Below is a synopsis of the thyroid ultrasound examination, being conducted in Fukushima Prefecture since October 2011. The synopsis is intended to organize and clarify available information regarding thyroid cancer cases discovered in Fukushima residents, who were under age 18 at the time of the March 2011 Fukushima nuclear accident. It also includes some information gathered from various committee meetings, conducted and streamed live online only in Japanese.
Fukushima Thyroid Examination Fact Sheet: May/June 2014
In October 2011, seven months after the Fukushima Dai-ichi nuclear power plant meltdowns and explosions, Fukushima Prefecture began thyroid ultrasound examination, as part of Fukushima Health Management Survey1 (now called Fukushima Health Survey), in over 360,000 children. These children were younger than 18 at the time of the accident, and most of them did not receive adequate protection of stable iodine tablets for prevention of thyroid cancer. This was intended to be the baseline examination to assess the current condition of their thyroid glands. The thyroid gland is known to be affected, especially in children, by radioactive iodine 131 emitted from a nuclear accident.
The plan was to conduct the preliminary (first-round) thyroid ultrasound examination in all 360,000 plus children, beginning with municipalities with the highest radiation exposure doses. With Fukushima Medical University (FMU) being the sole conductor of the examination initially, as commissioned by Fukushima Prefecture, the first round of the examination was completed in late March 2014, at the end of Fiscal Year 2013. Cumulative results have been released every 2 to 4 months2, as the examination progressed on each year's cohort.
The final results of the first round of thyroid ultrasound examination from October 2011 to March 2014 are not yet known as of May 2014, since the secondary examination has not been completed. However, the results tallied up to March 31, 2014 were released on May 19, 2014, at the 15th Prefectural Oversight Committee Meeting for Fukushima Health Survey3.
Thyroid ultrasound examinations conducted on 295,511 Fukushima children (final results known for 287,056 children as of February 21, 2014) since October 2011, revealed that 136,804 children (47.7%) had an "A2" assessment, with either cysts 20.0 mm or smaller or nodules 5.0 mm or smaller. In addition, 2,069 children (0.7%) had a B assessment, indicating cysts 20.1 mm or larger or nodules 5.1 mm or larger, qualifying them for secondary examinations, including a more detailed ultrasound examination, blood and urine tests checking for thyroid function and iodine excretion, and fine-needle aspiration biopsy if necessary. Of these 2,069 children, 1,754 actually received the secondary examination.
So far, there are 49 papillary thyroid cancer cases, which were the most common form of thyroid cancer found in children after the 1986 Chernobyl accident, and 39 have suspect biopsies, meaning they need surgery to obtain a section of thyroid gland for tissue biopsy. Another cancer case is suspected to be of the poorly-differentiated subtype, with the final tissue diagnosis pending. The total number of confirmed thyroid cancer cases is 50, and the total number of confirmed and suspected cancer cases is 90 (this number is sometimes reported as 89, excluding one case that was confirmed to be benign). 32 were male and 58 were female, with an average age of 14.7 ± 2.7 (age range 6-18) at the time of the accident. The tumor size ranged from 5.1 mm to 40.5 mm. The youngest was a girl who was 6 at the time of the accident.
The incidence, or more accurately, prevalence, is thus 30.1 per 100,000 overall or 16.6 per 100,000 for confirmed cases so far. Although it is not possible at this time to determine if these cancers are radiation-induced or not, drawing on Japanese cancer incidence statistics, 3 or fewer cases of thyroid cancer would be expected in this population per year. (In 2010, normal incidence of thyroid cancer in Japan was 0.1 in 100,000 below age 15 and 1.1 in 100,000 in age 15-194,5). According to the National Cancer Institute, pediatric thyroid cancer incidence in the US, is 0.2 in 100,000 below age 15 and 1.76 per 100,000 in age 15-19 (12.2 in 100,000 in adults6).
So far, the official consensus of the Ministry of the Environment (MOE) of the Japanese government, FMU, and the United Nations Scientific Committee on the Effect of Atomic Radiation (UNSCEAR) appears to be that the finding constitutes a “screening effect,” which means thyroid cancer is being discovered as all children in Fukushima Prefecture are screened7,8. MOE also conducted a study in distant prefectures, supposedly unaffected by radiation exposure, but the study population is not age- and sex-matched to the Fukushima cohort and the two datasets cannot be directly compared9.
It should be noted that about 20% of the 368,651 Fukushima children never underwent the first round of thyroid ultrasound examination for various reasons. In addition, about 15% of the 2,070 children are yet to undergo the required secondary examination, and 10% of the 1,754 who underwent the secondary examination are still awaiting their results.
In the full-scale examination beginning April 2014, those born between April 2, 2011 and April 1, 2012 will be included, some of who were exposed in utero, making the total to be examined 385,000 in a two-year period. Fukushima Prefecture is now offering more facilities to conduct the examination in Fukushima. Agreements have been signed with various medical facilities nationwide to conduct the thyroid examination, so that 17,634 children residing outside Fukushima Prefecture can have an easier access.
Shunichi Yamashita, in charge of the Fukushima Health Survey until March 2013, initially claimed any thyroid cancer discovered during the screening would be latent cancers which would not have been discovered until much later if the screening hadn't been conducted.
At the June 2013 meeting of the Thyroid Examination Assessment Subcommittee, Shinichi Suzuki, an FMU professor currently directing the thyroid examination, admitted that some of the 50 cancer cases had lymph node metastasis or symptoms such as hoarseness which validated thyroidectomy. Suzuki had also maintained these cancers represented latent cancers.
This revelation came when Suzuki was grilled about the possibility of overdiagnosis and overtreatment by one of the subcommittee members, Kenji Shibuya10, a public health specialist at the University of Tokyo Graduate School of Medicine. Shibuya co-authored an article raising the issue of thyroid cancer overdiagnosis and overtreatment, published in Lancet11 in May 2014.
Although Suzuki mentioned the existence of conditions which would justify surgery, he would not release any detailed data such as the actual number of such cases. However, his admittance of lymph node metastasis in some of the cases seems to contradict the initial claim that these cancers were latent cancers which would never have been found.
This is a controversial topic, and we are awaiting a release of some of the data by FMU. By the way, although no longer attending the Prefectural Oversight Committee Meeting for Fukushima Health Survey, Shunichi Yamashita remains as the senior director of thyroid ultrasound examination12.
5 Matsuda A, Matsuda T, Shibata A, Katanoda K, Sobue T, Nishimoto H and The Japan Cancer Surveillance Research Group. Cancer Incidence and Incidence Rates in Japan in 2008: A Study of 25 Population-based Cancer Registries for the Monitoring of Cancer Incidence in Japan (MCIJ) Project. Japanese Journal of Clinical Oncology, 44(4): 388-396, 2013