Hyperthyroid Follow-Up Study

Hyperthyroidism (thyrotoxicosis) is a relatively common disease, especially among women, and radioiodine (I-131) administration is the treatment of choice for most adult patients. There is concern about possible carcinogenic effects of I-131 therapy, but previous studies of hyperthyroid patients have not presented clear results regarding cancer risks following I-131 treatment. There also is public concern regarding late health consequences of I-131 exposure as this radioiodine is one of the primary release products from nuclear power generation and a principal component in fallout from nuclear power plant accidents. The Thyrotoxicosis Therapy Follow-up Study (TTFUS) cohort, assembled in 1961, comprises 35,000 subjects treated for hyperthyroidism at over 20 medical centers in the US and one in Great Britain between 1946 and 1964. This is among the largest group of hyperthyroid patients that has been followed up for subsequent cancer and other health outcomes. The proposed mortality follow-up study will enable us to assess nearly lifetime risk of cancer and other diseases in this unique cohort. Mortality follow-up data will extend the observation through 2015, adding 15 more years, via linkage with the National Death Index search. Recently estimated I-131 radiation doses to various body organs will allow refined dose response analysis, providing most definitive assessment of the nature and magnitude of the risk of cancer and other disease associated with I-131 exposure as well as end-results of I-131 and other treatment for hyperthyroidism.