⁂ Update on November 10, 2019: The final version submitted to the 35th meeting of the Oversight Committee on July 8, 2019 had an addition of "and prospective" in the second to the last sentence as shown below.
Further, in the future, estimated thyroid exposure doses should be used in case control and prospective studies with confounding factors adjusted, in order to evaluate an association between doses and thyroid cancer incidence rates.＊＊＊＊＊＊＊＊＊
On June 3, 2019, the 13th Thyroid Examination Evaluation Subcommittee (herein, the TUE Subcommittee) was held, marking the end of a two-year term for the members. As it is customary for committees to produce a report at the end of the term, a draft version of the "interim report" was submitted by Gen Suzuki, chair to the TUE Subcommittee, concluding, "at this time, no association is seen between thyroid cancer detected in the second round and radiation exposure."
The conclusion, albeit provisional, came as a surprise to many, because it did not seem like the TUE Subcommittee had spent enough time analyzing the second-round data. On the contrary, most of discussions have revolved around the topic of benefits and harm of the TUE itself.
When this "provisional" conclusion became known to English speakers via a online newspaper article on the Mainichi website, confusion ensued. English translation of the "interim report" is offered below so everyone can see the "basis" for the conclusion by the TUE Subcommittee. Translation of some of the analyses mentioned is to be posted separately.
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Note: This is a draft version. The final version is expected to have slightly different wording. (See the update at top.)
A summary of the subcommittee regarding the results of the Full-Scale
Screening of the Thyroid Ultrasound Examination (the second round)
June 3, 2019
Thyroid Ultrasound Examination Evaluation
Subcommittee by the
Oversight Committee for Fukushima
Health Management Survey
The Thyroid Ultrasound Examination
(herein, TUE) Evaluation Subcommittee by the Oversight Committee for Fukushima
Health Management Survey (herein, the Subcommittee) released an “Interim Summary
on the TUE” (herein, the Interim Summary) in March 2015 to report on the
results of the Initial Screening of the TUE (the first round) conducted from FY
2011 to FY 2013. The Interim Summary concluded that the results of the first
round “were unlikely to be the effects of radiation.”
At the 26th
Oversight Committee for Fukushima Health Management Survey (herein, the
Oversight Committee) held on February 20, 2017, a proposal was made to convene
the Subcommittee in order to summarize and evaluate the results of the Full-Scale
Screening of the TUE (the second round, FY 2014-2015). In response to this
proposal, the 7th Subcommittee was convened in conjunction with the
27th Oversight Committee on June 5, 2017, followed by the 8th
Subcommittee held with a new set of members on November 30, 2017. The
Subcommittee engaged in repeated deliberations over a total of 7 sessions, up
to the 13th Subcommittee held on June 3, 2019.
Based on the contents
of the deliberations, the Subcommittee summarized below the results of the second
round, opinions of the Subcommittee on the results, and issues for future consideration.
1 Results of the Full-Scale
Screening of the TUE (the second round)
The
second round that began in April 2014 covered approximately 380,000 Fukushima
residents, adding subjects born between April 2, 2011 and April 1, 2012 to the
first-round subjects born between April 2, 1992 and April 1, 2011. About 270,000
have participated as of June 30, 2017 (participation rates of 71% overall, 86.4%
in ages ≤ 17, 25.7% in ages ≥ 18), and 2227 (0.8%) were assessed the B test
results requiring a confirmatory examination and no one had the C test result (note:
requiring an immediate confirmatory examination). After undergoing fine-needle
aspiration cytology (FNAC) during the confirmatory examination, 71 were diagnosed
with confirmed or suspected malignancy (26.2/100,000; 32 males and 39 females;
average age 16.9 ± 3.2 years, age range 9-23 years; average age at the time of
the accident 12.6 ± 3.2 years, age range 5-18; average tumor diameter 11.1 ±
5.6 mm). (Note: 52 underwent surgery, revealing 51 papillary thyroid cancer and
1 other cancer.)
The detection
rate of thyroid cancer during the first round was several orders tens of times multiples of ten higher than
prevalence rate/proportion estimated from the Japanese cancer statistics data based on the
regional cancer registry. The thyroid cancer detection rate in the second round
was somewhat smaller than that in the first round but still several orders multiples of ten higher (than the cancer statistics data).
Detection rates of confirmed or suspected cancer showed no regional
difference in the first round. In the second round, a simple comparison without
adjusting for sex and age showed the highest detection rate in the 13 evacuated
municipalities, followed by Nakadori, Hamadori, and Aizu.
However,
detection rates of confirmed or suspected cancer are likely influenced by many
factors. When some of the factors were considered, the following tendencies
were observed.
- The detection rate of nodules with diameter of 5.1–10 mm was low in the 13 evacuated municipalities in the first round. Also, among subjects with the B test results in the second round, the proportion of the subjects whose first-round results were also B was low in the 13 evacuated municipalities. This suggests that the second-round results are affected by the first-round results.
- The longer the interval between the first and second rounds, the higher the FNAC rate and the detection rate of confirmed or suspected cancer. The longest average interval was observed in the 13 evacuated municipalities.
- FNAC rates have declined in successive years even in the first round. The second-round FNAC rate declined in the order of the 13 evacuated municipalities, Nakadori, Hamadori, and Aizu.
- When FNAC was conducted in the first round, FNAC rates and detection rates of confirmed or suspected cancer tended to be lower in comparison with the subjects who underwent no FNAC in the first round.
2 Regarding the preliminary
analysis on an association between thyroid cancer detection rates in the second
round and radiation doses
The above analysis has
shown that detection rates of confirmed or suspected cancer are influenced by many
factors other than sex and age at screening, such as screening year, FNAC
rates, screening interval since the first round, and whether FNAC was conducted
in the first round. Therefore, an evaluation of an association between thyroid
cancer detection rates and radiation doses calls for analyses that control these
factors.
For radiation doses, an
analysis was tentatively conducted with absorbed doses to the thyroid estimated
in different age groups and municipalities by United Nations Scientific
Committee on Effects of Atomic Radiation (UNSCEAR), which incorporate internal
exposure.
The analysis showed no
clear association between doses and thyroid cancer detection rates.
3 Findings
Proportions of the B test
results in the primary examination, recommended to advance to the confirmatory
examination, were larger with an older age at the time of the accident, and detection
rates of confirmed or suspected cancer were higher with an older age at the
time of the confirmatory examination. This is dissimilar to detection of many more
thyroid cancer in a younger age group after the Chernobyl accident. Detection
of more cancer with an increasing age is similar to cancer in general.
The male-to-female
ratio is close to 1:1, which is different from what tends to be observed in a
clinical setting (about 1:6). It has been reported that the male-to-female
ratio tends to be smaller in latent cancer and younger ages. Evaluation of an
association between the male-to-female ratio and radiation remains as a future
task.
A simple comparison of detection
rates of confirmed or suspected cancer in four regions appears to show differences,
but it is influenced by many factors such as screening year and screening
interval since the first round. Any analysis needs to take these factors into
consideration.
When factors that can
influence detection rates were adjusted as much as possible, analyses of an
association between doses and thyroid cancer detection rates, tentatively using
the absorbed doses to the thyroid estimated by UNSCEAR by age group and
municipality, revealed no consistent relationship between increasing doses and
increasing detection rates (dose-effect relationship).
Thus, at this time, no
association is seen between thyroid cancer detected in the second round and
radiation exposure.
4 Explanation to residents
covered by the TUE
The Subcommittee has advanced
discussion on contents of the explanation to residents covered by the TUE. It
is important to continue careful explanation of merits and demerits of the TUE,
so their understanding and consent may be gained before the TUE is administered.
5 Viewpoints for future
evaluation
The third round started
in FY 2016 and the fourth round in FY 2018, and their results need to be
incorporated into further analyses.
Also, participation
rates of the TUE are declining every year. In particular, a participation rate after
high school graduation is low with continuing decline expected in the future.
Moreover, it is possible that more cancer cases might be discovered outside the
TUE conducted as part of the Fukushima Health Management Survey.
This leads to the use
of regional and national cancer registries in order to identify cancer
incidence among residents covered by the TUE so an analysis could be conducted.
Further, in the future,
estimated thyroid exposure doses should be used in case control studies with
confounding factors adjusted, in order to evaluate an association between doses
and thyroid cancer incidence rates.
These are the
viewpoints that should be considered in advancing discussion at the
Subcommittee and the Oversight Committee in the future.
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