Thyroid Cancer Causes and Risk Factors

Thyroid cancer is a cancer that occurs in the thyroid gland, a gland that located in the front of neck (below the larynx) that are responsible for producing hormones, which are important in the regulation of your metabolism, heart rate, blood pressure, and body temperature.

A normal thyroid gland has two lobes, the right lobe and the left lobe – joined by a narrow piece of gland called the isthmus. A healthy thyroid gland is barely palpable, which means it is hard to find by touch. If a tumor develops in the thyroid, it is felt as a lump in the neck.

Thyroid gland anatomy
Source: National Cancer Institute

Thyroid cancer usually begins as small lumps (nodules) in the thyroid gland. While some nodules may be cancerous, which means they can spread to other parts of the body, most thyroid nodules are benign (non-cancerous).

Thyroid cancer is the most rapidly increasing cancer in the US. The American Cancer Society estimates that 52,070 new cases of thyroid cancer will be diagnosed in 2019.

Types of Thyroid Cancer

There are four main types of thyroid cancer:

Differentiated thyroid cancers (DTC)

Most thyroid cancers are differentiated cancers, which look and behave similar to normal cells. These cancers usually develop from thyroid follicular cells. Over 90% of thyroid cancer patients have the differentiated form. DTCs are divided into two groups; papillary and follicular thyroid cancer.

  • Papillary thyroid cancer. This cancer develops in the follicular cells of the thyroid and it is by far the most common type of thyroid cancer. People with the papillary type tend to have more than one cancerous nodule in the thyroid gland.
  • Follicular thyroid cancer. Like papillary thyroid cancer, follicular cancer is also a DTC, but it is far less common than papillary thyroid cancer. If follicular thyroid cancer spreads, it is more likely to be found in the lungs or bones. Some patients have a mix of papillary-follicular thyroid cancer.

Medullary thyroid cancer (MTC)

Unlike DTCs which originate in the follicular cells of the thyroid, medullary thyroid cancer originates in the C cells of the thyroid, which produce calcitonin, a hormone that helps control the amount of calcium in blood. MTC accounts for only about 4% of all thyroid cancer cases.

Anaplastic thyroid cancer (ATC)

Anaplastic thyroid cancer, also called undifferentiated carcinoma, is a rare form of thyroid cancer, accounting for only 2% of all thyroid cancers. This cancer is called undifferentiated cancer because the cancer cells do not look and behave like normal thyroid cells. This cancer often spreads quickly and is much harder to treat.

Hurthle cell cancer (HCC)

Hurthle cell cancer is cancer that is arises from a certain type of follicular cell. About 4 out of every 100 cases of thyroid cancer are this type. Hurthle cell cancer is more likely to spread to lymph nodes than other follicular thyroid cancers. It is also most commonly found in people around the age of 50.

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The exact cause of most thyroid cancers is not yet known, but there are some factors that might increase your risk of developing it.

Age and gender

Thyroid cancer can occur at any age, but it is more common in women than in men. Women who are diagnosed with thyroid cancer are typically in their 40s or 50s and men are usually in their 60s or 70s.

Family history

The risk of developing thyroid cancer is higher if you have a close relative (parent, brother, sister or child) with thyroid cancer. But the risk is still very small because the cancer is quite rare.

Race

White Americans and Asian/Pacific Islander are more likely to develop thyroid cancer, but this disease can affect a person of any race or ethnicity.

Radiation exposure

Having head or neck radiation treatment is a risk factor for thyroid cancer and the risk increases with larger doses and with younger age at treatment. Sources of such radiation include radiation therapy and radiation fallout from power plant accidents or nuclear weapons.

Lack of iodine

Iodine is needed for normal thyroid function. A diet that is low in iodine has been associated with an increased risk of follicular thyroid cancers. This may explain why these cancers are seen less frequently in the United States, where iodine is added to salt and other foods

Genetic conditions

Certain genetic mutations such as RET, BRAF, and multiple endocrine neoplasia (MEN), are known to increase the risk of thyroid cancer. If you have a parent with this genetic mutation, you have a 50% chance of inheriting it.

Other inherited genetic conditions, such as familial adenomatous polyposis (FAP), Gardner syndrome, Cowden disease and Carney complex type-I, are considered risk factors for thyroid cancer, particularly papillary and follicular thyroid cancers.

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