Elevated Thyroid Cancer Incidence Seen in Children Near Fukushima Nuclear Plant

A new study has found an excess of thyroid cancer cases among children and adolescents who live near the Fukushima Daiichi nuclear power plant. The plant released radioactive material after the massive earthquake and tsunami crippled it in March 2011.

The World Health Organization previously predicted that thyroid cancer cases would spike following the incident at Fukushima. The Fukushima Prefectural Government conducted a screening program for thyroid cancer in all residents aged 18 years and younger beginning soon after the release of radioactive material in 2011; a second round of screening began in April 2014.

The first round of screening included 298,577 children and adolescents; screening numbers decreased year by year. The results were published online ahead of print in Epidemiology.

Among 2,251 ultrasound screen-positive cases by the end of 2014, 2,067 were examined further and 110 thyroid cancer cases were detected; 86 of those were histologically confirmed, and 1 case was diagnosed as a benign tumor.

They researchers, led by Toshihide Tsuda, PhD, of Okayama University in Japan, divided the screening population based on location. The highest incidence rate ratio (IRR) for thyroid cancer, as compared to the Japanese annual incidence, was 50, in the central middle district of the prefecture; that area was not evacuated following the earthquake and tsunami.

The analysis showed an excess risk in all areas studied, with one exception within the “least contaminated area” where no cases were found. The “nearest area” to Fukushima had an IRR of 30. Within that area, there was a prevalence of thyroid cancer of 359 per million individuals; in the central middle district where the IRR was highest, the prevalence was 605 cases per million individuals.

The investigators noted that the approximately 30-fold overall increase in thyroid cancer incidence might be the result of a screening effect, meaning there could be silent thyroid cancer cases among children in the unscreened parts of Japan. They conclude, however, that the magnitude of the IRRs is too large to be explained by such an effect.

They also compared this to the closest analog event in the history of nuclear power. “In Chernobyl, excesses of thyroid cancer became more remarkable 4 or 5 years after the accident in Belarus and Ukraine, so the observed excess alerts us to prepare for more potential cases within a few years,” the authors wrote.