Thyroid Cancer in Ukraine After the Chernobyl Accident: Incidence, Pathology, Treatment, and Molecular Biology

The number of thyroid cancer cases in those who were children and adolescents at the time of the Chernobyl accident is steadily increasing in Ukraine, and 466 newly diagnosed cases were observed in 2006. An estimation of the Clinical-Morphological Register data by age at the time of the accident shows that, for the post-Chernobyl period (1986-2006), 4369 cases of thyroid cancer have been registered in this age group, among which 3170 (72.6%) were children aged 0 to 14 years and 1199 (27.4%) were adolescents aged 15 to 18 years at the time of the accident. As well as in previous years, also in 2005-2006 the highest thyroid cancer incidence was registered in the six most contaminated northern regions of Ukraine. In the cohort of those born in 1968-1986 and operated on in 2005-2006, thyroid cancer was observed only in young adults 19-38 years of age, and more than 90% of these cancers were represented by papillary carcinoma. These tumours were mainly of papillary or papillary-follicular structure and presented with low levels of regional and/or distant metastases. Thyroid cancer incidence among children and adolescents born after the accident was much lower than in appropriate control patients born before the accident. Nevertheless, the pathological features of papillary carcinomas in both groups were similar. Molecular-biological studies showed that RET/PTC1, RET/PTC3 rearrangements and BRAF(V600E) mutations were detected only in papillary thyroid carcinomas. Unknown RET/PTC rearrangements (RET/PTCX) were observed in both malignant (papillary carcinomas) and benign (follicular adenomas) thyroid tumours. Papillary carcinomas with RET/PTC rearrangements were characterized by more prominent aggressiveness with respect to tumours with BRAF mutation or without any genetic alterations.