Systematic screening after Chernobyl: Insights on radiation‐induced thyroid cancer

Abstract

Radiation-induced thyroid cancer is 1 of the lingering public health effects of the Chernobyl Nuclear Power Station accident that occurred in 1986. Studies to date have underscored the increased risk of thyroid malignancies, in particular to children and adolescents who experienced environmental exposure to radioiodines. The risk appears to be age-related and dose-related, and it is probably modified by iodine deficiency, but most studies have relied on case-control or epidemiologic design. In this issue of Cancer, Zablotska and colleagues report on the incidence and characteristics of radiationinduced thyroid cancer that were detected after a systematic screening program was initiated for at-risk children and adolescents in Belarus. 1 The well considered, organized, and efficient screening strategy that was implemented by Zablotska et al is to be especially commended. The study was inclusive of 11,664 children and adolescents (aged <18 years) who lived in Belarus, had thyroid radioactivity measurements within 2 months after the Chernobyl accident, and were then screened during 3 separate periods (1997-2000, 2002-2004, and 2004-2006). Thyroid palpation and sonographic assessment occurred locally, and any patients who had dominant nodules or nodules with suspicious sonographic features were referred to study centers for fine-needle aspiration (FNA) biopsy. Patients underwent thyroidectomy for results in the follicular neoplasm, suspicious for malignancy, or positive for malignancy cytology categories. Yet another strength of the study design is the blinded review of pathologic specimens by a centralized group of pathologists who were unaware of the dose of radioiodine exposure. Compliance rates for FNA biopsy and surgery were a laudable 94.8% and 78.4%, respectively. The systematic screening, which followed current guidelines for invasive intervention, had an excellent compliance rate, and included a comprehensive pathology review for such a large population-based study, is truly admirable and provides highquality and interesting new data. Widespread adaptation of such an organized and evidence-based approach with centralization of expertise to guide nodule management should be the gold standard for thyroid research worldwide.And what does the data analysis indicate? It has been demonstrated previously that the risk of thyroid cancer depends on the dose of radiation exposure to the thyroid. 2,3 However, in contrast to several other studies, Zablotska et al also have clearly demonstrated a dose-dependent effect on histologic features of tumor aggressiveness, including lymphatic invasion, intrathyroid infiltration, and multifocality. The impact of iodine deficiency and subclinical thyroid disease could not be determined, and it is still possible that these and other environmental factors may attenuate or augment the risk of radiation exposure on the thyroid.The initially described histologic features of radiation-associated thyroid cancers after the Chernobyl accident were higher rates of extrathyroid extension and...