Young people's perspectives of thyroid cancer screening and its harms after the nuclear accident in Fukushima Prefecture: a questionnaire survey indicating opt-out screening strategy of the thyroid examination as an ethical issue.

BACKGROUND: Overdiagnosis of thyroid cancer has become a major global medical issue. Ultrasound-based thyroid cancer screening has promoted overdiagnosis, and recently international recommendations state that it should not be conducted, even after a nuclear accident. The Fukushima thyroid cancer screening program was initiated in 2011 as a health policy after the nuclear accident. The risk of radiation-induced thyroid cancer was unlikely given the low radiation levels, but the thyroid cancer screening program has continued at 2-year intervals with a relatively high participation rate and is now in its fifth round. It is therefore crucial to clarify whether those targeted for screening understand the disadvantages of screening, and to identify factors that influenced their decision to participate. METHODS: We conducted an anonymous mail-based questionnaire among young people from Fukushima Prefecture (subjects) and a neighboring prefecture that was not targeted for screening (non-subjects). We asked them about the significance of the thyroid cancer screening in Fukushima Prefecture, their reasons for accepting or refusing screening, their perception of the harms of screening, and their opinions on thyroid examination at school. We compared the results of the questionnaire between subjects and non-subjects and between examinees (who were screened) and non-examinees (who declined screening). RESULTS: Only 16.5% of respondents were aware of the harms associated with thyroid cancer screening, with most perceiving that the benefits outweighed the harms. Comparison of subjects' and non-subjects' responses showed there were no significant differences between the two groups. Among subjects, there were also no differences in responses between examinees and non-examinees. The most common reason for participation in screening was that the screening was conducted in schools and perceived as obligatory. CONCLUSIONS: These results highlighted a serious ethical issue in that school-based screening leads to making young people think that it is mandatory screening in an opt-out and default setting manner, with a lack of knowledge about the disadvantages of screening. Based on the autonomy of the subjects and the ethical principle of the post-disaster, surveys after a nuclear disaster should be conducted in an opt-in style without an opt-out style such as school-based screening.

Trajectory and factors of radiation risk perception of students aged 10-12 years at the time of the Fukushima Daiichi Nuclear Power Station accident.

Various studies have investigated radiation risk perceptions after the accident at the Fukushima Daiichi Nuclear Power Station. However, student surveys are limited. This study aimed to investigate the perception of radiation risk among students aged 18-20 years who were in the 5th and 6th grades of elementary school at the time of the accident. We surveyed students in the Fukushima Prefecture and outside the prefecture. Out of all the data, 59% of the respondents were living in the Fukushima Prefecture at the time of the accident and 41% outside the prefecture. Trajectory analysis showed that changes in anxiety levels over time since 2011 could be divided into five classes: (a) the anxiety was the highest, and this tendency persisted. (b) High at the beginning, but decreased more quickly than class 1. (c) High at the beginning, but it diminished quickly. (d) Not high, but did not diminish easily in later years. (e) Low from the beginning, and persisted. Multinomial logistic analysis showed that among students living outside the prefecture at the time of the accident, a significantly higher proportion was in groups 4 and 5 than in group 2. A significant proportion of boys were present in groups 3, 4 and 5. A significant proportion of students whose current educational institutions were inside the prefecture were present in group 3. The level of anxiety was associated with the academic course, but not with subjective knowledge of radiation. In contrast, in the qualitative analysis of the free text, 31% considered 'knowledge about radiation' as the reason for the reduction in anxiety level. At the time of the investigation, most young people were not anxious about radiation. However, approximately 20% still had strong anxiety. We established that continuous risk communication is necessary. Furthermore, that stabilization and support related to life in general is important.

Lessons learned from conducting disease monitoring in low-dose exposure conditions as a counter-measure after a nuclear disaster.

The complex disaster of the Great East Japan Earthquake and the Fukushima nuclear accident caused concern about their various health impacts. Many types of intervention are desired as a countermeasure, depending on the phase of the disaster cycle. The importance of developing and applying codes of conduct has recently been emphasized for post-disaster investigations. Thyroid examination as a type of cancer screening survey was launched from October 2011 after the Fukushima nuclear accident as part of the Fukushima Health Management Survey. In this article, we reviewed the results of three rounds of thyroid examination from 2011 to 2018, and summarized the points to consider in the health survey conducted after the Fukushima nuclear accident. Large-scale mass screening by ultrasound thyroid examination resulted in many cancer diagnoses, >200 cases from a large reservoir of thyroid cancer that goes mainly unnoticed without screening. To prevent the harms of such over-diagnosis, we should be aware of the disadvantage of mass-screening based on the expected natural history of thyroid cancer. A change in strategy from mass-screening to individual monitoring is urgently needed according to international recommendations that are opposed to thyroid ultrasound cancer screening even after a nuclear disaster. To guarantee autonomy and informed choice on post-disaster disease monitoring for residents in a disaster-zone, it is important to set protocol participation and on a voluntary code of conduct basis.

An ethical dimension to accident management and health surveillance.

Many radiation protection actions carry a multitude of direct and indirect consequences that can impact on the welfare of affected populations. Health surveillance raises ethical challenges linked to privacy and data protection, as well as questions about the net benefit of screening. The SHAMISEN project recognized these issues and developed specific recommendations to highlight ethical challenges. Following a brief overview of ethical issues related to accident management, this paper presents the SHAMISEN recommendations: R1 The fundamental ethical principle of doing more good than harm should be central to accident management; and R4 Ensure that health surveillance respects the autonomy and dignity of affected populations, and is sensitive to any inequity in the distribution of risks and impacts. While a holistic approach to accident management means that decisions will be complicated by different values, perceptions and uncertainties about outcomes, addressing ethical issues could help ensure that the assumptions and potential conflicts behind eventual decisions are as transparent as possible.

Nested matched case control study for the Japan Fukushima Health Management Survey's first full-scale (second-round) thyroid examination.

Since Fukushima nuclear accident in 2011, thyroid ultrasound examinations have been conducted. The first full-scale examination detected 71 thyroid-cancer cases. This study examined whether radiation exposure was associated with thyroid-cancer incidence.Subjects were participants in the baseline screening and newborns during the 2011 fiscal year. Under nested matched case-control study design, 10 controls per each case were selected by matching the age, sex, baseline screening results, and interval between examinations. With 3 dose levels of external radiation: 1.3 + mSv (upper), 0.8 to 1.3 (middle), and 0.0 to 0.8 (reference), we applied 2 logistic models adjusting for 3 participation-proportions (primary, secondary, and fine-needle aspiratory cytology), overweight, and the B-result of baseline screening (Model 1), and past medical history, family history of thyroid cancer, and frequencies of eating seafood and seaweed in addition to the parameters in Model 1 (Model 2). We examined each model in 3 ways: (a) excluding subjects with a missing radiation exposure dose; and substituting (b1) median or (b2) mean dose of the municipality with missing dose.Odds ratios (ORs) of middle-dose exposure were (a) 1.35 (0.46-3.94), (b1) 1.55 (0.61-3.96), and (b2) 1.23 (0.50-3.03) for Model 1, and (a) 1.18 (0.39-3.57), (b1) 1.31 (0.49-3.49), and (b2) 1.02 (0.40-2.59) for Model 2. For upper-dose exposure, similar results were obtained. Past medical history was significantly associated (odds ratio  = 2.04-2.08) with both (b1) and (b2) in Model 2.No significant associations were obtained between the external radiation exposure and thyroid-cancer incidence.

Time-dependent changes in FT4 and FT3 levels measured using mass spectrometry after an acute ingestion of excess levothyroxine in a case with hypothyroidism.

BACKGROUND: Thyrotoxicosis is common disorder among endocrine dysfunctions. It is not rare that the free thyroid hormone level exceeds the measurement range of immunoassay. Such extreme high concentration of free thyroid hormone is generally considered to be impossible to measure correctly because of changes in the balance between free hormones and binding proteins by dilution of serum. Using liquid chromatography-tandem mass spectrometry (LC-MS/MS), however, higher concentrations are able to be determined. CASE PRESENTATION: We present a case of a 21-year-old female with congenital hypothyroidism who had taken a total of 5 mg levothyroxine over three consecutive days following discontinuance of the medication for a month. Immunoassay performed 3 hours after the last ingestion showed that the patient's free thyroxine (FT4) was over 100 pmol/L and her free triiodothyronine (FT3) was 24.5 pmol/L. With a temporary cessation of levothyroxine, the patient was kept for observation without any other medication. Two days after the last ingestion, FT4 was still over 100 pmol/L and FT3 was increased to 28.8 pmol/L. After an additional 4 days, both FT4 and FT3 levels decreased. Through this period, no thyrotoxic symptom or physical sign had appeared. We also measured FT4 and FT3 levels in her cryopreserved serum by ultrafiltration LC-MS/MS. Her FT4 level measured by ultrafiltration LC-MS/MS on the visiting day and 2 days later were 160.0 and 135.5 pmol/L, respectively, indicating that the toxic dose of levothyroxine was partly changed to T3 during the 2 days. The FT3/FT4 ratios were revealed to be low, accounting for the patient's benign clinical course despite temporal toxic exposure to levothyroxine. It is implied that prior discontinuation of supplementary levothyroxine increases potential vacant binding sites for thyroid hormone as a buffer to prevent toxic T3 effect. CONCLUSION: It was helpful to clarify the time dependent changes in free thyroid hormone levels by ultrafiltration LC-MS/MS in discussing the clinical course in this case. Though mass spectrometry has a disadvantage in speed for routine laboratory use, its accurate measurement, particularly of levels exceeding the measurable range of the immunoassay, provides valuable information for more appropriate management of extreme thyrotoxicosis.

A multicenter, phase 2 study to evaluate the efficacy and safety of osilodrostat, a new 11ß-hydroxylase inhibitor, in Japanese patients with endogenous Cushing's syndrome other than Cushing's disease.

This phase 2, single-arm, open-label, dose-titration, multicenter study evaluated osilodrostat (11ß-hydroxylase inhibitor) in Japanese patients with endogenous Cushing's syndrome (CS) caused by adrenal tumor/hyperplasia or ectopic adrenocorticotropic hormone syndrome. The primary endpoint was percent change from baseline to week 12 in mean urinary free cortisol (mUFC) at the individual patient level. Of the nine patients enrolled in the study, seven completed the 12-week core treatment period and two discontinued at or prior to week 12 due to adverse events (AEs). Of the seven patients who completed 12 weeks of study treatment, two completed 48 weeks of study treatment. Median osilodrostat exposure was 12 weeks. Median (range) average dose including dose interruption (0 mg/day) was 2.143 (1.16-7.54) mg/day. Median (range, population) percentage change in mUFC was -94.47% (-99.0% to -52.6%, n = 7) at week 12. At week 12, 6/9 patients were complete responders (mUFC ≤ upper limit of normal [ULN]) and 1/9 was a partial responder (mUFC > ULN but decreased by ≥50% from baseline). Most frequent AEs were adrenal insufficiency (n = 7), gamma-glutamyl transferase increase, malaise, and nasopharyngitis (n = 3 each). Serious AEs were seen in four patients. No deaths occurred in this study. In conclusion, osilodrostat treatment led to a reduction in mUFC in all nine patients with endogenous CS other than Cushing's disease (CD), regardless of disease type, with >80% reduction seen in 6/7 patients at week 12. The safety profile was consistent with previous reports in CD patients, and the reported AEs were manageable.

Determination of the Kinetic Parameters for 123I Uptake by the Thyroid, Thyroid Weights, and Thyroid Volumes in Present-day Healthy Japanese Volunteers.

The purpose of this study was to evaluate the kinetic parameters that determine the uptake rate of radioiodide in the thyroid over 24 h after administration and to estimate thyroid volumes/masses of present-day Japanese. Methods: We determined the thyroid uptake rate of I in healthy male Japanese after oral administration (4.5-8.0 MBq) without iodine restriction. Masses of thyroid glands were collected in 2012-2016 during autopsies of 7,651 male and 3,331 female subjects. Volumes of thyroid glands were estimated by ultrasonography and magnetic resonance imaging in 52 male subjects. Results: The thyroid uptake rate of I for 24 h was 16.1 ± 5.4%. Kinetic model analysis was conducted to obtain the clearances (L h) for thyroid uptake and urinary excretion of I (0.499 ± 0.258 and 2.10 ± 0.39 L h, respectively). The masses of thyroid glands were on average 19.8 g (95% confidence interval of 18.3-19.5 g) and 15.5 g (95% confidence interval of 14.7-16.2 g) in male and female subjects aged 19-52 y, respectively. Volumes of thyroid glands estimated by ultrasonography and magnetic resonance imaging were 17.5 ± 5.2 and 14.2 ± 5.3 mL, respectively. In healthy Japanese, there has been no significant change for at least 50 y in the thyroid uptake of radioiodide over 24 h or in its kinetic parameters. These Japanese-specific kinetic parameters will allow quantitative estimation of the radiation exposure from the Fukushima accident and its variance during the individual's evacuation from or stay in Fukushima.

Factors Influencing the Proportion of Non-examinees in the Fukushima Health Management Survey for Childhood and Adolescent Thyroid Cancer: Results From the Baseline Survey.

BACKGROUND: After the Fukushima Daiichi Nuclear Power Plant accident, a preliminary ultrasound-based screening for thyroid cancer was conducted to establish a baseline for subsequent evaluations. In this survey, we assessed the relationship between the proportion of non-examinees and characteristics of the target populations. METHODS: After summarizing a regional difference of non-examinees among the population of 359,200 (primary evaluation) and 2,246 (confirmatory testing) individuals who were living in Fukushima Prefecture on March 11, 2011, we estimated odds ratios (ORs) for each characteristic, including age, sex, area of residence, and moving after the accident, based on the proportion of non-examinees for the primary examination and the confirmatory testing, using a multivariate logistic regression model. RESULTS: The dataset included 64,117 non-examinees (primary evaluation) and 194 (confirmatory testing). The logistic regression result indicated that girls were not likely to be non-examinees compared to boys, with adjusted OR of 0.80 (95% confidence interval [CI], 0.78-0.81) for the primary evaluation. Odds were lowest for children 6-10 years old (OR 0.26; 95% CI, 0.25-0.27), and higher for those 11-15 years old (OR 1.28; 95% CI, 1.25-1.32) and over 16 years old (OR 5.30; 95% CI, 5.16-5.43) when compared to children 0-5 years old. Individuals residing in the western part of the prefecture showed higher ORs. There was a higher proportion of non-examinees among those who moved after the accident compared to those who did not in the primary evaluation (OR 1.72; 95% CI, 1.64-1.79). CONCLUSIONS: In addition to demographic characteristics, a change of residence could be a potential factor that influenced the proportion of non-examinees. Our results will help proper interpretation of reports and prospective management of the survey.

External Radiation Dose, Obesity, and Risk of Childhood Thyroid Cancer After the Fukushima Daiichi Nuclear Power Plant Accident: The Fukushima Health Management Survey.

BACKGROUND: The 2011 Great East Japan Earthquake led to a nuclear accident at Fukushima Daiichi Nuclear Power Plant. This study examines the associations of radiation dose and lifestyle factors with incidence of thyroid cancer in Fukushima. METHODS: We designed a prospective study with 300,473 participants aged 18 years or younger, who underwent thyroid examinations from October 2011. Follow-up surveys were conducted through June 2017, and 245,530 participants (123,480 men and 122,050 women, 82% follow-up) received follow-up examinations. Fukushima Prefecture was divided into five areas based on individual external radiation dose. We calculated relative risks and 95% confidence intervals (CIs) for thyroid cancer in each area, with area of lowest dose as reference, using age-adjusted Poisson regression models. We also calculated risks associated with overweight and obesity. RESULTS: The incidence per 100,000 for Groups A (highest dose), B, C, D, and E (lowest dose) were 13.5, 19.2, 17.3, 9.0, and 8.3, respectively. Compared with Group E, the age-adjusted risks (95% CIs) were 1.62 (0.59, 4.47) for group A, 2.32 (0.86, 6.24) for group B, 2.21 (0.82, 5.94) for group C, and 1.02 (0.36, 2.86) for group D. Obesity was positively associated with thyroid cancer incidence; the multivariable-adjusted risk of thyroid cancer was 2.23 (1.01, 4.90) for obese individuals compared with nonobese individuals. CONCLUSION: Regional differences in radiation dose were not associated with increased risk of thyroid cancer among children in Fukushima within 4 to 6 years after the nuclear power plant accident. Obesity may be an important factor for further follow-up in Fukushima.

Incidence of Thyroid Cancer Among Children and Young Adults in Fukushima, Japan, Screened With 2 Rounds of Ultrasonography Within 5 Years of the 2011 Fukushima Daiichi Nuclear Power Station Accident.

Importance: Ultrasonographic (US) screening for thyroid cancer was performed in the Fukushima Health Management Survey after the 2011 Fukushima Daiichi nuclear power station accident. Clinical characteristics of thyroid cancers screened by US among children and young adults during the first 5 years after the accident were analyzed. Objectives: To evaluate the number of detected thyroid cancers by age group within 5 years of the Fukushima Daiichi nuclear power station accident and to compare the basic clinical characteristics and demographic patterns in first- and second-round examinations. Design, Setting, and Participants: In this observational study, 324 301 individuals 18 years or younger at the time of accident were included. Patients received a cytologic diagnosis of malignant or suspected malignant thyroid cancer during the first (fiscal years 2011-2013) or second round (fiscal years 2014-2015) of screening. Number of detected cases of cancer was evaluated, correcting for the number of examinees by age group at the time of the accident and for the incidence of detected cancers according to age group at the time of the screening (age groups were divided into 3-year intervals). Results were compared using the age-specific incidence of unscreened cancers from a national cancer registry. Main Outcomes and Measures: Clinical baseline characteristics of the patients and the age-specific number and incidence of thyroid cancers detected during the second round. Results: Among 299 905 individuals screened in the first round (50.5% male; mean [SD] age at screening, 14.9 [2.6] years), malignant or suspected thyroid cancer was diagnosed in 116. Among 271 083 individuals screened in the second round (50.4% male; age at screening, 12.6 [3.2] years), malignant or suspected thyroid cancer was diagnosed in 71. The most common pathologic diagnosis in surgical cases was papillary thyroid cancer (149 of 152 [98.0%]). The distribution pattern by age group at the time of the accident, where the number of detected thyroid cancer cases was corrected by the number of examinees, increased with older age in both screening rounds. This demographic pattern was similar between the first and second examinations. The distribution pattern of the incidence rate by age group at the time of screening in the second round also increased with older age. The incidence rate detected by screening was 29 cases per 100 000 person-years for those aged 15 to 17 years, 48 cases per 100 000 person-years for those aged 18 to 20 years, and 64 cases per 100 000 person-years for those aged 21 to 22 years. Conclusions and Relevance: Large-scale mass US screening of young people resulted in the diagnosis of a number of thyroid cancers, with no major changes in overall characteristics within 5 years of the 2011 Fukushima nuclear power station accident. These results suggest that US screening can identify many detectable cancers from a large pool of nonclinical and subclinical thyroid cancers among individuals of a relatively young age, in an age-dependent manner.

Spatial analysis of the geographical distribution of thyroid cancer cases from the first-round thyroid ultrasound examination in Fukushima Prefecture.

Following the Fukushima Daiichi Nuclear Power Plant (FNPP) accident on 11 March 2011, there have been concerns regarding the health impacts of the ensuing radioactive environmental contamination, which was spatially heterogeneous. This study aimed to assess the geographical variability of thyroid cancer prevalence among children and adolescents in Fukushima Prefecture. We computed the sex- and age-standardised prevalence ratio using 115 diagnosed or suspected thyroid cancer cases among approximately 300,000 examinees at the first-round ultrasound examination during 2011-2015 from 59 municipalities in the prefecture, under the Fukushima Health Management Survey. We applied flexibly shaped spatial scan statistics and the maximised excess events test on the dataset to detect locally anomalous high-prevalence regions. We also conducted Poisson regression with selected regional indicators. Furthermore, approximately 200 examinees showed positive ultrasound examination results but did not undergo confirmatory testing; thus, we employed simulation-based sensitivity tests to evaluate the possible effect of such undiagnosed cases in the statistical analysis. In conclusion, this study found no significant spatial anomalies/clusters or geographic trends of thyroid cancer prevalence among the ultrasound examinees, indicating that the thyroid cancer cases detected are unlikely to be attributable to regional factors, including radiation exposure resulting from the FNPP accident.

Mental health of nurses after the Fukushima complex disaster: a narrative review.

Work-related mental health impairment is recognized as a real problem in the context of helping responders, including health professionals, due to adverse health outcomes after a severe disaster. The Great East-Japan Earthquake, which occurred on 11 March 2011, was an unprecedented complex disaster that caused a nuclear accident at the Fukushima Daiichi Nuclear Power Plant (NPP). In addition to disaster stress and daily work, medical and health-care professionals, particularly nurses, provided counseling services to residents concerned about radiation health risks or mental health issues. This review focuses on the psychological aspects of the complex nuclear disaster, which was a combined artificial nuclear accident and natural disaster, and we investigated the psychological effects on hospital nurses associated with their experiences during the disaster. We looked at several investigations into the mental health of nurses after a nuclear disaster and in other situations. It was shown that mental health of nurses is impacted, not only after nuclear disasters but also in other circumstances. Furthermore, we noted the effects of extended periods of a heavy workload and daily life. Regarding anxiety about radiation exposure, nurses who had more knowledge of radiation tended to have better mental health, suggesting that education about the health risks of radiation exposure is important for health-care professionals. In summary, it is essential that nurses are provided with education about radiation exposure and its associated health risks, and also that there is a comprehensive approach to mental health care for nurses during the chronic phase of a disaster.

Findings of Thyroid Ultrasound Examination Within 3 Years After the Fukushima Nuclear Power Plant Accident: The Fukushima Health Management Survey.

Context: Childhood thyroid cancer is of great concern after the Fukushima nuclear power plant accident. Baseline analytical data on thyroid ultrasound examination (TUE) in children are important for future studies. Objective: We analyzed the age and sex distribution of findings from the TUEs of children and adolescents in the Fukushima Health Management Survey (FHMS). Design, Setting, and Participants: From October 2011 through March 2014, 294,905 participants aged 18 years or younger at the time of the earthquake voluntarily had TUEs in the first round of the FHMS. A secondary confirmatory examination was performed in 2032 subjects. Age- and sex-dependent prevalence and size of thyroid cysts, nodules, and cancers were analyzed. Main Outcome Measures: Age, sex, and size distribution of findings were analyzed. Results: Thyroid cysts, nodules, and cytologically suspected cancers were detected in 68,009, 1415, and 38 male subjects and in 73,014, 2455, and 74 female subjects, respectively. There was an age-dependent increase in the detection rate of thyroid nodules and cancer, but that of cysts reached a peak at 11 to 12 years. Sex affected the prevalence of thyroid nodules and cancers after the onset of puberty, but only a small difference was exhibited in that of cysts. Conclusions: The thyroid cancer detection rate in Fukushima was clarified, and the proportion of individuals with thyroid nodules and cysts varied substantially by age. The results of this study will contribute to future epidemiological research on nodular thyroid diseases in children and adolescents.

Comparative Analysis of the Growth Pattern of Thyroid Cancer in Young Patients Screened by Ultrasonography in Japan After a Nuclear Accident: The Fukushima Health Management Survey.

IMPORTANCE: Thyroid cancer generally grows at a very slow rate in adults, and overdiagnosis is a global issue. However, the detection of early-stage thyroid cancer by screening is not well described in young patients. To prevent overdiagnosis, it is essential to understand the natural course of thyroid cancer growth detection by ultrasonography screening in young patients. OBJECTIVE: To evaluate the natural progression of thyroid cancer in young patients. DESIGN, SETTING, AND PARTICIPANTS: An observational study evaluated changes in the diameter of malignant or suspected malignant thyroid tumors on 2 occasions. Changes in malignant thyroid tumor diameter were estimated during the observation period between the screening and confirmatory examinations in the first-round thyroid ultrasonography examination of the Fukushima Health Management Survey in patients younger than 21 years after a nuclear accident at a power plant in Fukushima, Japan. In total, 116 patients cytologically diagnosed with or suspected to have thyroid cancer were classified into 3 groups based on a greater than 10% reduction, a change of -10% to +10% in diameter, and a greater than 10% increase in tumor diameter. The association between tumor growth rate and tumor diameter was analyzed. The study was conducted from March 1, 2016, to August 6, 2017. MAIN OUTCOMES AND MEASURES: Tumor volume changes, the coefficient of growth of thyroid cancer in young patients, and the association between the observation period or tumor diameter and them. RESULTS: Of 116 patients, 77 were female; the mean age was 16.9 years (median, 17.5 years). The mean observation period was 0.488 (range, 0.077-1.632) years. No significant differences in age, sex, tumor diameter, observation period, or serum levels of thyrotropin and thyroglobulin were observed among the groups. Whereas tumor volume changes were not linearly correlated with the observation period (Pearson R = 0.121; 95% CI, -0.062 to 0.297), the coefficient of growth was significantly and negatively correlated with the tumor diameter in the screening examination (Spearman ρ = -0.183; 95% CI, -0.354 to -0.001), suggesting growth arrest after the initial proliferation phase. CONCLUSIONS AND RELEVANCE: Ultrasonography screening could reveal asymptomatic thyroid cancer that is falling into a growth arrest pattern in many young patients. Considering the long life expectancy, prevention of overdiagnosis necessitates careful long-term monitoring without immediate diagnosis for suspected noninvasive thyroid cancer.