Radioactive iodine (RAI) treatment for hyperthyroidism is associated with long-term risk of death from solid cancers, particularly breast cancer, according to the results of a study published in JAMA Internal Medicine.
Researchers identified the findings from a long-term follow-up study of 18,805 patients with hyperthyroidism who were treated with radiation between 1946 and 1964. With RAI treatment, the thyroid absorbs most of the radiation, but other organs like the breast and stomach are also exposed during treatment.
Using a novel, comprehensive method of estimating radiation doses to each organ or tissue, researchers found a positive dose-response relationship between the dose absorbed by an organ and mortality from cancer at that site. It was statistically significant for female breast cancer, for which every 100 mGy increased relative risk of breast cancer mortality by 12%, and for all other solid tumors together, for which relative risk of mortality increased 5% per every 100 mGy. According to the researchers, this correlates to an estimated lifetime excess of 19–32 solid cancer deaths per 1,000 patients.
An estimated 1.2% of people in the United States has hyperthyroidism, and RAI is one of the most common treatments. The researchers said that their findings will help patients and providers discuss the risks and benefits of treatment. They also noted that additional studies of other treatment options, including newer drugs not available to the original cohort, are needed to accurately compare treatment options.