A risk factor is something that increases your chance of developing cancer.

It is possible to develop thyroid cancer with or without the risk factors listed below. However, the more risk factors you have, the greater your likelihood of developing thyroid cancer. If you have a number of risk factors, ask your healthcare provider what you can do to reduce your risk.

Risk factors for thyroid cancer include the following:

Although thyroid cancer can occur at any age, the majority of people diagnosed with this condition are over the age of 40. Most people diagnosed with anaplastic thyroid cancer are over age 60.

Except for medullary cancer, women are about 3 times as likely as men to develop thyroid cancer.

Medullary thyroid cancer sometimes runs in families as part of a syndrome called multiple endocrine neoplasia. Families with a history of goiter development or colon polyps also have a tendency to develop papillary thyroid cancer. You are particularly at risk of developing endocrine cancers, such as medullary thyroid cancer, if you have a certain kind of genetic change (mutation) in something called the RET gene. People with acromegaly and Sjogren's syndrome also have an increased risk of thyroid cancer.

A history of exposure to radiation (especially during childhood) is a very strong risk factor for the development of thyroid cancer. Exposure may have occurred during medical treatments (for example, during radiation treatments for acne or enlarged tonsils, as was performed between the 1920s and the 1950s in the United States) or due to accidental exposure to radioactive fallout from nuclear power plant accidents, such as the one that occurred in Chernobyl, Russia. Up to 70% of papillary thyroid cancers have a mutation in the BRAF gene. It is thought to be related to exposure to radiation.

Iodine is necessary for thyroid hormone production. Without enough iodine, the thyroid enlarges to form a mass called a goiter. In the United States, iodine is commonly added to table salt, preventing most Americans from being deficient. In areas of the world where iodine deficiency occurs more frequently, there are higher rates of goiter, as well as thyroid cancer.

Your body chemistry changes when you gain weight. These changes may influence specific metabolic processes. Obesity is associated with an increased risk in thyroid cancer.

Incidence of thyroid cancer is highest in the Hawaiian and Polynesian islands and lowest in Poland.