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.