Incident Thyroid Cancer Cases Research Articles

Thyroid cancer incidence in cohorts exposed in childhood to 131I released during the Windscale nuclear reactor accident at Sellafield, England, in 1957

A fire in one of the Windscale nuclear reactors at Sellafield (Cumbria, England) in October 1957 released 1,800 TBq of 131I (half-life, 8 days) to atmosphere. Measurements of 131I activity in thyroids of exposed children showed typical thyroid doses of tens of milligray, but with some exceeding 100 mGy. Radiation exposure in childhood is known to increase the risk of thyroid cancer. Consequently, an investigation was conducted into whether raised numbers of thyroid cancer cases occurred in those exposed to 131I as young children in Cumbria. A database of Cumbrian births from 1950 onwards allowed cohorts of 56,086 births during 1950–1958 and 137,444 births during 1959–1980 to be constructed, periods including children potentially exposed and unexposed, respectively, to 131I. Three areas of Cumbria with different 131I contamination levels were identified from monitoring data, and births assigned to these three areas for the two periods of birth. Members of these six sub-cohorts were linked to incident thyroid cancer cases in Great Britain during 1981–2020 using national cancer registration databases, providing thyroid cancer incidence rates. Incidence rate ratios (IRRs), with the lowest contamination area as a reference, were computed. No IRR differed discernibly from unity. For births during 1950–1958, the IRR for the combined highest and intermediate 131I contamination areas was 0.68 (95% confidence interval: 0.24, 1.56), and no case of thyroid cancer was found in the small cohort born in the highest contamination area. In conclusion, no increased risk of thyroid cancer in those exposed to 131I as young children in Cumbria in 1957 was detected. This study adds to the evidence on the long-term risk of thyroid cancer following childhood exposure to low and moderate levels of 131I, such as occurred following the Fukushima nuclear accident in 2011.

Sex-specific Associations between Body Mass Index and Thyroid Cancer Incidence among Korean Adults.

The potential differences by sex in the association between body mass index (BMI) and thyroid cancer risk remain unconfirmed. Data from the National Health Insurance Service-National Health Screening Cohort (NHIS-HEALS; 2002-2015; population size = 510,619) and the Korean Multi-center Cancer Cohort (KMCC) data (1993-2015; population size = 19,026) were used. We constructed Cox regression models, adjusted for potential confounders, to evaluate the association between BMI and thyroid cancer incidence in each cohort, and assessed the consistency of the results. In the NHIS-HEALS, 1,351 and 4,609 incident thyroid cancer cases occurred during the follow-up among men and women, respectively. Compared with BMI of 18.5-22.9 kg/m2, BMI of 23.0-24.9 [no. of cases = 410; HR, 1.25; 95% confidence interval (CI), 1.08-1.44], 25.0-29.9 (no. of cases = 522; HR, 1.32; 95% CI, 1.15-1.51), and ≥30.0 kg/m2 (no. of cases = 48; HR, 1.93; 95% CI, 1.42-2.61) were associated with an increased risk of incident thyroid cancer among males. Among females, BMI of 23.0-24.9 (no. of cases = 1,300; HR, 1.17; 95% CI, 1.09-1.26) and 25.0-29.9 (no. of cases = 1,406; HR, 1.20; 95% CI, 1.11-1.29) were associated with incident thyroid cancer. The analyses using the KMCC demonstrated results consistent with wider CIs. Sex differences in the associations between BMI and thyroid cancer incidence were observed in Korean cohorts. BMI <23 kg/m2 may help prevent incident thyroid cancer, especially among men.

Impact of social and economic factors on global thyroid cancer incidence and mortality.

The incidence of thyroid cancer has increased substantially over the past few decades and is partially explained by overdiagnosis. Geographical variations in incidence rates were reported to be related to national development status. This study aimed to gain deeper insights into global thyroid cancer burden by incorporating additional social and economic factors to account for cross-national disparities. We performed a multivariate analysis of age-standardized incidence and mortality data from the GLOBOCAN 2020 database for 126 countries that had more than 100 incident cases of thyroid cancer. The human development index (HDI), current health expenditure, and additional Global Health Observatory indicators were extracted from multiple sources. Age-standardized incidence was highly correlated with HDI (standardized coefficient beta = 0.523, 95% confidence interval [CI] = 0.275-0.771) among the countries studied. The prevalence of raised fasting blood glucose was associated with age-standardized mortality (beta = 0.277, 95% CI = 0.038-0.517). Generally, the mortality-to-incidence ratio was higher in males than in females. In multivariate analysis, HDI (beta = - 0.767, 95% CI = - 0.902 to - 0.633), current health expenditure (beta = 0.265, 95% CI = 0.137-0.394), and fine particulate matter (PM2.5) concentrations (beta = 0.192, 95% CI = 0.086-0.298) were associated with mortality-to-incidence ratios. National developments gauged by HDI explain the majority of the variation in incidence rates of thyroid cancer but play a smaller role in disparities in mortality rates. The association between air pollution and thyroid cancer outcomes warrants further investigation.

Association between Obesity Indexes and Thyroid Cancer Risk in Korean Women: Nested Case-Control Study.

Simple SummaryRegarding the association between obesity and thyroid cancer, most previous studies have focused only on body mass index (BMI), but other measures of obesity have not been studied much with inconsistent results. This study showed a significant association between increased abdominal obesity indexes, such as waist circumference (WC, ≥85.0 cm) and waist-height ratio (WHTR ≥ 0.5) as well as BMI (≥25.0 Kg/m2), and increased risk of thyroid cancer. In addition, people who had both abnormally obese levels of BMI and other obesity indexes including WC, waist–hip ratio, or WHTR showed an increased risk of thyroid cancer, compared to those with normal levels of BMI and each obesity index. These results provide evidence of the contribution of both total and central adiposity across the lifespan to thyroid cancer incidence. Risk factor modifications must be considered to explain the current thyroid cancer epidemic.Objective: This study aimed to identify the association between various obesity indexes, including waist circumference (WC), waist–hip ratio (WHR), waist–height ratio (WHTR), and BMI, and their combinations with body mass index (BMI) and thyroid cancer risk. Methods: Of the 65,639 participants who completed a follow-up survey of the Health Examinee Study (HEXA), a prospective cohort of the Korean Genome and Epidemiology Study, 412 female incident thyroid cancer cases, and 1648 birth year- and enrollment year-matched female controls were included. Multiple conditional logistic regression was used to estimate the association between obesity indexes and thyroid cancer risk. Results: The risk of developing thyroid cancer was increased by 1.37-fold (95% confidence interval (CI) = 1.03–1.81) higher in the obese BMI group (≥25.0 Kg/m2) compared to that in the normal BMI group (<23.0 Kg/m2). Obesity in terms of WC (≥85.0 cm) and WHTR (≥0.5) was associated with an increased risk of thyroid cancer (OR 1.55, 95% CI = 1.16–2.07; OR 1.37, 95% CI = 1.07–1.75, respectively). However, increased WHR levels did not show any significant association. Women with both obese levels of BMI (≥25.0 Kg/m2) and other obesity indexes (WC ≥ 85.0 cm, WHR ≥ 0.85, or WHTR ≥ 0.5) showed an increased risk of thyroid cancer with OR of 1.63 (95% CI = 1.14–2.31), 1.49 (95% CI = 1.05–2.12), and 1.42 (95% CI = 1.04–1.94), compared to those with normal levels of BMI and each obesity index. Conclusion: These results provide evidence of the contribution of both total and central adiposity across the lifespan of thyroid cancer incidence. Risk factor modifications must be considered to explain the current thyroid cancer epidemic.

Dairy consumption and incident risk of thyroid cancer in Japan: a pooled analysis of the Miyagi Cohort Study and the Ohsaki Cohort Study.

The impact of dairy consumption on thyroid cancer is unclear. The purpose of this study was to elucidate the association between dairy consumption and the risk of thyroid cancer in Japanese people. The association between dairy consumption and the risk of thyroid cancer in Japanese people was examined by conducting a pooled analysis of two prospective studies of residents in Miyagi Prefecture, Japan. Data from 64,340 men and women aged 40-79years registered in the Miyagi Cohort Study in 1990 and in the Ohsaki Cohort Study in 1994 were analyzed. Dairy consumption was assessed at baseline using a self-administered food frequency questionnaire and was divided into quartiles based on the weight (in grams) of total dairy consumption per day. During 1,075,018 person-years of follow-up, there were 190 incident cases of thyroid cancer (29 men and 161 women). The hazard ratios (HRs) and 95% confidence intervals (CIs) for thyroid cancer incidence in the highest quartile of dairy consumption compared with the lowest quartile were 0.83 (95% CIs 0.28-2.43, P-trend = 0.823) for men and 0.67 (95% CIs 0.42-1.06, P-trend = 0.056) for women. After stratification for BMI, a decreased risk was observed in women with BMI ≥ 25kg/m2 (HRs: 0.37, 95% CIs 0.18-0.79, P-trend = 0.010). Dairy consumption is inversely associated with the risk of thyroid cancer in women with BMI ≥ 25kg/m2.

Low-Level Environmental Mercury Exposure and Thyroid Cancer Risk Among Residents Living Near National Industrial Complexes in South Korea: A Population-Based Cohort Study.

Background: Previous studies suggested that mercury may be linked to thyroid cancer due to its bioaccumulation in the thyroid gland, but no studies have evaluated the association between mercury exposure and thyroid cancer risk. We examined the relationship between mercury exposure and thyroid cancer risk, with the potential modification of hematological parameters. Methods: We performed a secondary analysis of a prospective cohort study among residents living near industrial complexes in South Korea (recruited from 2003 to 2011). Incident thyroid cancer cases (C73, ICD-10 code) were identified from the National Cancer Registry and Statistics Korea. Urinary mercury concentrations were measured using thermal decomposition amalgamation atomic absorption spectrometry (TDA-AAS). Cox proportional hazards regression models (adjusted for age, sex, educational level, smoking status, and employment) were used to estimate the hazard ratio (HR) and confidence interval [CI] between mercury exposure and the incidence of thyroid cancer. Results: We documented 69 cases of thyroid cancer in a total of 5213 participants during follow-up (median 8.7 years). The geometric mean of urinary mercury concentration was 1.8 μg/L for thyroid cancer cases and 1.2 μg/L for noncases (p for difference = 0.001). After adjusting for potential confounders, those in the highest tertile of urinary mercury levels had a twofold higher risk of thyroid cancer (HR = 1.97 [CI 1.03 - 3.80] in the highest tertile vs. the lowest tertile, p for trend = 0.043). This association was stronger for those with lower mean corpuscular volume and mean corpuscular hemoglobin status. Conclusions: Urinary mercury concentration was positively associated with the risk of thyroid cancer among residents living near national industrial complexes, and this association was influenced by red blood cell indices status. These results provide some evidence suggesting the adverse effects of environmental metal pollution in the development of thyroid cancer.

Associations between artificial light at night and risk for thyroid cancer: A large US cohort study.

Light at night (LAN) inhibits nighttime secretion of melatonin and may cause circadian disruption, which may be a risk factor for cancer. Recent studies have linked high LAN exposure with elevated breast cancer risk. Given that breast cancer may share a common hormone-dependent etiology with thyroid cancer and that circadian rhythms play a role in regulating thyroid function, the authors hypothesized that exposure to LAN is positively associated with thyroid cancer incidence. This study examined the association between LAN and thyroid cancer incidence in the National Institutes of Health-American Association of Retired Persons Diet and Health Study. LAN exposure was estimated from satellite data and was linked to residential addresses at the baseline. Incident thyroid cancer cases were ascertained via linkage to state cancer registries. Cox regression was used to determine the relationship between LAN and thyroid cancer risk, with adjustments made for sociodemographic, lifestyle, and other environmental factors. Among 464,371 participants, a positive association was found between LAN and thyroid cancer risk. Specifically, in comparison with the lowest quintile of LAN, the highest quintile was associated with a 55% increase in risk (hazard ratio [HR], 1.55; 95% confidence interval [CI], 1.18-2.02). The association was primarily driven by papillary thyroid cancer and was stronger in women (HR, 1.81; 95% CI, 1.26-2.60) than men (HR, 1.29; 95% CI, 0.86-1.94). In women, the association was stronger for localized cancer, whereas in men, the association was stronger for a more advanced stage. Results were consistent across different tumor sizes. LAN was positively associated with thyroid cancer risk. Future studies are needed to confirm this association and identify underlying biological mechanisms.

Toluene concentrations in the blood and risk of thyroid cancer from National Industrial Complexes: a population-based cohort study

Background/AimAlthough monocyclic aromatic hydrocarbons are classified as definite or possible carcinogen, studies on toluene with thyroid cancer risk are limited. This study was conducted to examine potential associations between blood toluene and the incidence risk of thyroid cancer, and the effect modification of living environment among residents living near industrial complex.MethodsWe conducted a prospective cohort study using data from the Industrial Monitoring Project of South Korea. Study participants in living near National Industrial Complexes were recruited from January 2003 to 2010. Incidence and mortality cases of thyroid cancer (C73, ICD-10 code) was identified through National Cancer Registry and Statistics Korea, respectively. Blood toluene was measured by gas chromatography mass spectrometry. We used Cox proportional hazards regression models to estimate incidence rate ratios (IRRs) and 95% confidence intervals (CI) between blood toluene and thyroid cancer risk.ResultsThe geometric means of the toluene concentration in blood were 0.62 μg/L for cases and 0.29 μg/L for noncases. During the follow-up (median 8.7 years), 32 incident cases of thyroid cancer were diagnosed. After adjusting for potential confounders, a positive association between blood toluene and thyroid cancer was found (IRR=3.38, 95% CI = 1.12-10.24 in the highest tertile vs. the lowest tertile, p-value=0.03). This positive association was stronger in people living near a road (≤50 meters) (IRR= 5.14, 95% CI = 1.12-23.67 in the highest tertile vs. the lowest tertile, p-value=0.04).ConclusionsBlood toluene may be positively associated with the incidence risk of thyroid cancer. Moreover, this association of blood toluene with thyroid cancer risk may also be stronger in people living near a road.

Thyroid cancer incidence near nuclear sites in Belgium: An ecological study at small geographical level.

In Belgium, variations in thyroid cancer incidence were observed around the major nuclear sites. The present ecological study investigates whether there is an excess incidence of thyroid cancer among people living in the vicinity of the four nuclear sites at the smallest Belgian geographical level. Rate ratios were obtained from a Bayesian hierarchical model for areas of varying sizes around the nuclear sites. Focused hypothesis tests and generalized additive models were performed to test the hypothesis of a gradient in thyroid cancer incidence with increasing levels of surrogate exposures. No evidence was found for more incident cases of thyroid cancer near the two nuclear power plants. Regarding the two industrial and research nuclear sites, no evidence for a higher incidence in the vicinity of Mol‐Dessel was observed, whereas a slightly nonsignificant higher incidence was found in the close vicinity of Fleurus. In addition, significant gradients for thyroid cancer incidence were observed with the different types of surrogate exposure considered in the 20 km area around the site of Fleurus (decreasing distance, increasing wind direction frequency and increasing exposure to estimated hypothetical radioactive discharges of iodine‐131). In the investigation at the smallest Belgian geographical level, variations in thyroid cancer incidence were found around the Belgian nuclear sites. Significant exposure–response relationships were also observed for the site of Fleurus. Further investigations into these findings could be useful to allow inferring causal relationships on the origin of variations in incidence and to provide information at the individual level.

Role of the Mechanisms of Detection in the Increased Risk of Thyroid Cancer: A Retrospective Cohort Study in an HMO in Buenos Aires.

Background Two hypotheses attempt to explain the increase of thyroid cancer (TC) incidence: overdetection by excessive diagnostic scrutiny and a true increase in new cases brought about by environmental factors. Changes in the mechanism of detection and the risk of incidentally diagnosed TC could result in an increase of TC incidence. Methods Retrospective cohort study. We identified incident cases of TC from the pathological reports of patients in a HMO and review of clinical records. The results were analyzed in two periods: 2003-2007 and 2008-2012. Incidence rates expressed per 100,000 person-years (with 95% CI) and relative risk of incidence rates of incidental and nonincidental TC were estimated. Results The relative risk of incidentally detecting a thyroid cancer in 2008-2012 compared to 2003-2007 was 6.06 (95%CI 1.84-20.04). Clinical evaluations detected 31 (75.6%) cancers in the period 2003-2007 and 70 (51.8%) cancers in the period 2008-2012 (p<0.007). Although tumor median size was significantly lower in the period 2008-2012 (10 vs. 14 mm, p<0.03), tumors greater than 40 mm (4.3%) were only present in 2008-2012. The female/male ratio decreased between analyzed periods from 8 (3-21) to 4 (3-7). Conclusions Our findings partially support the hypothesis of increased incidence due to overdetection but do not explain the changes in the increase of larger tumors and decrease in the female/male ratio, which could be secondary to the influence of unidentified environmental factors.

Alcohol Consumption and Risk of Thyroid Cancer: A Population Based Case-Control Study in Connecticut.

Studies examining the association between alcohol consumption and thyroid cancer risk have been inconsistent, in part due to varying types and amounts of alcohol consumption, incomplete information on confounders, and variations in genetic susceptibility in study populations. The present study analyzed data from a population-based case-control study in Connecticut in 2010-2011 including 462 histologically confirmed incident thyroid cancer cases and 498 population-based controls. Unconditional logistic regression was used to estimate associations between alcohol consumption and risk of thyroid cancer. Potential confounding variables were age, gender, race, education, body mass index, family history of cancer among first-degree relatives, history of benign thyroid disease, smoking status, and physical activity. Ever consumption of alcohol was associated with a reduced risk of thyroid cancer (OR=0.71, 95% CI: 0.54-0.95). The younger age at initiation and increasing duration of alcohol consumption were also associated with a reduced risk of thyroid cancer in a dose-dependent manner (P for trend=0.041 and 0.0065, respectively). Compared to people who never drank alcohol, people who drank alcohol for >31years were 50% less likely to develop thyroid cancer (OR=0.50, 95% CI: 0.32-0.80). Alcohol consumption was associated with a reduced risk of papillary thyroid cancer (OR=0.66, 95% CI: 0.49-0.88) and thyroid cancer with lager tumor size (>1cm), but no significant association was found between alcohol consumption and non-papillary thyroid cancer or thyroid microcarcinoma. Analyses stratified by specific subtypes of alcohol demonstrated an inverse association for beer(OR=0.69, 95% CI: 0.49-0.96) and wine consumption (OR=0.71, 95% CI: 0.53-0.96) as compared to participants who never consumed alcohol, but no significant association was found for liquor consumption (OR=0.75, 95% CI: 0.53-1.04). The study findings suggest an inverse association between alcohol consumption and risk of thyroid cancer. Future mechanistic study is warranted to elucidate the underlying mechanisms.

Benign breast disease and risk of thyroid cancer.

It has been suggested that breast and thyroid diseases may be linked. The aim of this study was to investigate the association between benign breast disease and subsequent risk of thyroid cancer. Postmenopausal women (n=133,875) aged 50-79years were followed up for a mean of 14years. Benign breast disease was defined by history of biopsy. Incident thyroid cancer cases were confirmed by medical record review. Multivariable Cox proportional hazard modeling was used to estimate hazard ratios. There were 370 incident thyroid cancer cases during the follow-up period. Compared to women without BBD, women with BBD had a significant increased risk of thyroid cancer after adjusting for potential confounders (HR 1.38 95% CI 1.10-1.73), especially for women with more than two biopsies (HR 1.59 95% CI 1.10-2.26). There were no significant differences in thyroid tumor size, stage or histologic types between women with and without BBD. Our large prospective study observed that postmenopausal women with BBD had an increased risk for thyroid cancer compared with women without BBD. A more detailed investigation of thyroid cancer risk according to different subtypes of benign breast disease is needed to better understand the association observed between thyroid and benign breast diseases.

Performance of claims-based algorithms for identifying incident thyroid cancer in commercial health plan enrollees receiving antidiabetic drug therapies

BackgroundThyroid cancer incidence is increasing in the United States (US) and many other countries. The objective of this study was to develop and evaluate algorithms using administrative medical claims data for identification of incident thyroid cancer.MethodsThis effort was part of a prospective cohort study of adults initiating therapy on antidiabetic drugs and used administrative data from a large commercial health insurer in the US. Patients had at least 6 months of continuous enrollment prior to initiation during 2009–2013, with follow-up through March, 2014 or until disenrollment. Potential incident thyroid cancers were identified using International Classification of Diseases, 9th Revision (ICD-9) diagnosis code 193 (malignant neoplasm of the thyroid gland). Medical records were adjudicated by a thyroid cancer specialist. Several clinical variables (e.g., hospitalization, treatments) were considered as predictors of case status. Positive predictive values (PPVs) and 95% confidence intervals (CIs) were calculated to evaluate the performance of two primary algorithms.ResultsCharts were requested for 170 patients, 150 (88%) were received and 141 (80%) had sufficient information to adjudicate. Of the 141 potential cases identified using ≥1 ICD-9 diagnosis code 193, 72 were confirmed as incident thyroid cancer (PPV of 51% (95% CI 43–60%)). Adding the requirement for thyroid surgery increased the PPV to 68% (95% CI 58-77%); including the presence of other therapies (chemotherapy, radio-iodine therapy) had no impact. When cases were required to have thyroid surgery during follow-up and ≥2 ICD-9 193 codes within 90 days of this surgery, the PPV was 91% (95% CI 81-96%); 62 (82%) of the true cases were identified and 63 (91%) of the non-cases were removed from consideration by the algorithm as potential cases.ConclusionsThese findings suggest a significant degree of misclassification results from relying only on ICD-9 diagnosis codes to detect thyroid cancer. An administrative claims-based algorithm was developed that performed well to identify true incident thyroid cancer cases.

Occupational exposure to pesticides and other biocides and risk of thyroid cancer

ObjectivesTo assess the associations between occupational exposure to biocides and pesticides and risk of thyroid cancer.MethodsUsing data from a population-based case–control study involving 462 incident thyroid cancer cases and 498...

Use of Dietary Vitamin Supplements and Risk of Thyroid Cancer: A Population-Based Case-Control Study in Connecticut.

A population-based case-control study in Connecticut was conducted during 2010-2011 among 462 histologically confi rmed incident thyroid cancer cases and 498 population-based controls. Dietary supplement intake was ascertained through in-person interviews and a food frequency questionnaire. Multivariate unconditional logistic regression models were used to estimate the risk of thyroid cancer and dietary supplement use. Overall, no statistically signifi cant associations were observed between dietary supplementation and thyroid cancer risk. Stratifi ed analyses revealed a suggestive protective effect on risk of papillary microcarcinoma among longterm (> 10 years) use of multivitamins (OR = 0.59, 95 % CI: 0.33, 1.04) and calcium supplementation (OR = 0.45, 95 % CI: 0.22, 0.93). An increased risk of large papillary thyroid cancers (tumor size > 1 cm) was observed among short-term (< 5 years) users of calcium supplements (OR = 2.24, 95 % CI: 1.30, 3.88). No signifi cant associations were observed between supplementation and overall thyroid cancer risk. The different associations between calcium supplements and risk of papillary thyroid cancer by tumor size warrant further investigation.

Hysterectomy, Oophorectomy, and Risk of Thyroid Cancer.

Estrogen has been suggested as a risk factor for thyroid cancer. The aim of this study is to examine the associations between hysterectomy, bilateral salpingo-oophorectomy (BSO), and incidence of thyroid cancer. This was a prospective cohort study. The study was conducted at 40 clinical centers in the United States. A total of 127 566 women aged 50-79 were enrolled in the Women's Health Initiative during 1993-1998. Hysterectomy and BSO were self-reported. Incident thyroid cancer cases were confirmed by medical record review. Three hundred forty-four incident thyroid cancer cases were identified during an average of 14.4 years of follow-up. Compared with women without hysterectomy, women with hysterectomy, regardless of ovarian status, had a significantly higher risk of thyroid cancer (hazard ratio 1.46 [95% confidence interval 1.16-1.85]). Hysterectomy with BSO was not associated with a lower risk for thyroid cancer compared with hysterectomy alone. Among women with hysterectomy alone, hormone therapy use was associated with lower risk of thyroid cancer (hazard ratio 0.47 [95% confidence interval 0.28-0.78]). However, we did not observe significant associations between hormone therapy use and thyroid cancer in women without hysterectomy or women with hysterectomy plus BSO. Our large prospective study observed that hysterectomy, regardless of oophorectomy status, was associated with increased risk of thyroid cancer among postmenopausal women. In addition, our data did not support the hypotheses that exogenous estrogen is a risk factor or that estrogen deprivation is a protective factor for thyroid cancer. Further research is needed to clarify whether these apparent associations may be due to shared risk factors between indications for hysterectomy and thyroid cancer.

Do US thyroid cancer incidence rates increase with socioeconomic status among people with health insurance? An observational study using SEER population-based data

ObjectivesThe US thyroid cancer incidence rates are rising while mortality remains stable. Trends are driven by papillary thyroid cancer (PTC), the predominant cancer subtype which has a very good prognosis....

The contribution of radiotherapy to subsequent thyroid cancer risk may be confined to a subgroup of breast cancer patients

Based on the “National Health Insurance Research Database (NHIRD)” of Taiwan, Sun Li-Min et al. found that the increased risk of thyroid cancer among breast cancer survivors of Taiwanese women was not related to radiotherapy (RT).1 However, this conclusion may be assertive considering the neglects of the following issues. First, thyroid cancer incidence of the whole population from the Cancer Registry data should be described and compared. Although the controls were randomly selected from NHIRD which covered approximately 99% of the residents, it seems not be proved that the control was a representative sample of the whole population. Moreover, we noticed that the thyroid cancer incidence of the control group (2.16 per 10,000 person-year) was different from those in other reports.2, 3 Second, the incubation period for induction of thyroid cancer by RT should be considered. The authors used the index date (the first treatment day of RT for the patients) as the beginning of the follow-up, then some incident thyroid cancer cases occurred immediately after the index date were probably not caused by RT. Therefore, thyroid cancer patients who were diagnosed in a period of time (e.g. half a year) after the index date may need to be excluded. Simultaneously, a sensitive test to compare the results before and after the exclusion would be helpful. This phenomenon has implications with regard to nondifferential misclassification, which usually leads underestimation of the incidence risk ratios.4 Third, the risk of thyroid cancer did increase in some sub groups. For example, Table 3 showed that the adjusted hazard ratios (HRs) of thyroid cancer risk for women receiving RT was 1.97 among those aged older than 55 years, almost twice as much as those receiving no RT (reference), although it did not reach a statistical level, which was probably due to a small sample size. Moreover, Table 5 showed that those receiving RT had a significant higher risk of thyroid cancer compared with patients without RT (aHR = 1.93, 95%, CI = 1.09–3.40) among breast cancer survivors without chemotherapy, which was not found in women with chemotherapy. This phenomenon suggests that RT may be involved in subsequent thyroid cancer development among breast cancer survivors, and this association may be modified by other treatment factors, like chemotherapy. In fact, for the whole study subjects, a nonsignificant 28% increase of thyroid cancer risk was observed (Table 2). Finally, for the several stratification analyses, a heterogeneity test or an interaction (multiplicative or additive models) test would be beneficial to verify whether the differences between strata were sampling errors or real differences.5, 6 Yours sincerely, Wei Lin, Fang-Mei Ren and Ze-Fang Ren

Electric Blanket Use and Risk of Thyroid Cancer in the Women’s Health Initiative Observational Cohort

Thyroid cancer disproportionally affects more women than men. The aim of this study was to assess whether exposure to extremely low frequency electric magnetic fields from electric blankets (EBs) was associated with the development of thyroid cancer. Data were analyzed from 89,527 women who participated in the Women’s Health Initiative Observational Study and who responded to questions concerning prior use of EBs. During a mean follow-up of 12.2 years, 190 incident cases of thyroid cancer were identified. We estimated the hazard ratio (HR) and 95 percent confidence interval (CI) of incident thyroid cancer associated with EB use by Cox’s proportional hazard model, adjusted for selected covariates. A majority, 57 percent, of the women in the cohort reported the use of EBs while sleeping and/or for warming the bed before sleep. No association was found between use of EBs and subsequent risk of thyroid cancer (HR = 0.98, 95 percent CI 0.72–1.32). Duration of EB use measured in years, months, or hours had no effect on risk. These results did not change when the cases were limited to papillary thyroid cancer, the most frequently occurring histologic type. The results of this study do not support possible health hazards of EBs in regards to thyroid cancer risk.

Randomization to screening for prostate, lung, colorectal and ovarian cancers and thyroid cancer incidence in two large cancer screening trials.

BackgroundThyroid cancer incidence has increased significantly over the past three decades due, in part, to incidental detection. We examined the association between randomization to screening for lung, prostate, colorectal and/or ovarian cancers and thyroid cancer incidence in two large prospective randomized screening trials.MethodsWe assessed the association between randomization to low-dose helical CT scan versus chest x-ray for lung cancer screening and risk of thyroid cancer in the National Lung Screening Trial (NLST). In the Prostate Lung Colorectal and Ovarian Cancer Screening Trial (PLCO), we assessed the association between randomization to regular screening for said cancers versus usual medical care and thyroid cancer risk. Over a median 6 and 11 years of follow-up in NLST and PLCO, respectively, we identified 60 incident and 234 incident thyroid cancer cases. Cox proportional hazards regression was used to calculate the cause specific hazard ratios (HR) and 95% confidence intervals (CI) for thyroid cancer.ResultsIn NLST, randomization to lung CT scan was associated with a non-significant increase in thyroid cancer risk (HR = 1.61; 95% CI: 0.96–2.71). This association was stronger during the first 3 years of follow-up, during which participants were actively screened (HR = 2.19; 95% CI: 1.07–4.47), but not subsequently (HR = 1.08; 95% CI: 0.49–2.37). In PLCO, randomization to cancer screening compared with usual care was associated with a significant decrease in thyroid cancer risk for men (HR = 0.61; 95% CI: 0.49–0.95) but not women (HR = 0.91; 95% CI: 0.66–1.26). Similar results were observed when restricting to papillary thyroid cancer in both NLST and PLCO.ConclusionOur study suggests that certain medical encounters, such as those using low-dose helical CT scan for lung cancer screening, may increase the detection of incidental thyroid cancer.