What is thyroid cancer?

Thyroid cancer occurs when abnormal cells grow uncontrollably in the thyroid tissue. These abnormal cells grow to form a cancer, which can spread to other parts of the body (metastasise). 

Macro anatomy of the thyroid.Location and anatomy of the thyroid gland. 

What is the thyroid?

The thyroid is a small gland that sits at the base of the voice box (larynx) near the windpipe (trachea). It has a right and left lobe, each connected by a thin piece of tissue in the middle, called the isthmus. It uses the mineral iodine to produce thyroid hormones, which control the body's temperature, metabolism and heart rate. 

The thyroid consists of two main cell types:

  • Follicular cells - these cells selectively absorb iodine from the blood, process it for storage as colloid (a protein-rich substance), and produce thyroid hormone, and;
  • Parafollicular cells - these cells are fewer in number and produce a chemical called calcitonin, which is involved in controlling the level of calcium in the blood. 

Behind the thyroid are four small glands called parathyroid glands, which are also involved in controlling calcium levels. 

Micro anatomy of the thyroid.Microscopic structure of the thyroid gland. 

Causes

The cause of thyroid cancer, as with other cancers, is due to damage to cellular DNA. This damage can be from a number of causes, such as inherited gene mutations or exposure to radiation; however, many causes of thyroid cancers still remain unknown.

DNA

The genetic material of all living cells and some viruses. The full name is deoxyribonucleic acid.

Gene

A unit of inheritance (heredity) of a living organism. A segment of genetic material, typically DNA, that specifies the structure of a protein or related molecules. Genes are passed on to offspring so that traits are inherited, making you who you are and what you look like.

Radiation

Energy that is emitted, such as heat, light, or energy in electromagnetic waves. Different types of radiation can be used to diagnose and treat disease.

Types

Thyroid cancer is categorised according to the type of cell it arises from. There are four main types of thyroid cancer, which include:

  • Papillary thyroid cancer - this is the most common type of thyroid cancer, originating in the follicular cells of the thyroid. It is more common in women and usually occurs before the age of 45;
  • Follicular thyroid cancer - also originates in the follicular cells of the thyroid, but grows more slowly. It usually occurs after the age of 45;
  • Medullary thyroid cancer - originates in the parafollicular cells of the thyroid that produce the calcitonin hormone. About a quarter of people with medullary thyroid cancer develop it as a result of a specific, inherited gene, which can also result in development of multiple other cancers, known as multiple endocrine neoplasia syndromes (MEN). These syndromes can result in development of benign or cancerous growths in the adrenal and parathyroid glands, and medullary thyroid cancer, and;
  • Anaplastic thyroid cancer - this is a rare and aggressive type of thyroid cancer in which the cells do not resemble normal thyroid cells.

Stages of papillary and follicular thyroid cancer (for those under 45 years)

Stage I

The cancer is of any size and may have spread to nearby tissues and lymph nodes.

Stage II

The cancer is of any size and has spread throughout the body.

Stages of papillary and follicular thyroid cancer (for those over 45 years)

Stage I

The cancer is only in the thyroid and is less than 2cm.

Stage II

The cancer is only in the thyroid and is 2-4cm.

Stage III

The cancer is:

  • Greater than 4cm and is only in the thyroid; 
  • Any size and has spread to tissues near the thyroid but not the lymph nodes, or;
  • Any size and has spread to nearby lymph nodes and may have spread to tissues near the thyroid.

Stage IV

The cancer is any size and has spread: 

  • To tissues outside the thyroid to the tracheaoesophagus, voice box (larynx) and maybe the laryngeal nerve that supplies the larynx (stage IVA); 
  • To tissue near the spinal column or the carotid artery and may have spread to the lymph nodes (stage IVB), or;
  • Throughout the body (stage IVC).

Stages of medullary thyroid cancer

Stage I

The cancer is 2cm or less.

Stage II

The cancer is greater than 2cm and is only in the thyroid, or is any size and has spread to nearby tissues but not the lymph nodes.

Stage III

The cancer is any size and has spread to the nearby lymph nodes and tissues near the thyroid.

Stage IV

The cancer is any size and has spread:

  • To tissues outside the thyroid, the trachea, oesophagus, voice box (larynx) and maybe the laryngeal nerve that supplies the larynx (stage IVA); 
  • To lymph nodes between the lungs and on one or both sides of the neck (stage IVB), or; 
  • Throughout the body (stage IVC).

Stages of anaplastic thyroid cancer

Stage IV

This type of thyroid cancer is aggressive and has usually spread by the time it is found. It can have spread:

  • To nearby tissues (stage IVA); 
  • To lymph nodes (stage IVB), or; 
  • Throughout the body (stage IVC).

Gene

A unit of inheritance (heredity) of a living organism. A segment of genetic material, typically DNA, that specifies the structure of a protein or related molecules. Genes are passed on to offspring so that traits are inherited, making you who you are and what you look like.

Lymph nodes

A small organ of the lymphatic system containing many immune cells. Lymph nodes, also known as lymph glands, are the sites where many interactions between immune cells and foreign materials occur.

Oesophagus

Also called the gullet or food pipe, it is the muscular tube connecting the throat and stomach. It is lined with a mucous membrane. After ingestion, food and drink travel down the oesophagus to be digested in the stomach.

Trachea

Also called the windpipe. A cartilaginous tube in the neck that connects the throat with the airways of the lungs.

Spinal column

The bony structure that comprises the individual vertebrae that enclose and protect the spinal cord and nerves located in the middle.

Carotid artery

A pair of main arteries in the neck that supply the head and neck with blood.

Risk factors

Risk factors for thyroid cancer include:

  • Age - the age bracket most affected is 25-65 years;
  • Gender - thyroid cancer is more common in women;
  • Radiation exposure;
  • Diet - a diet low in iodine or high in cheese, butter and meat;
  • An enlarged thyroid (goitre), and;
  • Genetics and family history - if you are Asian or have a family history of the disease or certain genetic conditions, you are more at risk.

Genetics

Related to genes, the body's units of inheritance or origin.

Iodine

A chemical element important for hormone development that is found in foods including dairy products, seafood, eggs, bread and some vegetables. It is often used in medicine as a dye.

Radiation

Energy that is emitted, such as heat, light, or energy in electromagnetic waves. Different types of radiation can be used to diagnose and treat disease.

Signs and symptoms

In the early stages, thyroid cancer may not produce any symptoms. As the condition progresses, symptoms may include:

  • A lump in the neck;
  • Difficulty breathing or swallowing;
  • A persistent cough, and;
  • A change in your voice.

There are also other medical conditions that are not cancerous that can cause one or more of these symptoms.

Methods for diagnosis 

Physical examination

Your doctor will ask you questions, take your medical history and check for signs of disease by checking your neck, larynx (voice box) and lymph nodes for presence of lumps or swelling.

Blood tests

A blood test may be performed by your doctor to measure your levels of the following:

Thyroid hormones

You may be tested for levels of thyroid-stimulating hormone (TSH). Produced in the brain, TSH stimulates thyroid follicular cell growth and triggers the production of the thyroid hormone. The thyroid hormone plays an essential role in metabolism and physical and mental development.

Thyroglobulin

Thyroglobulin is protein produced by the follicular cells and is the storage form of thyroid hormones. As thyroglobulin is only produced by the thyroid, an elevated level may be an indicator of cancer. However, as it is also raised in non-cancerous conditions, testing for it is only useful in conjunction with other information in the diagnosis of thyroid cancer. It has a more established role in monitoring progress of treatment, or in detecting a possible relapse.

Calcitonin

Calcitonin levels are particularly important in the diagnosis and monitoring of medullary thyroid cancer. These levels are usually high in cases of this type of cancer, although in some people with the inherited multiple endocrine neoplasia syndromes, they are not.

If you have medullary thyroid cancer, it is usually recommended you also have tests for levels of hormones released by the adrenal and parathyoid glands, as these are sites of associated cancers.

Scans

Ultrasound

An ultrasound uses soundwaves to create an image of the thyroid and nearby structures. An ultrasound can also be used to guide fine-needle aspiration (see 'Procedures' below).

Computerised tomography scan

A computerised tomography (CT) may be performed to determine the spread of cancer within the neck or to distant sites.

Procedures

Fine-needle aspiration

Fine-needle aspiration involves removal of thyroid tissue samples using a thin needle. Several samples will be taken from different parts of the thyroid. The tissue is sent to the pathologist for microscopic examination, to identify the type of thyroid cancer.

Laryngoscopy

Laryngoscopy uses a device called a laryngoscope to check your voice box (larynx). Specifically, the movement of your vocal cords is assessed. 

Computerised tomography

A scan that uses X-rays to create a 3D image of the body. This can detect abnormalities more effectively than a simple X-ray can.

Lymph nodes

A small organ of the lymphatic system containing many immune cells. Lymph nodes, also known as lymph glands, are the sites where many interactions between immune cells and foreign materials occur.

Metabolism

The sum of all chemical changes that take place within an organism to maintain growth and development and convert food into energy and building blocks.

Types of treatment

Surgery

Surgery is the main form of treatment for follicular, papillary and medullary thyroid cancers (the three most common types of thyroid cancer). Surgery can involve removing the entire thyroid gland (total thyroidectomy), most of the thyroid gland (subtotal thyroidectomy) or half of the thyroid gland (hemithyroidectomy).

In most cases of follicular and papillary thyroid cancers, the surgery removes the entire thyroid. This is also dependent of the size of the tumour. Lymph nodes near the thyroid are also often removed.

With medullary thyroid cancer, it is generally recommended that the entire thyroid gland is removed and that an examination of the lymph nodes around the thyroid is performed. 

It is not often that anaplastic thyroid cancer is caught at an early stage, but if it is thought to be restricted to the thyroid, then removal of the entire thyroid and often the surrounding tissues, is recommended.

Additional treatments

Radioiodine

Iodine is uniquely taken up by the thyroid gland's follicular cells, so it is concentrated within this organ. Using a radioactive form of iodine (radioiodine) enables destruction of the cells in the thyroid tissue. This includes both cancerous and non-cancerous cells.

Radioiodine is only used for papillary and follicular thyroid cancers, as these are the types that originate in the follicular cells. If you have radioiodine treatment, you will need to avoid activities such as sleeping in the same bed with someone and sharing of toothbrushes, shavers or utensils. This is to minimise the risk of exposing the people around you to radiation.

Radiotherapy

In this type of therapy, focused X-rays from an external beam radiation source are applied to the area where the tumour is located. Another form of radiation therapy is brachytherapy. This involves implanting radioactive seeds in the tumour or the nearby area, which deliver cell-destroying radiation directly into the tumour. Radiotherapy can be used alone, or in addition to surgery and/or chemotherapy.   

Thyroid hormone suppression

Thyroid hormone replacement therapy is needed for many patients after treatment for thyroid cancer, as most treatments affect normal tissue as well as cancerous tissues. Thyroid hormone is sometimes given in doses that suppress any normal production of thyroid hormone, to prevent the body stimulating remaining cancer cells. This treatment has not been definitively proven to improve outcomes, but its use is still common in all types of thyroid cancer, except anaplastic thyroid cancer.

Chemotherapy

Chemotherapy works by attacking cells, including cancerous cells, and stopping their reproduction. Various medications are used, which can be administered intravenously or orally. Chemotherapy is used in all types of thyroid cancer.

For patients with papillary or follicular thyroid cancer, it is generally reserved for patients for whom the cancer has persisted, despite using all other treatments.

In cases of anaplastic thyroid cancer, chemotherapy is often used as a stand-alone treatment, or in addition to radiotherapy and surgery. Unfortunately, since anaplastic cancer is often incurable, chemotherapy is used to only control the disease and improve qualitity of life.

Targeted therapy

Targeted therapies, such as tyrosine kinase inhibitors, are medications that block processes and pathways that are important for cancer cell growth and proliferation. In medullary thyroid cancer, these medications have not been shown to prolong survival but they do improve the quality of life. Studies are yet to reveal the impact of such medications on treatment of follicular and papillary thyroid cancer.

Other treatments

Some people diagnosed with cancer seek out complementary and alternative therapies. None of these alternative therapies are proven to cure cancer, but some can help people feel better when used together with conventional medical treatment. It is important to discuss any treatments with your doctor before starting them.

Iodine

A chemical element important for hormone development that is found in foods including dairy products, seafood, eggs, bread and some vegetables. It is often used in medicine as a dye.

Lymph nodes

A small organ of the lymphatic system containing many immune cells. Lymph nodes, also known as lymph glands, are the sites where many interactions between immune cells and foreign materials occur.

Radiation

Energy that is emitted, such as heat, light, or energy in electromagnetic waves. Different types of radiation can be used to diagnose and treat disease.

X-rays

A scan that uses ionising radiation beams to create an image of the body’s internal structures.

Potential complications

Treatment side effects

Side effects that can result from treatments for thyroid cancer include:

  • Surgery and radiotherapy can cause hypothyroidism, which is the reduced production of hormones by the thyroid. This can be supplemented with thyroid medication;
  • Injury to the voice box (larynx) or the nerves that supply the vocal cords can be caused by surgery, which can affect the tone of speech;
  • Low calcium levels can result from the accidental injury or removal of the parathyroid glands during surgery. This may need temporary or lifelong replacement with calcium supplements;
  • Salivary glands can be affected by radioiodine, causing a dry mouth or altered taste sensation;
  • Metastasis - this is when the cancer spreads to other parts of the body through the bloodstream and lymphatic system, affecting the vital function of organs, and;
  • Recurrence - thyroid cancer will return in up to a third of patients after initial treatment.

Lymphatic system

A network of vessels, lymph nodes, the spleen and other organs that transport lymph fluid between tissues and bloodstream.

Prognosis

Prognosis varies according to the type and stage of the cancer, but is generally very good. The overall five-year survival rate is 96%. For those who survive the first year, the survival rate increases to 98%. [1] These survival rates do not apply to the rare and aggressive form of thyroid cancer (anaplastic thyroid cancer) for which the average life expectancy, after diagnosis, is six months to a year.

It is important to remember survival rates are only an indication, and are based upon the averages of previously treated patients. It is not an absolute prognosis for an individual. It is often difficult to accurately predict an individual's cure or survival rate. Constant advances in treatment are continually improving these statistics. 

1. Cancer survival and prevalence in Australia: period estimates from 1982 to 2010. Australian Government – Australian Institute of Health and Welfare. Accessed 22 September 2014 from

External link

Prevention

Generally, development of a thyroid cancer cannot be prevented. However, in the case of familial medullary thyroid cancer, where gene mutations that increase the risk of developing the cancer have been identified, the thyroid gland may be removed as a preventative measure. 

Gene

A unit of inheritance (heredity) of a living organism. A segment of genetic material, typically DNA, that specifies the structure of a protein or related molecules. Genes are passed on to offspring so that traits are inherited, making you who you are and what you look like.

1. Cancer survival and prevalence in Australia: period estimates from 1982 to 2010. Australian Government – Australian Institute of Health and Welfare. Accessed 22 September 2014 from

External link