Thryoid Cancer

Causes

Thyroid cancer is among the more uncommon cancers; approximately 2,000 people develop it in the UK every year. It can affect anybody, of any age; however, certain subgroups of people can be affected more by a particular type.

In many cases, there is no clear cause of thyroid cancer. However, certain risk factors can increase the change of developing it.

    -Benign thyroid disease – certain people who have non-cancerous, benign thyroid diseases have a greater chance of developing cancer; approximately 20% of those with a disease will go on to develop thyroid cancer.

These diseases include: 

• Goitre (enlargement of the thyroid)
• Adenomas (thyroid nodules)
• Thyroiditis (inflammation of the thyroid)

As these disorders can run in families, you also have a slightly increased risk of developing cancer if a family member has one of these disorders.

Neither hyperthyroidism nor hypothyroidism has been shown to have an increased risk of cancer.

     -Radiation – a small number people who have been exposed to high levels of radiation, either as therapy (e.g. for other cancers) or in the environment (e.g. the nuclear explosion in Chernobyl, 1986) may go on to develop cancer as a result.

    -Genetics – research has linked particular cases of cancer to inherited mutations; these cancers tend to run in families. In particular, mutations in RET – a proto-oncogene – can lead to cancerous syndromes, including:

• Familial medullary thyroid cancer (FMTC)
• Multiple endocrine neoplasia (MEN) syndrome type 2A or 2B
• Familial adenomatous polyposis (FAP)

While this mutation does not automatically mean you will develop cancer, it is sometimes recommended that someone with this  abnormal gene, have their thyroid removed (a prophylactic thyroidectomy) to prevent cancer from developing.

Symptoms

Often thyroid cancer will progress without any symptoms. Many never present with symptoms and people live with the cancer for years, unaware they have it, as it does not affect their health.

When seen, symptoms include:

• Cough
• Difficulty swallowing or breathing
• Enlargement of the thyroid
• Hoarseness or a change in the voice
• Swelling of the neck
• Thyroid lumps (or nodules)

 In rare cases, thyroid cancer may first only been seen with secondary tumours on the lungs or bones. 

 Types

There Are four types of thyroid cancer:
-Papillary – this is the most common type of thyroid cancer (75-85% of cases) and holds the best prognosis; most patients survive and live long, healthy lives. It often occurs in women of child-bearing age, and is also seen in children.

-Follicular – this type is more uncommon (10-20% of cases) and, although it can metastasize, prognosis is usually very good. It is seen more in older women.

-Medullary – this type is quite rare (5-8%) and generally is familial; it is linked especially to mutations in the RET gene. It can be cured – however, prognosis is less good if the tumour cells metastasize.

-Anaplastic – although rare (less than 5% of cases), this type is often fatal; the cancer cells often metastasize and are unresponsive to even aggressive treatments.

Papillary and follicular cancers are both differentiated thyroid cancers; they are very similar and are usually treated in the same way.

Also seen in the thyroid are non-Hodgkin lymphomas – cancers of the lymph system. 

Diagnosis

A number of tests are used, often in combination, to diagnose thyroid cancer.

Blood tests – these involve removing a sample of blood from a vein and analysing it for levels of different substances. For thyroid cancer, tests examine levels of the following:

• Thyroid hormones T3, T4 and TSHs
• Elevated serum thyroglobulin (papillary or follicular) or calcitonin (medullary)
• Carcinoembryonic antigen (CEA)

Scans – various scans can be done to ascertain the location and nature of any lumps found in the thyroid. Ultrasound is the most common, but CT, MRI and PET scans are also used. Scintigraphy uses radioisotopes, taken internally, to form images: emitted radiation is detected using a gamma camera and used to form an image.

Fine-needle aspiration – this test uses a fine needle to remove a sample of tumour cells under anaesthetic. These cells are then analysed for certain markers or other indications of being cancerous.

Biopsy – if fine-needle aspiration fails to draw conclusive results, then a small piece of the thyroid can be surgically removed for further analysis.

Treatment

There are many different treatment options available to thyroid cancer patients; the particular choices or combinations of therapy ultimately depend upon the type of cancer it is, and how far it has progressed.

Surgery – this is the most common approach, Typically, patients undergo a partial or full thyroidectomy to remove tissue from or the entire thyroid. A lobectomy is performed if the cancer has spread to the lymph nodes; tracheotomy can be done if the cancer is large enough to compress the trachea.

Radioactive iodine – in combination with surgery, iodine-131 is often given to destroy residual cancerous cells from inside the body. As iodine is not absorbed in high levels by any other cells, only thyroid cells are affected. This treatment does not usually affect medullary or anaplastic tumours.

Radiotherapy – this can be applied with radioactive iodine, and is used if the cancer is inoperable, unresponsive to other treatments, or recurs later. High levels of ionising radiation are directed at the thyroid in an attempt to kill any remaining cells.

Chemotherapy – if tumours have spread, or are unresponsive to iodine-131, chemotherapy – strong anti-cancer drugs – can be used; however, this form of treatment is unusual, and often unnecessary, in many forms of thyroid cancer.

Patients who have their thyroid removed as part of cancer treatment will need to take replacement thyroid hormones for the rest of their lives.

Prognosis

The prognosis for thyroid cancer is among the best of all cancers. This is in part due to over-diagnosis bias – many cancers that are found do not produce symptoms or have any effect on the patient’s health. There are many recorded cases of patients living with thyroid cancer for many years and being completely unaware.

The exact prognosis differs between the types of cancer, and the stage at which it is diagnosed.

Anaplastic thyroid cancer is always considered to be stage IV; therefore, no data is available.

References

Adapted from https://www.cancer.org/cancer/thyroidcancer/detailedguide/thyroid-cancer-survival-rates

* F. Grünwald; Biersack, H. J.; Grںunwald, F. (2005). Thyroid cancer. Berlin: Springer. ISBN 3-540-22309-6.