Excerpt
On the basis of the linear no-threshold theory (LNT), the Chernobyl accident (CA) was predicted to result in a considerable increase in radiation-induced cancer among general public. In fact, there has been no cancer increase proven to be a consequence of the radiation exposure after CA except for thyroid carcinoma (TC) in people exposed at a young age. Appearance of radiogenic TCs after the accident is not denied here, but their number has been overestimated due to the following mechanisms. Prior to the accident, the registered incidence of pediatric TCs was lower in the former Soviet Union (SU) than in other developed countries apparently due to differences in diagnostic quality and coverage of the population by medical checkups. For example, in the northern provinces of Ukraine the incidence was 0.1, Belarus—0.3, Norway—1.4, Canada—1.6 per million per year [
1,
2]. Early cases of pediatric TC after the accident were generally described as poorly differentiated, aggressive, invasive and metastatic tumors [
3]. For example, three quarters of the tumors reported from contaminated areas of Belarus in 1992 were more than 1 cm in diameter; in 55 of the 131 cases there was a spread to the tissues surrounding the thyroid; six children had distant metastases [
4]. Furthermore, there was a pressure to be registered as Chernobyl victims to get access to benefits and health provisions. Biased information could be given e.g. that a child had been on contaminated territories at the time of the accident. There was no regular screening outside the contaminated areas, so that TC cases from outside must have been averagely more advanced. Accordingly, the “first wave” TC after the accident were averagely larger and less differentiated than those detected later [
5], when the pool of neglected cancers was gradually exhausted by the screening while reliability of the registration probably improved with time. According to Williams et al. [
6] aggressiveness and morphological features of Chernobyl childhood papillary TCs were not associated with radiation exposure. Along with the dose-dependent increase in TC risk, correlations between thyroid doses, tumor invasiveness and presence of the dedifferentiated solid-follicular histological pattern were reported [
7‐
9]. However, it can be reasonably assumed that cases with higher doses, residing in more contaminated and more intensely screened areas, were detected averagely earlier, when the pool of advanced TC was still untapped. Therefore, the following argumentation is unfounded: “The risk estimate was similar for microcarcinomas and for larger tumors, as well as for tumors with and without lymph node involvement, suggesting thyroid screening is unlikely to entirely account for the observation” [
7]. In fact, the screening detected not only small tumors but also large neglected ones, misclassified as aggressive radiogenic TCs. …
