Hyperthyroidism I-131 Treatment
Cancer mortality risks following treatment for adult hyperthyroidism The most commonly used treatment for hyperthyroidism in adult patients in the U.S. is high-dose iodine-131. In a retrospective cohort mortality study of 35,593 hyperthyroid patients (79% female, 91% diagnosed with Graves disease, and 65% treated with I-131) treated between 1946 and 1964 in 26 clinics, approximately 50% of the cohort had died by the end of follow-up in December 1990. Although the total number of cancer deaths was close to that expected, there were small mortality excesses from cancers of the lung, breast, kidney, and thyroid, and a deficit of deaths from cancers of the uterus and the prostate gland. A 16% significant increase in mortality was observed among patients with toxic nodular goiter, and a 31% significant increase was seen among patients treated exclusively with antithyroid drugs. Radioactive iodine was not linked to total cancer deaths or to any specific cancer with the exception of a 4-fold excess of thyroid cancer. The conclusion was that neither hyperthyroidism nor I-131 treatment resulted in a significantly increased risk of total cancer mortality. Although thyroid cancer mortality was increased following I-131 treatment, in absolute terms the excess number of deaths was small, and the underlying thyroid disease appeared to play a role. Another followup of the cohort is currently underway to ascertain whether there are any late or long-term effects associated with I-131 treatment.