Demonstrating the undermining of science and health policy after the Fukushima nuclear accident by applying the Toolkit for detecting misused epidemiological methods

Abstract

It is well known that science can be misused to hinder the resolution (i.e., the elimination and/or control) of a health problem. To recognize distorted and misapplied epidemiological science, a 33-item "Toolkit for detecting misused epidemiological methods" (hereinafter, the Toolkit) was published in 2021. Applying the Toolkit, we critically evaluated a review paper entitled, "Lessons learned from Chernobyl and Fukushima on thyroid cancer screening and recommendations in the case of a future nuclear accident" in Environment International in 2021, published by the SHAMISEN (Nuclear Emergency Situations - Improvement of Medical and Health Surveillance) international expert consortium. The article highlighted the claim that overdiagnosis of childhood thyroid cancers greatly increased the number of cases detected in ultrasound thyroid screening following the 2011 Fukushima nuclear accident. However, the reasons cited in the SHAMISEN review paper for overdiagnosis in mass screening lacked important information about the high incidence of thyroid cancers after the accident. The SHAMISEN review paper ignored published studies of screening results in unexposed areas, and included an invalid comparison of screenings among children with screenings among adults. The review omitted the actual state of screening in Fukushima after the nuclear accident, in which only nodules > 5 mm in diameter were examined. The growth rate of thyroid cancers was not slow, as emphasized in the SHAMISEN review paper; evidence shows that cancers detected in second-round screening grew to more than 5 mm in diameter over a 2-year period. The SHAMISEN consortium used an unfounded overdiagnosis hypothesis and misguided evidence to refute that the excess incidence of thyroid cancer was attributable to the nuclear accident, despite the findings of ongoing ultrasound screening for thyroid cancer in Fukushima and around Chernobyl. By our evaluation, the SHAMISEN review paper includes 20 of the 33 items in the Toolkit that demonstrate the misuse of epidemiology. The International Agency for Research on Cancer meeting in 2017 and its publication cited in the SHAMISEN review paper includes 12 of the 33 items in the Toolkit. Finally, we recommend a few enhancements to the Toolkit to increase its utility.

Keywords: Cancer; Chernobyl; Overdiagnosis; Screening; Thyroid; Ultrasound.

Fig. 1

Epidemic curve of childhood cancer in Belarus from 1977 to 1994. Malko MV: Chernobyl radiation-induced thyroid cancers in Belarus. http://www.rri.kyoto-u.ac.jp/NSRG/reports/kr79/kr79pdf/Malko2.pdf.

Fig. 2

Directed acyclic graph explaining confounding owing to the timing of screening ^aScreening program was started according to the order of areas of Fukushima Prefecture with the highest contamination levels, determined using WHO Preliminary dose estimation [66] ☆ indicates the primary causal hypothesis in the present study ★ indicates main variables analyzed. Box indicates the adjusted confounding factor. Blue arrows indicate causal paths. The red arrow indicates the main causal path. The white arrow indicates the backdoor path induced by confounding. "+" or "-" with each arrow indicates positive and negative correlation, respectively

Fig. 3

Relationship between elapsed time since the accident and proportion of thyroid cancer detected via ultrasound echography among three screenings in three exposed areas

Fig. 4

Map of Fukushima Prefecture and its screening areas/districts for analysis