Childhood and Adolescent Thyroid Cancer in Fukushima after the Fukushima Daiichi Nuclear Power Plant Accident: 5 Years On

The accident at the Fukushima Daiichi Nuclear Power Plant occurred after the Great East Japan Earthquake on 11 March 2011, releasing a large amount of radioactive materials into the atmosphere. Questions were raised regarding the health effects of radiation exposure, which led to increased anxiety among the Fukushima residents about the possible development of thyroid cancer. Thus, thyroid ultrasound examinations began for those who were from the areas where the radiation doses were highest, and will continue for the long term. In total, 300 476 subjects aged 18 years or younger at the time of the disaster were screened from 9 October 2011 to 31 March 2014. The participation rate was 81.7% of the total population of this age and in the affected area. Among them, the proportions of those who fell into the categories A1 (no nodules or cysts present), A2 (nodule ≤ 5 mm or cyst ≤ 20 mm diameter), B (nodule > 5 mm or cyst > 20 mm diameter) and C (immediate need for further investigation) were 51.5, 47.8, 0.8 and 0%, respectively; 2294 subjects in categories B and C were recommended to undergo a confirmatory examination; 113 were subsequently diagnosed with malignancy or suspected malignancy by fine needle aspiration cytology. The full-scale survey (second round survey) began in April 2014, and was completed by 30 June 2015, and comprised 169 455 subjects (participation rate; 44.7%). The proportions of those who fell into the categories A1, A2, B and C were 41.6, 57.6, 0.8 and 0% (no case), respectively; 1223 subjects in category B were recommended to undergo a confirmatory examination, 25 of these were subsequently diagnosed with malignancy or suspected malignancy by fine needle aspiration cytology. The thyroid cancers identified in this survey so far are unlikely to be due to radiation exposure, and are more likely to be the result of screening using highly sophisticated ultrasound techniques. However, it would be advisable to continue long-term screening to determine whether the risk of childhood and adolescent thyroid cancer due to radiation exposure increases or not.