?
The organs and tissues of the body are made up of tiny building blocks called cells. Cancer is a disease of these cells.
Cells in different parts of the body may look and work differently but most reproduce themselves in the same way. Cells are constantly becoming old and dying, and new cells are produced to replace them. Normally, cells divide in an orderly and controlled manner. If for some reason the process gets out of control, the cells carry on dividing, developing into a lump which is called a tumour.
Tumours can be either benign or malignant. Cancer is the name given to a malignant tumour. Doctors can tell if a tumour is benign or malignant by examining a small sample of cells under a microscope. This is called a biopsy.
In a benign tumour the cells do not spread to other parts of the body and so are not cancerous. However, if they continue to grow at the original site, they may cause a problem by pressing on the surrounding organs.
A malignant tumour consists of cancer cells that have the ability to spread beyond the original area. If the tumour is left untreated, it may spread into and destroy surrounding tissue. Sometimes cells break away from the original (primary) cancer. They may spread to other organs in the body through the bloodstream or lymphatic system.
The lymphatic system is part of the immune system - the body's natural defence against infection and disease. It is a complex system made up of organs, such as bone marrow, the thymus, the spleen, and lymph nodes. The lymph nodes (or glands) throughout the body are connected by a network of tiny lymphatic ducts.
When the cancer cells reach a new area they may go on dividing and form a new tumour. This is known as a secondary cancer or metastasis.
It is important to realise that cancer is not a single disease with a single type of treatment. There are more than 200 different kinds of cancer, each with its own name and treatment.
Types of cancer
The majority of cancers, about 85% (85 in a 100), are carcinomas. They start in the epithelium, which is the covering (or lining) of organs and of the body (the skin). The common forms of breast, lung, prostate and bowel cancer are all carcinomas.
Carcinomas are named after the type of epithelial cell that they started in and the part of the body that is affected. There are four different types of epithelial cells:
A cancer that starts in squamous cells is called a squamous cell carcinoma. A cancer that starts in glandular cells is called an adenocarcinoma. Cancers that start in transitional cells are transitional cell carcinomas, and those that start in basal cells are basal cell carcinomas.
Leukaemias and lymphomas
These occur in the tissues where white blood cells (which fight infection in the body) are formed, i.e. the bone marrow and lymphatic system. Leukaemia and lymphoma are quite rare and make up about 6.5% (6.5 in 100) of all cancers.
Sarcomas are very rare. They are a group of cancers that form in the connective or supportive tissues of the body such as muscle, bone and fatty tissue. They account for less than 1% (1 in 100) of cancers.
Sarcomas are split into two main types:
Others forms of cancer
Brain tumours and other very rare forms of cancer make up the remainder of cancers.
Each year, approximately 1500 people in the UK are diagnosed with thyroid cancer. It is a rare cancer that is most likely to affect people who are middle-aged or older. However, one type of thyroid cancer (papillary) can occur in people younger than this. Thyroid cancer is more common in women. It is very rare in children.
By examining cells from the cancer, your doctor will be able to tell which type you have, and the best type of treatment for you. There are four main types of cancer of the thyroid:
These two types are sometimes called differentiated thyroid cancer and they are often treated in the same way.
It is also possible to have a lymphoma of the thyroid gland. This is another rare type of thyroid cancer, which starts in the lymph tissue of the thyroid. The lymph tissue is part of the body's lymphatic system. Usually thyroid lymphomas are a type of non-Hodgkin lymphoma (NHL).
Apart from the anaplastic type and lymphoma, cancer of the thyroid tends to develop very slowly, and it may be some years before it starts to cause any problems. With treatment, the outlook for most people with cancer of the thyroid is very good and many people are completely cured, even if the cancer has spread beyond the thyroid.
Risk factors and causes of thyroid cancer
The exact causes of thyroid cancer in most people are not known, but research is going on all the time to try to find the cause. There are a number of risk factors that can increase your chance of developing thyroid cancer. These are:
Benign thyroid disease
People who have certain non-cancerous (benign) thyroid diseases are more likely to develop thyroid cancer. These include:
The more common thyroid conditions of an over- or under-active thyroid (hyperthyroidism and hypothyroidism) do not increase your risk of developing thyroid cancer.
A poor diet that contains large amounts of butter, cheese and meat may increase your risk of developing thyroid cancer. Large amounts of fresh fruit and vegetables may help to reduce your risk.
Low iodine levels
People who eat very little iodine in their diet are more likely to develop thyroid cancer. You are more likely to have a low iodine level if you are also exposed to radiation or if you have a history of benign thyroid disease.
Iodine is found in the soil and if you live in an area where the levels of iodine are low, the levels in your drinking water, and any locally grown vegetables or reared animals will also be low.
Inherited faulty gene
In a very small number of people, medullary thyroid cancer may be due to an inherited faulty gene. The affected gene is the RET gene. There are two main types of inherited condition in which this occurs:
Family members of someone with medullary thyroid cancer can be tested to see if they have inherited an abnormal RET gene. If someone is found to have the abnormal gene they may be advised to have their thyroid gland removed to prevent cancer developing. This is known as a prophylactic thyroidectomy.
There is also an increased risk of developing thyroid cancer if you have the inherited bowel condition called familial adenomatous polyposis (FAP).
Exposure to radiation
This may be due to radiotherapy given in childhood, or to unusually high levels of radiation in the environment; for example, in the areas surrounding Chernobyl in the Ukraine, following the nuclear power explosion of 1986. Thyroid cancer can develop many years after exposure. However, only a small number of thyroid cancers are caused by radiation exposure.