Is radioiodine treatment for thyroid cancer a risk factor for second primary malignancies

Radioiodine is a safe and well-established therapeutic modality for the ablation of thyroid remnants and the treatment of locoregional and distant metastases from differentiated thyroid carcinoma. However, a careful hazard assessment is mandatory in order to establish the risk–benefit ratio, especially in low-risk patients. Induction of second primary malignancies is one of the most serious possible untoward effects of radioiodine treatment. The limited incidence both of this effect and of thyroid cancer and the paucity of available dosimetric data make it difficult to perform high-quality studies that could provide evidence-based indications. A number of bias and confounding factors can blur data and must be considered, evaluating studies, addressing this topic. Data from the main surveys confirm that radioiodine can induce second primary tumors, with a probability comparable to that of external radiotherapy and lower than that of chemotherapy. Even though radioiodine treatment of thyroid cancer carries a low relative risk, the process of therapy justification must be carefully conducted and every measure that can reduce patient exposure must be taken, especially in children, adolescents and young adults.