Thyroid Cancer Risk Factors

Clinical studies of thyroid nodules and patients with thyroid cancer has identified specific risk factors which increase the probability that a nodule is malignant. This article review risk factors associated with a higher risk for cancer.

The vast majority of thyroid nodules are benign (approximately 95%). However, certain risk factors may increase the likelihood that a given nodule is malignant.

Age

Nodules that appear in children are two times as likely to be malignant than nodules that develop in adults. The risk of malignancy is higher in individuals over the age of 60 or under the age of 30 years.

Gender

The risk of malignancy for a nodule is higher in men than women. However, the incidence of thyroid cancer is still three times more common in women than men.

Family History

A family history positive for thyroid cancer increases the likelihood of a nodule being malignant. This is particularly true of if the family history is present in first-degree relatives (parents, siblings).

Exposure to Radiation

Prior exposure to radiation, particularly in children, increases the risk of thyroid cancer. The most common form of ionizing radiation exposure comes from individuals that receive radiation therapy for other cancers (head and neck tumors, Hodgkin's disease, lung cancer, total body irradiation for bone marrow transplantation, etc.). In most cases attempts to shield the thyroid are made. Back in the 1940's and 1950's some children were treated with radiation for things such as acne, tonsillitis, and to treat fungal skin infections. Individuals at risk for industrial exposure to ionizing radiation (x-ray technicians, research lab workers, nuclear industry workers) usually wear badges that measure radiation exposure.

Individuals with prior exposure to neck irradiation have a higher incidence of both benign and malignant nodules. It is estimated that approximately 30% of nodules are malignant in persons with prior neck irradiation.

Soft Risk Factors

Nodules that grow rapidly may have a higher incidence of malignancy. Nodules that are discovered incidentally on other imaging studies may have a higher incidence of malignancy. Nodules found on PET scans for surveillance of other cancers have a higher incidence of malignancy. Nodules that appear on a nuclear medicine test called a sestamibi scan also have increase likelihood of being malignant.

Summary

It is critical to remember that most thyroid nodules are benign. Thyroid nodule patients with one or more risk factors for thyroid cancer, are still-statistically speaking-most likely to have a benign nodule. Thyroid nodules do require systematic evaluation by an experienced thyroidologist. If risk factors for thyroid cancer are present, closer surveillance is warranted.

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