To the Editor:
Tsuda et al.1 evaluated the prevalence of thyroid cancer among children and adolescents after the Fukushima accident in zones of different level of radiation contamination. Based on the numbers in their Table 1, I calculated the means of thyroid cancer prevalence in three zones of radiation contamination (low, middle, high); the least contaminated area (Northeastern, Western, Southeastern, Iwaki City), the combined four districts with intermediate contamination (North middle, Central middle, Koriyama City, South middle), and the nearest area to the crippled reactor (Fig.). The error bars in the Figure indicate 95% confidence intervals. It is hard to see any association of thyroid cancer prevalence with radiation contamination. This makes it difficult to accept that radiation has caused an increase of thyroid cancer among children and adolescents in Fukushima Prefecture during 2011–2014. After Chernobyl, a sharp rise of thyroid cancers in children from Belarus was observed in 1990; during 1987–1991, the annual numbers of newly detected cancers were 4, 5, 6, 29, and 55, respectively.2 In Fukushima, therefore, an increase of thyroid cancers is likely not expected to occur before 2015.
1. Tsuda T, Tokinobu A, Yamamoto E, Suzuki E.. Thyroid cancer detection by ultrasound among residents ages 18 years and younger in Fukushima, Japan: 2011 to 2014. Epidemiology. 2016;27:316–322
2. Kazakov VS, Demidchik EP, Astakhova LN.. Thyroid cancer after Chernobyl. Nature. 1992;359:21