Etiology and Risk Factors
Radiation exposure to the thyroid gland in childhood, age, female sex, and family history are risk factors known to increase the incidence of well-differentiated thyroid cancer. Exposure of radiation to the thyroid may occur either from external sources or from ingestion of radioactive material.
Several studies have shown an inverse relationship between increased risk of thyroid cancer and age of exposure to radiation. Relative risk is also linearly related to exposure dose, starting as low as 0.1 Gy, and at least up to 30 Gy.10 The latency period after childhood exposure is at least 3 to 5 years, and there is no apparent drop off in the increased risk even 40 years after the radiation exposure.10 The majority of cases occur between 20 and 40 years after exposure. However, even after 40 years, the relative risk as compared to a nonirradiated population is still increased. For these reasons, the large cohort of patients who underwent childhood irradiation for benign medical conditions such as thymic enlargement and acne between 1920 and 1960 are now between the ages of 50 and 90 years of age have an increased risk of developing thyroid carcinoma.
Although the use of radiation for benign conditions has not been practiced since the 1960s, there is increased use of radiation treatments for neoplastic conditions, in infants, children, and young adults. The majority of this population have either Hodgkin’s or non-Hodgkin’s lymphoma but also includes long-term survivors ...
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