title: Quantification of the increase in thyroid cancer prevalence in Fukushima after the nuclear disaster in 2011--a potential overdiagnosis?
abstract: A thyroid ultrasound examination programme has been conducted in Fukushima Prefecture, Japan, after the nuclear disaster in 2011. Although remarkably high prevalence of thyroid cancer was observed, no relevant quantitative evaluation was conducted. We calculated the observed/expected (O/E) ratio of thyroid cancer prevalence for the residents aged ≤20 years. Observed prevalence was the number of thyroid cancer cases detected by the programme through the end of April 2015. Expected prevalence was calculated as cumulative incidence by a life-table method using the national estimates of thyroid cancer incidence rate in 2001-10 (prior to the disaster) and the population of Fukushima Prefecture. The underlying assumption was that there was neither nuclear accident nor screening intervention. The observed and estimated prevalence of thyroid cancer among residents aged ≤20 years was 160.1 and 5.2, respectively, giving an O/E ratio of 30.8 [95% confidence interval (CI): 26.2, 35.9]. When the recent increasing trend in thyroid cancer was considered, the overall O/E ratio was 22.2 (95% CI: 18.9, 25.9). The cumulative number of thyroid cancer deaths in Fukushima Prefecture, estimated with the same method (annual average in 2009-13), was 0.6 under age 40. Combined with the existing knowledge about radiation effect on thyroid cancer, our descriptive analysis suggests the possibility of overdiagnosis. Evaluation including individual-level analysis is required to further clarify the contribution of underlying factors.
authors.affiliation: Surveillance Division, Center for Cancer Control and Information Services, National Cancer Center, Tokyo kkatanod@ncc.go.jp.
authors.forename: Kota
authors.initials: K
authors.lastname: Katanoda
authors.affiliation: Center for Medical Education, Sapporo Medical University, Sapporo.
authors.forename: Ken-Ichi
authors.initials: K
authors.lastname: Kamo
authors.affiliation: Research Center for Cancer Prevention and Screening, National Cancer Center, Tokyo, Japan.
authors.forename: Shoichiro
authors.initials: S
authors.lastname: Tsugane
mesh_terms: D000328:Adult; D000368:Aged; D044466:Asian People / Q000706:statistics & numerical data*; D005260:Female; D062406:Fukushima Nuclear Accident; D006801:Humans; D015994:Incidence; D007564:Japan / Q000453:epidemiology; D015993:Life Tables; D008297:Male; D000069342:Medical Overuse / Q000706:statistics & numerical data*; D008875:Middle Aged; D015995:Prevalence; D011832:Radiation Injuries / Q000150:complications* / Q000209:etiology; D013964:Thyroid Neoplasms / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000453:epidemiology* / Q000209:etiology; D014463:Ultrasonography; D055815:Young Adult
keywords: early detection of cancer; radioactive hazard release; thyroid neoplasms; ultrasonography