Thyroid Cancer Risk Factors
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SECTIONS:
- Overview
- Thyroid Cancer Risk Factors
- Papillary Thyroid Cancer
- Follicular and Hurthle Cell Thyroid Cancer
- Medullary Thyroid Cancer
- Anaplastic Thyroid Cancer
- Thyroid Lymphoma
- Staging and Prognosis
Thyroid Cancer Risk Factors
Although the causes of thyroid cancer are not well understood, there are 2 main factors which are known to put an individual at higher risk of developing the disease:
- a family history of thyroid cancer and
- exposure to radiation.
Family History:
As with many types of cancer, a family history of thyroid cancer is a known risk factor. A family history of thyroid cancer carries the biggest risk for patients with first degree relatives (mother, father, sister, brother), second degree relatives (grandmother, grandfather, grandson, granddaughter), and/or multiple family members with thyroid cancer. About 5% of patients who develop papillary thyroid cancer and 20-25% of patients who develop medullary thyroid cancer have a relative who also had thyroid cancer. Medullary thyroid cancer (MTC) can be related to a disorder called Multiple Endocrine Neoplasia type 2 (MEN 2) Syndrome, and is usually the result of a specific genetic mutation in a part of the genome called the RET proto-oncogene. It is important that patients with MTC, as well as their families, be tested for this genetic abnormality (with a simple blood test) to see if they are risk for developing the disease.
See Medullary Thyroid Cancer »
Rarely, papillary thyroid cancer can also be genetically linked and may also be associated with familial forms of colon cancer, breast cancer, and goiters.
Radiation Exposure:
In the 1960's it was discovered that exposure of the head and neck areas to radiation during treatment of benign diseases increases the risk of developing thyroid cancer.
Since that time, this link has been found with exposure to significant doses of radiation from a variety of sources including:
Medical Exposure
In the first half of this century before antibiotics became available, radiation therapy was used to treat several benign diseases, such as acne, scalp ringworm, enlarged tonsils, enlarged thymus, enlarged lymph nodes in the neck as a result of tuberculosis, whooping cough, and keloid scars. In fact, over one million young Americans received x-ray treatments to the head or neck between 1920 and 1960. At the time, it was not known that the long term effects of this radiation therapy to the head and neck area would cause thyroid cancer (usually papillary thyroid cancer). When the association between radiation treatment and thyroid cancer was established, the use of this type of therapy was largely stopped. However, some of the most common radiation exposures today are during critical radiation therapy for different forms of cancer such as breast cancer, lymphoma, and lung cancer, among others. Of note, there have been NO long term, high-quality studies that have demonstrated a link between diagnostic X-rays done for testing purposes and thyroid cancer.
Environmental Exposure
In addition to radiation treatment, exposure to radiation as a result of nuclear weapons or nuclear plant accidents, such as that experienced by the survivors of Hiroshima, Nagasaki and Chernobyl, also increases the risk for developing thyroid cancer.
Fortunately, thyroid cancers usually have a very slow growth rate, which allows patients time to consider their treatment alternatives. In fact, thyroid cancer may not develop for 30 to 50 years after the radiation exposure. If a nodule is diagnosed as cancerous, complete cure can often be achieved. People who were exposed to radiation are also more likely to develop thyroid nodules in general and should have any suspicious nodules evaluated. There is some evidence that iodine may play a role in the prevention of aggressive thyroid cancer. It can also cut the risk of exposure to radiation from nuclear accidents if it is given in advance of the exposure.
