Fukushima Thyroid Examination February 2016: 51 Cases Suspicious or Confirmed of Thyroid Cancer in the Second Round Screening

116 Thyroid cancer cases confirmed in Fukushima as of December 2015--100 in the first round and 16 in the second round (Total of 166 cases with malignancy or suspicion of malignancy--115 in the first round and 51 in the second round).


The 22nd Prefectural Oversight Committee for Fukushima Health Management Survey convened in Fukushima City, Fukushima Prefecture, on Monday, February 15, 2016. 

(For the unofficial English translation of the most recent official information, only available in Japanese, on surgical and pathological details of some of the thyroid cancer cases, see this post).

Among other information, the Oversight Committee released the latest results (as of December 31, 2015) of the ongoing Full-Scale thyroid examination, or the second round screening, which is being conducted over a two-year period from April 2014 to March 2016. Although the so-called "final" results of Initial Screening, or the first round screening, were released at the last Oversight Committee meeting held on August 30, 2015, the secondary examination and surgical confirmation are still ongoing, and a few new additional results were orally presented. 

An official English translation of the results is available here. The narrative below contains some information gathered from the live webcast of the Oversight Committee meeting and the subsequent press conference.

Overview
As of December 31, 2015, there are 14 more (2 from the first round and 12 from the second round) cases with malignancy or suspicion of malignancy, for a total of 166 (167 including the single case of post-surgically confirmed benign nodule). The number of surgically confirmed cancer cases, excluding the aforementioned case of benign nodule, now totals 116 (100 from the first round and 16 from the second round), and the remaining 50 (15 from the first round and 35 from the second round) await surgical confirmation. Since the last results were released, only 1 additional case from the second round has been operated on and confirmed as papillary thyroid cancer by post-surgical pathological examination of the resected thyroid gland tissue.

Initial (Preliminary Baseline) Screening (a.k.a. the first round)
The first round targeted about 368,000 individuals who were age 18 or younger, residing in Fukushima Prefecture at the time of the Tokyo Electric Fukushima Daiichi nuclear power plant accident on March 11, 2011. There were 300,476 actual participants in the primary examination, giving rise to the participation rate of 81.7%. As of December 31, 2015, there are 116 cases with malignancy or suspicion of malignancy, including a case of the post-surgically diagnosed benign nodule: 101 underwent surgery and 100 were confirmed with thyroid cancer (97 papillary thyroid cancer and 3 poorly differentiated thyroid cancer). 

Full-Scale Screening (a.k.a. the second round)
To be conducted every 2 years until age 20 and every 5 years after age 20, the second round screening additionally targets those who were born in the first year after the accident, eventually aiming to examine approximately 385,000 individuals in a 2-year period. As of December 31, 2015, 236,595 have participated in the primary examination of the second round at the participation rate of 62.1% (target population as of December 31, 2015 is 381,261). 220,088 have received confirmed results of the primary examination, and 1,819 turned out to be eligible for the confirmatory examination. 

Of 1,172 who actually underwent the confirmatory examination, 1,087 received confirmed results including 157 that underwent fine-needle aspiration cytology (FNAC). 51 cases had FNAC results suspicious for cancer. Confirmation of thyroid cancer requires pathological examination of the resected thyroid tissue obtained during surgery. As of December 31, 2015, 16 underwent surgery and all 16 were confirmed to have papillary thyroid cancer.

An additional new data from the first round
Dr. Akira Ohtsuru, the head of thyroid ultrasound examination program, orally presented information from the still ongoing secondary examination of the first round, mentioning 2 new cases with malignancy or suspicion of malignancy since the last results. There was no additional surgically confirmed cases. No details such as age, gender, or municipality of residence, are known about the 2 additional new cases with malignancy or suspicion of malignancy from the first round. It is also not known how many cases were still pending results of the confirmatory examination. 

During the press conference, Asahi Shimbun jounalist Yuri Oiwa asked for age and gender of the two new cases from the first round. Otsuru declined to give the information, only stating that an addendum to the final report of the first round would be released at the next Oversight Committee meeting in May 2016.

Different age groups 
In the first round, results are based on age at the time of the accident in March 2011 unless specified to be the age at examination. Age groups in the first round are shown in increments of 3 to 6 years from age 0 to age 18: 0-5, 6-10, 11-15, and 16-18. Meanwhile, age groups in the second round results are based on age at the time of examination, unless specified otherwise (Table 3 showing participation rates by age groups is based on age as of April 1, 2014). Age groups in the second round are shown in increments of 5 to 6 years from age 2 to age 23: 2-7, 8-12, 13-17, and 18-23. 

Notably, the second round covers those who were born between April 2, 2011 and April 1, 2012: a cohort including those who were not conceived at the time of the accident and thus unexposed to the initial releases of radioactive iodine. Such cohort would yield valuable data of the unexposed population. This particular cohort also includes some who were already in utero, which also provides valuable data of in-utero exposure. Thus, the age 2-7 group in the second round includes both the in-utero exposed and the unexposed, but the breakdown of such data is not publicly available.

Incidentally, the reason for this time interval of April 2 to April 1 of the following year is the Japanese school year that starts in April: students born between April 2nd of the current school year and April 1st of the following year all enter the same grade. As thyroid ultrasound examination, like other school-based health checks and immunizations, has been taking place in school settings for school age children, officials decided to make sure students in the entire grade are "treated equally" so no children felt left out for having to or not having to go through the examination. (Conformity is considered a virtue in the Japanese society/culture, and any deviation can be a reason for bullying at any age, especially in children). 

Newly diagnosed cases in the second round
In the second round, 12 cases were newly diagnosed by FNAC to be malignant or suspicious of malignancy. There were 5 males (age at exposure: 8, 8, 15, 16 and 18) and 7 females (age at exposure: 7, 10, 11, 11, 12, 12, and 14). Their places of residence at exposure include 6 municipalities: FY 2014 target municipalities such as Minamisoma City, Motomiya City and Koriyama City (5 cases); and FY 2015 target municipalities such as Iwaki City, Sukagawa City, Soma City, Nakajima Village, and Aizuwakamatsu City. (In the first round, Minamisoma City was included in the FY 2011 target municipalities; Motomiya City and Koriyama City in the FY 2012 target municipalities; and Iwaki City, Sukagawa City, Soma City, Nakajima Village and Aizuwakamatsu City in the FY 2013 target municipalities). 

Prior diagnostic status of the cases newly diagnosed in the second round
Of 51 total cases with malignancy or suspicion of malignancy in the second round, 25 were A1, 22 were A2 (7 nodules and 15 cysts), and 4 were B in the first round. (In the 12 cases with malignancy or suspicion of malignancy reported this time, 6 were classified as A1, 4 as A2, and 2 as B in the first round). 

In general, cysts are considered benign by nature due to their cell type unless they contain solid components which could contain malignant cells. In the protocol of Fukushima thyroid ultrasound examination, cysts with solid components are placed in the nodule category in the size range of the cysts themselves. Nodules, on the other hand, could be benign or contain malignant or pre-malignant cells. 

25 cases that were A1 in the first round screened suspicious for malignancy in the second round. This would appear to be a new onset after the first round since A1 cases by definition have no ultrasound findings of cysts or nodules.

In 22 cases that were A2 in the first round, 7 were nodules and 15 were cysts. These 15 A2 cases with cysts, together with 25 cases that were A1 in the first round, represent 40 cases which developed thyroid cancer in 2 to 3 years since the first round. That is, unless these represented missed diagnoses.

According Ohtsuru, none of the cases had missed diagnoses in the first round. Otsuru did confirm during the press conference that there were no ultrasound findings for 25 cases that were A1 in the first round. However, he brought up a possibility that there might have been malignant cells already present at the time of the first round which could not be detected by ultrasound. (Medically speaking, this seems to be pure conjecture).

Ohtsuru also explained nodules would have to grow to be about 5 mm in diameter, or even 10 mm in some cases, to be detectible by ultrasound, although cysts could be detected beginning at 1 mm in diameter. However, this claim seems inconsistent with the long-standing claim by Fukushima Medical University that the ultrasound equipment being used is highly sensitive and capable of detecting very small lesions.

Ohtsuru seemed to be insinuating it was neither a missed diagnosis nor a new onset of cancer. 

Unfortunately, Dr. Kazuo Shimizu, a thyroid surgeon and one of the committee members, was absent this time, and no meaningful medical discussion ensued regarding these "newly appearing cancers." Dr. Shimizu previously stated that although it would be difficult to assess whether these cancerous tumors occurred pre- or post-accident, information such as the previous diagnostic category--nodules or cysts--of the new cases with malignancy or suspicion of malignancy might give some clue as to whether the cancer appeared after radiation exposure. 

Of 4 cases that were B in the first round, 2 were reported to have undergone FNAC in the first round, although the first FNAC results were undisclosed.



First Round or Initial Screening (October 2011 - April 2015)

Number of cases with malignancy or suspicion of malignancy: 116 (including one case of benign nodule)

Number with confirmed tissue diagnosis after surgery: 101

• 1 benign nodule
• 97 papillary thyroid cancer
• 3 poorly differentiated cancer

Second Round or Full-Scale Screening (April 2014 - March 2016)

Total number targeted: 381,261

Number of participants in primary examination: 236,595

Number with confirmed results: 220,088

• A1     89,565 (40.7%) (no nodules or cysts found)
• A2   128,704 (58.5%) (nodules ≦ 5.0 mm or cysts ≦ 20.0 mm)
• B        1,819   (0.8%) (nodules ≧ 5.1 mm or cysts ≧ 20.1 mm)
• C              0   (0.0%) (requiring immediate secondary examination)

(Note: Cysts with solid components are treated as nodules).

Number eligible for confirmatory (secondary) examination: 1,819

Number of participants in confirmatory examination: 1,172

Number with confirmed results: 1,087

Number of FNAB: 157

Number of cases with malignancy or suspicion of malignancy: 51

Number with confirmed tissue diagnosis after surgery: 16

• 16 papillary thyroid cancer

Unofficial translation of the selected tables from Full-Scale screening

Table 1. Primary examination coverage as of December 31, 2015


Table 2. Number and proportion of children with nodules/cysts as of December 31, 2015


Table 3. Participation rates in target municipalities for FY 2014 by age group as of December 31, 2015


Table 4. Changes in the results of Initial Screening and Full-Scale Thyroid Screening Program as of December 31, 2015

Note 1: Top line refers to the results of the Preliminary Baseline Screening for confirmed results of the Full-Scale Screening.
            It is not the breakdown of the total Preliminary Baseline Screening results, 300,476.
Note 2: Top line refers to the breakdown of the Full-Scale Screening results in a given category of the Preliminary Baseline Screening results. 
            Bottom line shows the proportion in %.

Table 5. Confirmatory testing coverage and results as of December 31, 2015


Table 6. Cytology results (including information from Appendix 6: Number of surgeries among cases with malignancy or suspicion of malignancy) as of December 31, 2015


Figure 3. Distribution of cases with malignancy or suspicion of malignancy by age (as of March 11, 2011) and sex (females in white and males in gray)


Figure 5.  Estimated external effective doses of those who submitted basic survey questionnaire as of December 31, 2015 (females in white and males in blue) 

Fukushima Thyroid Examination November 2015: 115 Thyroid Cancer Cases Confirmed--100 in First Round and 15 in Second Round Screening ( From 152 Malignant or Suspicious Cases--113 in First Round and 39 in Second Round)

The 21st Prefectural Oversight Committee for Fukushima Health Management Survey convened in Fukushima City, Fukushima Prefecture, on Monday, November 30, 2015. 

(For the unofficial English translation of the most recent official information, only available in Japanese, on surgical and pathological details of some of the thyroid cancer cases, see this post).

Among other information, the Oversight Committee released the latest results (as of September 30, 2015) of the ongoing Full-Scale thyroid examination, or the second round screening, which is being conducted over a two-year period from April 2014 to March 2016. Although the "final" results of Initial Screening, or the first round screening, were released at the last Oversight Committee meeting held on August 30, 2015, the secondary examination and surgical confirmation are still ongoing, and a few new additional results were orally presented. (Initial Screening is now officially called "Preliminary Baseline Screening," on the assumption that this post-exposure data reflect the baseline pediatric thyroid cancer occurrence in Fukushima Prefecture. Incidentally, Shunichi Yamashita et al. go so far as calling the first round screening results the "gold standard.")

An official English translation of the results will be available here. The narrative below contains some information gathered from the live webcast of the Oversight Committee meeting and the subsequent press conference.

In summary, as of September 30, 2015, there are 15 more (1 from the first round and 14 from the second round) malignant or suspicious cases, for a total of 152 (153 including the single case of post-surgically confirmed benign nodule). The number of surgically confirmed cancer cases, excluding the case of benign nodule, now totals 115 (100 from the first round and 15 from the second-round), and the remaining 37 (13 from the first round and 24 from the second round) await surgical confirmation. Since the last results were released, 11 cases (2 from the first round and 9 from the second round) have been operated on, and all 11 cases were shown to be papillary thyroid cancer by post-surgical pathological examination of the resected thyroid gland tissue.

Initial (Preliminary Baseline) Screening (the first round screening) targeted about 368,000 individuals who were age 18 or younger, residing in Fukushima Prefecture at the time of the Tokyo Electric Fukushima Daiichi nuclear power plant accident on March 11, 2011. There were 300,476 actual participants in the primary examination, giving rise to the participation rate of 81.7%. There are 114 malignant or suspicious cases, including the post-surgically diagnosed benign nodule: 101 underwent surgery and 100 were confirmed with thyroid cancer (97 papillary thyroid cancer and 3 poorly differentiated thyroid cancer). 

Full-Scale Screening (the second round screening), to be conducted every 2 years until age 20 and every 5 years after age 20, additionally targets those who were born in the first year after the accident, aiming to examine approximately 385,000 individuals in a 2-year period. As of September 30, 2015, about 200,000 have participated in the primary examination of the second round screening at the participation rate of 52.6%. 182,547 have received confirmed results of the primary examination, and 1,483 turned out to be eligible for the confirmatory examination. Of 1,023 who actually underwent the confirmatory examination, 879 received confirmed results including 124 that underwent fine-needle aspiration biopsy/cytology. Suspicion of thyroid cancer was found in 39. Confirmation of thyroid cancer requires pathological examination of the resected thyroid tissue obtained during surgery. As of September 30, 2015, 15 underwent surgery and all 15 were confirmed to have papillary thyroid cancer.

Dr. Akira Otsuru, the head of thyroid ultrasound examination program, orally presented information from the ongoing secondary examination of the first round, mentioning one new malignant or suspicious case and 2 surgically confirmed cases. No details are known about the single new malignant or suspicious case from the first round, such as age, gender, or municipality of residence. It is also not known how many cases were still pending results of the confirmatory examination. 

In the second round, 14 cases were newly diagnosed by fine-needle aspiration biopsy/cytology to be malignant or suspicious. There were 5 males (age at exposure: 7, 12, 15, 17 and 18) and 9 females (age at exposure: 8,10, 10, 12, 13, 15, 15, 16, and 16). Their places of residence at exposure include 6 municipalities: FY 2014 target municipalities such as Minamisoma City, Date City, Motomiya City, Koriyama City (9 cases), and Shirakawa City; and FY 2015 target municipality such as Iwaki City. (In the first round, Minamisoma City and Date City were included in the FY 2011 target municipalities, Motomiya City, Koriyama City and Shirakawa City in the FY 2012 target municipalities, and Iwaki City in the FY 2013 target municipalities). 

Of the 39 suspicious/malignant cases in the second round, 19 were A1 cases, 18 were A2 cases, and 2 were B cases in the first round. (Of the newly diagnosed 10 cases, 2 were A1 cases, 7 were A2 cases, and 1 was a B case in the first round). Dr. Kazuo Shimizu, a thyroid surgeon and one of the committee members, was concerned whether these 10 A1 and 13 A2 cases might have had lesions which were missed (i.e. missed diagnosis) in the first round. If they weren't missed diagnoses, that means either the first round lesions became cancerous or cancer newly appeared since the first round. Dr. Shimizu stated that although it would be difficult to assess whether these lesions occurred pre- or post-accident, this information might give some clue as to whether the lesion appeared after radiation exposure. 

In the previously A1 cases, cancer most likely appeared newly, as by definition A1 had no ultrasound findings. Dr. Otsuru did confirm there were no ultrasound findings for A1 cases. However, Dr. Otsuru also mentioned nodules would have to grow to be about 5 mm in diameter, or even 10 mm in some cases, to be detectible by ultrasound, although cysts could be detected beginning at 1 mm in diameter. In private conversation with other physicians, Dr. Otsuru was quoted to have said there might have been very small nodules present that were undetectable by ultrasound, insinuating it was neither missed diagnosis nor new lesion. However, this seems to be illogical as Fukushima Medical University claims the ultrasound equipment being used is highly sensitive and capable of detecting very small lesions.

The question is how many of the 18 A2 cases might have developed new lesions since the last screening: if the A2 diagnosis was for nodules, they could have been precancerous lesions, but cysts are usually not expected to turn cancerous unless there was a solid component within (however, cysts with solid components are considered nodules in the Fukushima thyroid examination protocol). According to Dr. Akira Otsuru, none of the cases had missed diagnoses in the first round, and 5 of the 18 A2 cases were nodules, with the remaining 13 being cysts. This means 32 cases (19 A1 cases and 15 A2 cases with cysts) had new suspicious/malignant lesions develop in the last 2-3 years since the first round screening.

As for the 2 cases which previously were diagnosed with B assessment, Dr. Otsuru said they had been followed in regular medical care, without fine-needle aspiration biopsy/cytology, after the first round examination, when it was time for them to undergo the second round examination.

Initial Screening (October 2011 - April 2015)
(confirmatory examination details were not provided)

Total number targeted: 367,685
Number of participants in primary examination: 300,476
Number with confirmed results: 300,476

• A1   154,606 (51.5%) (no nodules or cysts found)
• A2   143,576 (47.8%) (nodules ≦ 5.0 mm or cysts ≦ 20.0 mm)
• B        2,293   (0.8%) (nodules ≧ 5.1 mm or cysts ≧ 20.1 mm)
• C               1   (0.0%) (requiring immediate secondary examination)

(Note: Cysts with solid components are treated as nodules).

Number suspicious or confirmed of malignancy: 114 (including one case of benign nodules)

Number with confirmed tissue diagnosis after surgery: 101

• 1 benign nodule
• 97 papillary thyroid cancer
• 3 poorly differentiated cancer

Full-Scale Screening (April 2014 - March 2016)

Total number targeted: 379,952

Number of participants in primary examination: 199,772

Number with confirmed results: 182,547

• A1     74,985 (41.1%) (no nodules or cysts found)
• A2   106,079 (58.1%) (nodules ≦ 5.0 mm or cysts ≦ 20.0 mm)
• B        1,483   (0.8%) (nodules ≧ 5.1 mm or cysts ≧ 20.1 mm)
• C              0   (0.0%) (requiring immediate secondary examination)

(Note: Cysts with solid components are treated as nodules).

Number eligible for confirmatory (secondary) examination: 1,483

Number of participants in confirmatory examination: 1,023

Number with confirmed results: 879

Number of FNAB: 124

Number suspicious or confirmed of malignancy: 39

Number with confirmed tissue diagnosis after surgery: 15

• 15 papillary thyroid cancer

Unofficial translation of the selected tables from the Full-Scale Screening

Table 1. Primary examination coverage as of September 30, 2015

Table 2. Number and proportion of children with nodules/cysts as of September 30, 2015

Table 3. Participation rates in target municipalities for FY 2014 by age group (as of September 30, 2015)

Table 4. Changes in the results of Initial Screening and Full-Scale Thyroid Screening Program (as of September 30, 2015)

Note 1: Top line shows the number from the first round whose second round results have been confirmed. It is not based on the total number of the first round participants, 300,476.

Note 2: Top line shows the second round result detail of the applicable first round result.

Table 5. Confirmatory testing coverage and results as of September 30, 2015

Table 6. Cytology results (including information from Appendix 6: Number of surgeries among cases with malignancy or suspicion of malignancy) as of September 31, 2015

Figure 3. Distribution of suspicious/malignant cases by age (as of March 11, 2011) and sex (females in white and males in gray)

Figure 5.  Effective doses of those who submitted basic survey questionnaire (females in white and males in blue) as of September 30, 2015

Professor Toshihide Tsuda's Press Conference on "Pediatric Thyroid Cancer After the Fukushima Accident"

Below is the press conference presentation (in Japanese with English interpretation) given by Professor Toshihide Tsuda of Okayama University at the Foreign Correspondence Club of Japan (FCCJ) on October 8, 2015 (Japan time). 

On October 6, 2015, an epidemiological analysis of Fukushima thyroid cancer data by Professor Tsuda's research group was published online ahead of print in Epidemiology, official journal of the International Society for Environmental Epidemiology. The main author of the study, Professor Tsuda is an environmental epidemiologist who has devoted himself to clarifying the cause of health effects in numerous environmental cases such as Minamata disease, Nishi-Yodogawa air pollution in Osaka, and recognition of lung cancer in pneumoconiosis patients as an occupational disease. 


Here's the announcement of the press conference on the FCCJ website:

Thursday, October 08, 2015, 15:00 - 16:00

"Pediatric Thyroid Cancer after the Fukushima Accident" 

Toshihide Tsuda

Professor, Graduate School of 

Environmental and Life Science, Okayama University

Language: The speech and Q & A will be in Japanese with English interpretation

 Almost five years after the triple meltdown at the Fukushima Daiichi nuclear power plant, attention is turning to the possible long-term health effects radiation exposure has had on local people, particularly children.

 A large-scale thyroid ultrasound screening examination is underway in Fukushima Prefecture, covering about 370,000 children who were 18 or younger at the time of the accident.

 Despite evidence of much higher rates of juvenile thyroid cancer in the prefecture compared with the pre-accident incidence rate, local medical authorities and the central government claim that the Fukushima disaster is not the cause.

 They point to the evacuation of tens of thousands of people in the immediate aftermath, and the ban on the sale of locally produced milk and other produce. The authorities, 

backed by prominent international experts, claim the increased rate of thyroid cancer is due to the highly sensitive ultrasound equipment being used to test Fukushima children.

 But in a significant challenge to that thesis, Toshihide Tsuda, professor of environmental epidemiology at Okayama University, believes the excess occurrence of juvenile thyroid cancer is not due merely to the screening effect, but is the consequence of exposure to radiation.

 Tsuda, whose study appears in this month's Epidemiology, the journal of the International Society of Environmental Epidemiology, will come to the Club on 8 October to explain his findings and take questions.

 An expert in epidemiology and environmental medicine, Tsuda has devoted much of his career to the study of health and environmental pollution cases, including Minamata disease, air pollution in Nishi-Yodogawa, Osaka, and the recognition of lung cancer in pneumoconiosis patients as an occupational disease.

The official FCCJ video of the press conference is embedded below:

 


Below is the English version of the press conference presentation prepared ahead of time for distribution to participants. It is posted here with Professor Tsuda's permission.  Professor Tsuda did not necessarily adhere to these contents, however. Watching the video above is strongly encouraged as he explains his analysis in a clear manner, adding more background information and giving a mini lecture with power point presentation. English interpretation is of high quality, making the video highly informative. (In the video he talks about the Japanese government's lobbying effort to influence the draft version of the WHO dose estimation report. That information can be seen here).

 1. Overview of the paper    

Thyroid screening examination was started in all Fukushima residents age 18 or younger in October 2011 after the March 2011 Tokyo Electric Fukushima Daiichi nuclear power plant accident following the Great East Japan Earthquake and Tsunami. The first round screening (Initial Screening) conducted during FY 2011 through FY 2013 was completed, and the second round screening (Full-Scale Screening) is underway in FY 2014 and FY 2015. Ever since February 2013, the examination results have been released to the public, in Japanese as well as English, on the Fukushima Prefecture website. However, no epidemiological analysis has been carried out on the released data, leading to extremely insufficient conditions for causal inference, public health and clinical policy planning, future outlook and information disclosure to residents.
   The Okayama University team used standard epidemiological methods to analyze released data, and submitted the results as an original article to Epidemiology, official journal of the International Society of Environmental Epidemiology. I would like to report here that the article has been accepted and published online ahead-of-print.

【Original article】(PDF here)
Thyroid Cancer Detection by Ultrasound among Residents Aged 18 Years and Younger in Fukushima, Japan: 2011 to 2014
http://journals.lww.com/epidem/Abstract/publishahead/Thyroid_Cancer_Detection_by_Ultrasound_Among.99115.aspx

Toshihide Tsuda¹, Akiko Tokinobu², Eiji Yamamoto³, Tatsuji Suzuki2

1Department of Human Ecology, Graduate School of Environmental and Life Science, Okayama University; ²Department of Epidemiology, Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, Okayama University; ³Department of Information Science, Faculty of Informatics, Okayama University

Abstract

Background: After the Great East Japan Earthquake and Tsunami in March 2011, radioactive elements were released from the Fukushima Daiichi Nuclear Power Plant. Based on prior knowledge, concern emerged about a consequential increased incidence of thyroid cancer among exposed residents.

Methods: After the release, Fukushima Prefecture performed ultrasound thyroid screening on all residents aged ≤18 years. The first round of screening included 298,577 examinees (as of December 31, 2014), and a second round began in April 2014. We analyzed the prefecture results from the first and second round up to December 31, 2014, in comparison with the Japanese annual incidence and the incidence within Fukushima Prefecture.

Results: The highest incidence rate ratio, using a latent period of 4 years, was observed in the Central Middle District of the prefecture compared with the Japanese annual incidence (incidence rate ratio = 50; 95% confidence interval: 25, 90). The prevalence of thyroid cancer was 605 per million examinees (95% CI: 302, 1,082) and the prevalence odds ratio compared with the reference district in Fukushima Prefecture was 2.6 (95% CI: 0.99, 7.0). In the second screening round, even under the assumption that the rest of examinees were disease-free, an incidence rate ratio of 12 has already been observed (95% CI: 5.1, 23).

Conclusions: An excess of thyroid cancer has been detected by ultrasound among children and adolescents in Fukushima Prefecture within 4 years of the release, and is unlikely to be explained by a screening surge.


2. Significance of publication of the paper and the issue of screening effect and the overdiagnosis discourse　

   This analysis revealed that thyroid cancer incidence within three years of the accident increased by several tens of times in Fukushima residents who were age 18 or younger at the time of the accident in comparison to the Japanese annual incidence, and that it would be impossible to attribute the increase to reasons other than radiation, such as the screening effect or overdiagnosis. According to discussions by some specialists, screening effect refers to detection of so-called “true cancer” 2-3 years earlier than it would be diagnosed clinically. Overdiagnosis  refers to detection due to screening of so-called “false cancer,” or a mass of cancer cells, which may never be clinically diagnosed as cancer in life. In many of the ongoing discussions, these two — screening effect and overdiagnosis — are collectively called “screening effect,” with its meaning mainly referring to the definition of “overdiagnosis” stated above.
   Our analysis reveals that the thyroid cancer incidence at the end of 2014 far exceeds the 15-year thyroid cancer risk estimated in the WHO Health risk assessment from the nuclear accident after the 2011 Great East Japan earthquake and tsunami released in late February 2013. Moreover, while a tendency towards excess occurrence of thyroid cancer was beginning to be observed in Chernobyl in 1987 — the year after the accident, this analysis actually showed ultrasound screening allowed detection of an increased incidence of thyroid cancer within one year.
   I will now explain why the screening effect and overdiagnosis are not valid explanations for excess detection of thyroid cancer cases. First, the thyroid cancer incidence rate calculated in our analysis is 20-50 times the pre-accident rate. This is an order of magnitude higher than the increased incidence in thyroid cancer due to causes other than radiation exposure reported in the past. The effect generally called “screening effect” results in the incidence rate about several times higher than the pre-screening rate in cancers including thyroid cancer. It is impossible to explain the increased incidence this high by causes other than radiation.
   Next, despite repeated statements that there is no precedence of mass screening and follow-ups in populations with little exposure such as Initial Screening in Fukushima, studies have been published on the results of ultrasound screening in Chernobyl conducted in children and adolescents who were conceived and born post-accident or who lived in areas with relatively low levels of contamination. A total of 47,203 underwent screening, with not a single case of thyroid cancer detected. Although the age range slightly differs from screening in Fukushima Prefecture, this result cannot be explained by differences in the level of sophistication of ultrasound equipment in detecting 5 mm nodules.

*1: Demidchik YE et al. : Childhood thyroid cancer in Belarus, Russia and Ukraine after Chernobyl and at present. 
   Arq Bras Endocrinol Metab 2007; 51: 748-762.
*2: Shibata Y et al: 15 years after Chernobyl: new evidence of thyroid cancer. Lancet 2001; 358: 1956-1966.
*3: Ito M et al: Childhood thyroid diseases around Chernobyl evaluated by ultrasound examination and fine needle aspiration cytology. Thyroid 1995; 5(5): 365-368.

   Moreover, geographical variations in cancer detection rates (prevalence rates) within Fukushima Prefecture cannot be explained by the screening effect or overdiagnosis. Also, the emerging results of the second round screening point to the increased incidence rate which is already about 20 times higher than the pre-accident rate even under the assumption of large underestimation. When data released on August 31, 2015 are analyzed by areas and districts, it becomes apparent incidence rates in some areas and districts are beginning to exceed the first round incidence rates. As cases detected due to screening effect and overdiagnosis should have been harvested (harvesting effect), it is suggested the effect of radiation exposure due to the accident is beginning to appear within Fukushima Prefecture.
   In addition to overdiagnosis, a claim of overtreatment is often made. However, the post-surgical data of thyroid cancer cases operated at Fukushima Medical University, shows there is no evidence that premature or excessive surgeries were conducted, with the exception of 3 cases where patients and/or their families opted for voluntary surgery despite an option of non-surgical observational follow-up. Rather, the data suggests the fast progression of cancer in the operated cases. I am going to introduce an excerpt of the document titled, “Regarding Surgically Indicated Cases,” released by Professor Shinichi Suzuki of Fukushima Medical University.

Regarding Surgically Indicated Cases (see here for the complete translation of the original version)

“As of March 31, 2015, 104 among those eligible for thyroid examination underwent surgery after being diagnosed to have “malignant or suspicious” tumors in the confirmatory examination. 97 cases were operated on at the Division of Thyroid and Endocrine Surgery, Fukushima Medical University and 7 at other facilities. As 1 of 97 cases turned out to be a benign nodule post-operatively, 96 thyroid cancer cases are discussed here. According to the pathological evaluation, 93 cases were papillary thyroid cancer and 3 were poorly differentiated thyroid cancer. (…) The post-surgical pathological diagnosis revealed 28 cases (29%) with tumor diameter ≤ 10 mm, excluding 14 cases with mild extrathyroidal extension. And 8 cases (8%) had no lymph node metastasis, extrathyroidal extension, or distant metastasis (pT1a pN0 M0). Of all 96 cases, mild extrathyroidal extension (pEX1) was seen in 38 cases (39%), and lymph node metastasis was positive in 72 cases (74%). “  



3. Perspectives and reactions of international epidemiologists

   Starting with the WHO Health risk assessment, the majority of experts expected an increase in thyroid cancer incidence in Fukushima Prefecture after the accident. As a result, there was no strong opposition to the results of our analysis. We have analyzed newly released data and presented the results at the annual conferences of the International Society for Environmental Epidemiology (ISEE) in Basel in 2013, Seattle in 2014, and San Paulo in 2015. Our presentation drew a big interest, and the results of our analysis have been accepted without any issues other than astonishment about how high the rate is. This reaction made us feel that there is a large gap between the international expert opinions and the explanation of screening effect and overdiagnosis in Japan.


4. Recommendations as a public health specialist

   So far, hardly any radiation protection measures have been discussed other than evacuation in Fukushima Prefecture. Therefore, many recommendations can be presented given the results of our analysis. There is no reason not to prepare for the increased incidence at a full pace anticipated beyond 5 years after the accident or other expected situations. At present time, administrative bodies should urgently establish and implement countermeasures, including media relations, rather than discussing whether thyroid cancer cases have actually increased or not, or their causal relationship with radiation exposure.
   First, in preparation for the potential increase in thyroid cancer cases after the fourth post-accident year, medical resources should be checked to ensure that they are fully equipped. It appears that Fukushima Medical University owns a medical robotic system — the daVinci surgical system — which is supposed to eliminate visible scars of thyroid surgery. Its use should be considered even though it is not covered by the national health insurance.
   Next, an attempt should be made to keep track of thyroid cancer cases in an expansive  and well-developed manner, including cases in Fukushima residents 19 or older at the time of the accident or cases outside Fukushima Prefecture.
   Furthermore, the current assessment of thyroid cancer cases relies only on ultrasound screening. As time goes on, participation is likely to decline. A medical record booklet system such as the Hibakusha booklet should be established and the cancer registry should be well-developed in cooperation with prefectural and municipal medical associations.
   In addition, we need to prepare for and begin assessment and investigation of cancer other than thyroid cancer, such as leukemia, breast cancer and other solid cancers which are expected to increase according to the WHO Health Risk Assessment. Minimum latency period for blood-borne malignant neoplasms such as leukemia has already passed. Also, I believe it is necessary to investigate non-cancer illnesses and prepare to deal with them.
   Of course, it is necessary to gather further evidence to conduct a more detailed analysis of incidence data of thyroid cancer and other illnesses in Chernobyl. Also, dose estimation for radioactive iodine should be reconsidered due to an excess occurrence of thyroid cancer beyond the estimation by WHO.
   Naturally, the resettlement plan to return evacuees to areas with an air dose rate of 20 mSv/year should be postponed for the time being. If the resettlement plan is based on a scientifically incorrect statement, “Radiation-induced cancer does not occur, or is undetectable even if it occurs, under the exposure dose of 100 mSv,” then that’s all the more reason for the plan to be halted and reconsidered.
   As the air dose rate is still quite high, a more meticulous plan by age should be urgently prepared, although this has hardly been discussed in the past. In other words, further radiation protection measures should ideally be planned and implemented, including temporary evacuation plans for pregnant women, infants, toddlers, children, adolescents, and women with pregnancy potential, in that order.
   Lastly, I would like to discuss explanations consistently given in Fukushima Prefecture such as, “Cancer incidence will not increase due to the Fukushima nuclear accident” or “Even if cancer incidence increases, it will not be detectable.” These statements are only validated if both of the following two conditions hold true: 1) There is no (excess) occurrence of radiation-induced cancers below the exposure dose of 100 mSv; 2) Exposure dose in Fukushima Prefecture never exceeded 100 mSv, and all the exposure doses were much below 100 mSv. These two conditions have prevented most of discussions regarding realistic and cost-conscious radiation protection measures.
   But condition 1 is not even scientifically accurate, and no experts inside or outside Japan will make such a statement nowadays. And condition 2 is not accurate since the thyroid equivalent dose was estimated to exceed 100 mSv in residents outside the 20 km zone according to the WHO Preliminary dose estimation report released in 2012, which became the basis of the 2013 WHO Health risk assessment report. Our analysis showed results which appear to far exceed the 15-year thyroid cancer risk in the WHO Health risk assessment.
   However, it has only been four and a half years since the nuclear accident. Considering the average latency period for thyroid cancer and the time trend of excess occurrence of thyroid cancer in Chernobyl, it is highly likely that new thyroid cancer cases might appear every year at a 10 to 20 times higher rate than the last four and a half years. Under such a circumstance, a swift correction of statements by the government is needed: otherwise, trust will be lost, resulting in disruption to responses and measures to the reality. I hope our study will provide an opportunity to review announcements and response plans of the government. Current situations will only worsen anxiety, mistrust, and damages due to baseless rumors.