Role of low-cost thyroid follow-up in children treated with radiotherapy for primary tumors at high risk of developing a second thyroid tumor

Aim. Differentiated thyroid cancer (DTC) is uncommon in childhood and data on its prevalence as a second malignant neoplasm (SNM) after radiotherapy (RT) for malignancies are limited. We evaluated: 1) the incidence DTC in pediatric-oncologic patients treated with RT; 2) the relationship between DTC, RT and the features of the first malignancy; 3) the usefulness of thyroid follow-up in irradiated oncological patients. Methods. We have followed up 252 patients treated with RT out of 966 oncologic pediatric patients. Thyroid follow-up included TSH level evaluation and neck ultrasonography. In the presence of thyroid nodule/s >= 1 cm and/or with ultrasonography suspicious for malignancy, fine needle aspiration biopsy (FNAB) was performed. When papillary/follicular lesions were detected by cytology, thyroidectomy was performed. If DTC was confirmed, patients underwent radioactive iodine (RAI) treatment. Results. At least one thyroid nodule was detected in 106 irradiated patients (42%): 45 patients underwent FNAB and 27 underwent thyroidectomy. Seventeen DTC (6.7%) were found on histology. A higher incidence of DTC was seen in patients with neuroblastoma (38%) or Wilms' tumor (18%). One third of DTC showed capsule invasion, and one fourth node involvement. Eleven patients, treated with a single RAI treatment, showed undetectable thyroglobulin levels after rh-TSH-stimulation. Five patients underwent at least two RAI treatments: four patients showed complete remission and one patient partial remission. Conclusion. A high rate of DTC, often with invasive features, was observed in children treated with RT for primary tumors. This finding underlines the usefulness of thorough low-cost thyroid follow-up in this high-risk population.