Acute Leukemia After Radioactive Iodine (I131) Therapy for Hyperthyroidism

During the 13 years since radioactive iodine, I¹³¹, became available, there has been little direct evidence to cast doubt on its safety. Attention has been focused largely on the possibility that radioactive iodine therapy for hyperthyroidism would lead to a higher incidence of cancer of the thyroid.^1,2 This concern is based on the obvious fact that thyroid tissue is by far the most heavily irradiated after radioactive iodine administration, by the observation that there is an increased incidence of carcinoma of the thyroid in children treated with x-ray therapy of the thymus,^3,4 and by animal experiments in which carcinoma of the thyroid was produced by irradiation.⁵ Recently, the occurrence of adenomata in three patients who had received radioactive iodine therapy for hyperthyroidism before the age of 20 has been reported.⁶ In one of these, the pathological findings were interpreted as "low-grade follicular carcinoma."

The possibility that radioactive iodine may be