Differentiated thyroid carcinoma after 131I-MIBG treatment for neuroblastoma during childhood: description of the first two cases.

Background: It is well known that the thyroid gland is sensitive to the damaging effects of irradiation (X-radiation or I-131(-)). For this reason, during exposure to I-131-metaiodobenzylguanidine (MIBG) in children with neuroblastoma (NBL), the thyroid gland is protected against radiation damage by the administration of either potassium iodide (KI) or a combination of KI, thyroxine, and methimazole. Although hypothyroidism and benign thyroid nodules are frequently encountered during follow-up of these children, differentiated thyroid carcinoma (DTC) has never been reported after treatment with I-131-MIBG in children who have not been given external beam irradiation. Here, we describe the first two cases of DTC after I-131-MIBG-therapy. Patient Findings: A 6-year-old boy, treated with I-131-MIBG for NBL at the age of 4 months, and a 13-year-old girl, treated at the age of 9 months, were both diagnosed with DTC at 5 and 12 years after I-131-MIBG treatment, respectively. Both children received thyroid protection during exposure to I-131-MIBG. In each child DTC was discovered in nonpalpable nodules by thyroid ultrasound. Summary: The first two pediatric patients with DTC after treatment with I-131-MIBG are reported. Conclusions: Both these cases of DTC after I-131-MIBG for childhood NBL underline the importance of adequate thyroid protection against radiation exposure during treatment for NBL. Children who have been treated with I-131-MIBG should be given life-long follow-up, not only with regard to thyroid function, but also with surveillance for the development of thyroid nodules and thyroid cancer.