Post-Chernobyl thyroid carcinoma in Belarus children and adolescents: comparison with naturally occurring thyroid carcinoma in Italy and France

Aggressiveness of Differentiated Thyroid Carcinoma in Pediatric Patients Younger Than 16 years: A Propensity Score-Matched Analysis

Background

The biological behavior of thyroid cancer in children has been known to be different from that in adults. We sought to understand the differences between DTC presentation in pediatric (<16 years) and adult patients, to guide better prognosis and clinical treatments.

Methods

This retrospective study included 48 pediatric patients younger than 16 years who underwent initial thyroid surgery and were diagnosed with DTC between January 1992 and December 2014 at Yonsei University in Seoul, South Korea. For a 1:4 propensity score-matched analysis, adult patients with matched sex and cancer size were included.

Results

The mean age was 12.54 ± 3.01 years. Total thyroidectomy (70.8%) without lateral lymph node dissection (47.9%) was the most commonly performed surgery. Central (73.9%) and lateral neck node metastases (62.5%) were common; distant metastasis was observed in 2 (4.2%) patients and recurrence occurred in 11 (22.9%). In propensity score-matched analysis, central lymph node metastasis and lateral neck node metastasis were significantly more frequent in pediatric patients. Symptoms were more common in the pediatric group than in the adult group (p < 0.001). In stratified cox regression, pediatric patients were more likely to experience recurrence [HR 5.339 (1.239–23.007)]. In stratified log-rank analysis, recurrence-free survival was significantly different between the adult and pediatric groups (p = 0.0209).

Conclusion

DTC in the pediatric group revealed more aggressive patterns than in the adult group with the same cancer size. Central lymph node metastasis and lateral neck node metastasis were more frequent. Stratified log-rank analysis revealed that recurrence was significantly higher in pediatric patients than in matched adult patients.

Ionizing Radiation Deregulates the MicroRNA Expression Profile in Differentiated Thyroid Cells

BACKGROUND

Ionizing radiation (IR) is a well-known risk factor for papillary thyroid cancer, and it has been reported to deregulate microRNA expression, which is important to thyroid carcinogenesis. Therefore, this study investigated the impact of IR on microRNA expression profile of the normal thyroid cell line (FRTL-5 CL2), as well as its effect on radiosensitivity of thyroid cancer cell lines, especially the human anaplastic thyroid carcinoma cell line (8505c).

METHODS

The global microRNA expression profile of irradiated FRTL-5 CL2 cells (5 Gy X-ray) was characterized, and data were confirmed by quantitative real-time polymerase chain reaction evaluating the expression of rno-miR-10b-5p, rno-miR-33-5p, rno-miR-128-1-5p, rno-miR-199a-3p, rno-miR-296-5p, rno-miR-328a-3p, and rno-miR-541-5p in irradiated cells. The miR-199a-3p and miR-10b-5p targets were validated by quantitative real-time polymerase chain reaction, Western blot, and luciferase target assays. The effects of miR-199a-3p and miR-10b-5p on DNA repair were determined by evaluating the activation of the protein kinases ataxia-telangiectasia mutated, ataxia telangiectasia, and Rad3-related and the serine 39 phosphorylation of variant histone H2AX as an indirect measure of double-strand DNA breaks in irradiated FRTL-5 CL2 cells. The impact of miR-10b-5p on radiosensitivity was analyzed by cell counting and MTT assays in FRTL-5 CL2, Kras-transformed FRTL-5 CL2 (FRTL KiKi), and 8505c cell lines.

RESULTS

The results reveal that miR-10b-5p and miR-199a-3p display the most pronounced alterations in expression in irradiated FRTL-5 CL2 cells. Dicer1 and Lin28b were validated as targets of miR-10b-5p and miR-199a-3p, respectively. Functional studies demonstrate that miR-10b-5p increases the growth rate of FRTL-5 CL2 cells, while miR-199a-3p inhibits their proliferation. Moreover, both of these microRNAs negatively affect homologous recombination repair, reducing activated ataxia-telangiectasia mutated and Rad3-related protein levels, consequently leading to an accumulation of the serine 39 phosphorylation of variant histone H2AX. Interestingly, the overexpression of miR-10b-5p decreases the viability of the irradiated FRTL5-CL2 and 8505c cell lines. Consistent with this observation, its inhibition in FRTL KiKi cells, which display high basal expression levels of miR-10b-5p, leads to the opposite effect.

CONCLUSIONS

These results demonstrate that IR deregulates microRNA expression, affecting the double-strand DNA breaks repair efficiency of irradiated thyroid cells, and suggest that miR-10b-5p overexpression may be an innovative approach for anaplastic thyroid cancer therapy by increasing cancer cell radiosensitivity.

Intrinsic LINE-1 Hypomethylation and Decreased Brca1 Expression are Associated with DNA Repair Delay in Irradiated Thyroid Cells

Exposure to ionizing radiation greatly increases the risk of developing papillary thyroid carcinoma (PTC), especially during childhood, mainly due to gradual inactivation of DNA repair genes and DNA damages. Recent molecular characterization of PTC revealed DNA methylation deregulation of several promoters of DNA repair genes. Thus, epigenetic silencing might be a plausible mechanism for the activity loss of tumor suppressor genes in radiation-induced thyroid tumors. Herein, we investigated the impact of ionizing radiation on global methylation and CpG islands within promoter regions of homologous recombination (HR) and non-homologous end joining (NHEJ) genes, as well as its effects on gene expression, using two well-established normal differentiated thyroid cell lines (FRTL5 and PCCL3). Our data reveal that X-ray exposure promoted G₂/M arrest in normal thyroid cell lines. The FRTL5 cells displayed a slower kinetics of double-strand breaks (DSB) repair and a lower long interspersed nuclear element-1 (LINE-1) methylation than the PCCL3 cells. Nevertheless, acute X-ray exposure does not alter the expression of genes involved in HR and NHEJ pathways, apart from the downregulation of Brca1 in thyroid cells. On the other hand, HR and NHEJ gene expressions were upregulated in radiation-induced senescent thyroid cells. Taken together, these data suggest that FRTL5 cells intrinsically have less efficient DNA DSB repair machinery than PCCL3 cells, as well as genomic instability, which could predispose the FRTL5 cells to unrepaired DSB lesions and, therefore, gene mutations.

Previous External Beam Radiation Treatment Exposure Does Not Confer Worse Outcome for Patients with Differentiated Thyroid Cancer

BACKGROUND

Radiation exposure, especially in childhood, is known to increase the risk for the development of thyroid cancer. However, the prognosis of patients with thyroid cancer with a history of radiation treatment exposure remains unclear.

METHODS

One hundred and sixteen patients with a previous history of radiotherapy in the head and neck region were identified from an institutional database of 3664 patients with differentiated thyroid cancer treated between 1986 and 2010. Using the Kaplan-Meier method, disease-specific survival and recurrence-free survival were compared between patients with (RT; n = 116) and without (No RT; n = 3509) a prior history of radiation exposure.

RESULTS

The median ages of the RT and No RT cohorts were 52 and 47 years. The median follow-up for both groups was 54 months. Patients who had a prior history of radiation treatment exposure were more likely to be male (38.8% vs. 26.9%; p = 0.005) and older than 45 years of age (67.2% vs. 53.9%; p = 0.005). Other patient, tumor, and treatment characteristics were similar between the groups. There was no difference in the five-year disease-specific survival of the RT and No RT patients (97.4% vs. 98.7%; p = 0.798). The five-year recurrence-free survival was also similar between the RT and No RT patients (97.8% vs. 94.9%; p = 0.371).

CONCLUSION

The findings suggest that differentiated thyroid cancer patients with a history of prior radiation treatment exposure have similar outcomes to those with no history of head and neck radiation exposure.

2017 Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease During Pregnancy and the Postpartum

BACKGROUND

Thyroid disease in pregnancy is a common clinical problem. Since the guidelines for the management of these disorders by the American Thyroid Association (ATA) were first published in 2011, significant clinical and scientific advances have occurred in the field. The aim of these guidelines is to inform clinicians, patients, researchers, and health policy makers on published evidence relating to the diagnosis and management of thyroid disease in women during pregnancy, preconception, and the postpartum period.

METHODS

The specific clinical questions addressed in these guidelines were based on prior versions of the guidelines, stakeholder input, and input of task force members. Task force panel members were educated on knowledge synthesis methods, including electronic database searching, review and selection of relevant citations, and critical appraisal of selected studies. Published English language articles were eligible for inclusion. The American College of Physicians Guideline Grading System was used for critical appraisal of evidence and grading strength of recommendations. The guideline task force had complete editorial independence from the ATA. Competing interests of guideline task force members were regularly updated, managed, and communicated to the ATA and task force members.

RESULTS

The revised guidelines for the management of thyroid disease in pregnancy include recommendations regarding the interpretation of thyroid function tests in pregnancy, iodine nutrition, thyroid autoantibodies and pregnancy complications, thyroid considerations in infertile women, hypothyroidism in pregnancy, thyrotoxicosis in pregnancy, thyroid nodules and cancer in pregnant women, fetal and neonatal considerations, thyroid disease and lactation, screening for thyroid dysfunction in pregnancy, and directions for future research.

CONCLUSIONS

We have developed evidence-based recommendations to inform clinical decision-making in the management of thyroid disease in pregnant and postpartum women. While all care must be individualized, such recommendations provide, in our opinion, optimal care paradigms for patients with these disorders.

Comprehensive Survey Results of Childhood Thyroid Ultrasound Examinations in Fukushima in the First Four Years After the Fukushima Daiichi Nuclear Power Plant Accident

BACKGROUND

Thyroid nodules and cancers are rare in children compared with adults. However, after the 1986 Chernobyl Nuclear Power Plant accident, a rapid increase in childhood thyroid cancer was observed. To avoid any confusion and misunderstanding of data obtained in Fukushima after the 2011 nuclear accident, baseline prevalence of thyroid nodules and cancers should be carefully assessed with standardized criteria systematically, and comprehensively applied to the population perceived to be at risk.

AIMS

Under the official framework of the Fukushima Health Management Survey, the thyroids of children in Fukushima were examined using ultrasound, and the results collected in the first four years after the nuclear accident were analyzed in order to establish a baseline prevalence of childhood thyroid abnormalities, especially cancer.

SUBJECTS AND METHODS

Of 367,685 people aged 18 years or younger as of April 1, 2011, who were living in Fukushima Prefecture at the time of the accident, 300,476 underwent thyroid ultrasound screening. Of those, 2108 subjects with thyroid nodules were further examined using an advanced ultrasound instrument, with standardized criteria applied to determine the need for fine-needle aspiration cytology (FNAC). FNAC results determined the need for surgery and histological confirmation of the cytological diagnosis.

RESULTS

Of the 2108 rescreened subjects, 543 underwent FNAC, of whom 113 were diagnosed with malignancy or suspected malignancy. Subsequently, 99 patients underwent surgical resection, revealing 95 cases of papillary thyroid cancer, three poorly differentiated cancers, and one benign nodule. The overall prevalence of childhood thyroid cancer in Fukushima was determined to be 37.3 per 100,000 with no significant differences between evacuated and non-evacuated areas. Thyroid cancer patients had external exposure estimates of <2.2 mSv during the first four months.

CONCLUSIONS

The high prevalence of childhood thyroid cancer detected in this four-year study in Fukushima can be attributed to mass screening. It clearly exceeds what is found incidentally anywhere else. Direct comparisons with any other results, even those from cancer registries, are not meaningful because of differences in methodology.

2015 American Thyroid Association Management Guidelines for Adult Patients with Thyroid Nodules and Differentiated Thyroid Cancer: The American Thyroid Association Guidelines Task Force on Thyroid Nodules and Differentiated Thyroid Cancer

BACKGROUND

Thyroid nodules are a common clinical problem, and differentiated thyroid cancer is becoming increasingly prevalent. Since the American Thyroid Association's (ATA's) guidelines for the management of these disorders were revised in 2009, significant scientific advances have occurred in the field. The aim of these guidelines is to inform clinicians, patients, researchers, and health policy makers on published evidence relating to the diagnosis and management of thyroid nodules and differentiated thyroid cancer.

METHODS

The specific clinical questions addressed in these guidelines were based on prior versions of the guidelines, stakeholder input, and input of task force members. Task force panel members were educated on knowledge synthesis methods, including electronic database searching, review and selection of relevant citations, and critical appraisal of selected studies. Published English language articles on adults were eligible for inclusion. The American College of Physicians Guideline Grading System was used for critical appraisal of evidence and grading strength of recommendations for therapeutic interventions. We developed a similarly formatted system to appraise the quality of such studies and resultant recommendations. The guideline panel had complete editorial independence from the ATA. Competing interests of guideline task force members were regularly updated, managed, and communicated to the ATA and task force members.

RESULTS

The revised guidelines for the management of thyroid nodules include recommendations regarding initial evaluation, clinical and ultrasound criteria for fine-needle aspiration biopsy, interpretation of fine-needle aspiration biopsy results, use of molecular markers, and management of benign thyroid nodules. Recommendations regarding the initial management of thyroid cancer include those relating to screening for thyroid cancer, staging and risk assessment, surgical management, radioiodine remnant ablation and therapy, and thyrotropin suppression therapy using levothyroxine. Recommendations related to long-term management of differentiated thyroid cancer include those related to surveillance for recurrent disease using imaging and serum thyroglobulin, thyroid hormone therapy, management of recurrent and metastatic disease, consideration for clinical trials and targeted therapy, as well as directions for future research.

CONCLUSIONS

We have developed evidence-based recommendations to inform clinical decision-making in the management of thyroid nodules and differentiated thyroid cancer. They represent, in our opinion, contemporary optimal care for patients with these disorders.

Radiation exposure and the risk of pediatric thyroid cancer

It has been more than three years since the unprecedentedly massive earthquake and tsunami struck eastern Japan on March 11, 2011, and the large accident occurred at the Fukushima Daiichi Nuclear Power Plant. To investigate the influence of radiation exposure, thyroid ultrasonography has been provided preliminarily for 360,000 children who lived in Fukushima Prefecture at the time of the accident. As of September 2013, 59 children had been diagnosed with thyroid cancer by fine-needle aspiration cytology, and 34 children had been treated surgically and ultimately diagnosed with papillary thyroid cancer. Here, I would like to describe the characteristics of pediatric thyroid cancer and typical thyroid images obtained by ultrasonography.

Environmental Toxicology: Children at Risk

Children today live in a world that is vastly different from a few generations ago. While industrialization has maximized (for many) children’s opportunities to survive, develop and enjoy high levels of health, education, recreation, and fulfillment, it has also added significant challenges to their development.

Clinical and pathologic features of "sporadic" papillary thyroid carcinoma registered in the years 2005 to 2008 in children and adolescents of Belarus

BACKGROUND

A systematic analysis of the clinical and pathologic patterns of childhood "sporadic" thyroid carcinoma in Belarus, in the absence of the "Chernobyl radioactive iodine factor," has never been performed. The aim of this study was to establish the essential features of "sporadic" papillary thyroid carcinoma (PTC) in Belarusian children and adolescents, and the relationship of tumor pathology to extrathyroidal extension (ETE) and lymph node metastases.

METHODS

This was a retrospective population-based study with assessment of histological samples of 119 cases of thyroid cancer in Belarusian children and adolescents of 0-18 years old registered during 2005-2008 years. Sporadic PTC was noted in 94 children who were not exposed to the Chernobyl radiation release. None of the 119 cases of thyroid were follicular thyroid cancer.

RESULTS

The incidence rate of PTC was 1.13 per 100,000 persons. The median age at diagnosis was 15.1 years with fourfold predominance of diagnosis in female patients. Relapse was detected in 2% of cases with median follow-up of 4.2 years. Median tumor size was 12 mm. Three percent of the cases of PTC had multifocal growth. The classical variant of PTC was registered in 46% of the patients with thyroid cancer, the follicular variant of PTC was noted in 20% of the cases. The percent of rare types of PTC (tall cell and diffuse sclerosing) were equal to that for solid PTCs (13%, 12%, and 10%, respectively). Adolescents had a pure papillary carcinoma more often compared to children who represented tumors with mixed papillary/follicular patterns more frequently (p<0.05). Two-thirds of the patients with PTC had regional lymph node metastases. ETE was established in 39 of 74 patients in whom ETE could be assessed by morphology. Multivariate analysis showed that lymphatic invasion was the strongest independent factor associated with both ETE (p<0.0001) and lymph node metastases (p<0.0001).

CONCLUSION

In 2005-2008, sporadic thyroid cancer in children of Belarus was represented by high prevalence of PTC and absence of follicular thyroid cancer. Sporadic cases of PTC in Belarus were characterized by smaller tumor size, a small number of cases with multifocal growth, an equal number of rare types and solid PTCs, a relatively high prevalence of pure papillary variant of PTC in adolescents, and a low frequency of early relapses. A high frequency of ETE and lymph node metastases was detected. The strongest morphologic factor associated with both of them was lymphatic invasion.

Clinical-pathological changes in differentiated thyroid cancer (DTC) over time (1997-2010): data from the University Hospital "Maggiore della Carità" in Novara

Differentiated thyroid cancer (DTC) is an important clinical entity in our population (Novara, Piedmont, Italy) which is characterized by important environmental influences, as iodine deficiency (ID) and subsequent supplementation, thyroiditis and occupational exposure. To evaluate the features of DTC in our population 20 years after the iodine-prophylaxis pondering the effects of the introduction of the new guidelines for diagnosis and management of DTC after 2005. 322 patients [244 females, age: mean (±SD) 53.8 ± 15.8 years] treated for DTC in a tertiary care center between 1997 and 2010 were retrospectively evaluated. Medical history, demographics, and pathological features were considered. Patients were subdivided into two groups: A (n = 139, diagnosis 1997–2005) and B (n = 183, diagnosis 2006–2010). The population of group A showed a mild ID, while normal iodine status was recorded in group B. A significant increase in histological tumor-associated thyroiditis was found from group A to B (p = 0.021). Recurrent or persistent diseases were found to be correlated with lymph nodes metastases and/or a distant disease at diagnosis, stimulated thyroglobulin levels at the first follow-up and an additional radioiodine therapy. Twenty percent of our patients were females employed in textile industries. The tumor-related inflammation and the occupational exposure should be considered as important factors in the pathogenesis of DTC. Further studies are required in order to confirm our findings.

Clinical features, treatment, and long-term outcome of papillary thyroid cancer in children and adolescents without radiation exposure

BACKGROUND

Cancer of the thyroid gland is rare in children and adolescents. A history of neck irradiation is a well-established risk factor for tumor development, and most previous reports focused on cases that were induced by radiation exposure. We present here a retrospective review of the clinical features, treatment, and long-term outcome of children and adolescents with papillary thyroid cancer (PTC) without a history of radiation exposure who were treated at our institution over a period of ~50 years.

METHODS

We retrospectively investigated 142 PTC patients without an irradiation history who were younger than 20 years of age when treated from 1961 to 2005 (17 males and 125 females; mean age = 16.3 ± 2.7 years; follow-up = 21.8 ± 12.0 years). The clinicopathological results were evaluated using the medical records. Disease-free survival (DFS) and cause-specific survival (CSS) were assessed with the Kaplan-Meier method and compared with the log-rank test. Parametric analyses were performed using Student's t test and nonparametric analyses were performed using the Mann-Whitney U test.

RESULTS

At diagnosis, three patients had distant lung metastasis and 33 had gross neck lymph node (LN) metastasis. All patients were treated with surgery (hemi/partial thyroidectomy in 45 patients, subtotal thyroidectomy in 85, total thyroidectomy in 12, no LN dissection in 50, central compartment dissection in 20, and modified radical neck dissection in 72), and postoperative external beam radiation therapy was administered to 59. Postoperative ablative therapy using I(131) was not performed in this series. Recurrence was found for regional LN (n = 25), lung (n = 9), remnant thyroid (n = 5), and others (n = 4). DFS and CSS at 40 years were 74.1 and 97.5%, respectively. DFS was significantly worse in patients aged <16 years with a family history of thyroid cancer, preoperative neck gross LN metastasis, maximum tumor diameter, and extrathyroidal invasion. Preoperative gross neck LN metastasis and distant metastasis at diagnosis were significant factors for CSS. No other factors contributed to DFS and CSS. When the clinical features of children and adolescents were compared, the incidence of preoperative gross neck LN metastasis and distant metastasis at diagnosis and tumors with a maximum diameter >10 mm were significantly higher in the children group than in the adolescent group. DFS was significantly shorter in the children group than in the adolescent group, but no significant difference was found in CSS between these two groups.

CONCLUSIONS

The prognosis of PTC in children and adolescents is excellent, regardless of the extent of thyroidectomy and LN dissection. We recommend that only children or adolescents with preoperative gross neck LN metastasis and distant metastasis at diagnosis should be subjected to postoperative ablative therapy.

Thyroid cancer characteristics in the population surrounding Three Mile Island

OBJECTIVES/HYPOTHESIS

To determine differences in disease characteristics between the thyroid cancer populations in the area around the Three Mile Island (TMI) nuclear power plant and the rest of the state of Pennsylvania.

STUDY DESIGN

Retrospective cross-sectional study.

METHODS

Data from the Pennsylvania Cancer Registry from 1985 to 2008 were reviewed and information regarding age at diagnosis, sex, race, residential status, county of residence, thyroid pathology, thyroid surgery, and staging was recorded. Dauphin, Lancaster, and York counties were defined as the TMI area.

RESULTS

Records of 26,357 thyroid cancer patients were reviewed, with 2,611 patients within the TMI area. A higher proportion of papillary thyroid cancer (P < .001) and lower proportion of follicular thyroid cancer (P < .001) were noted in the TMI area population. Thyroid cancer cases from the TMI area were found to be more likely to be diagnosed before the age of 65 years (P < .001), be Pennsylvania born (P < .001), be well differentiated (P < .001), be <10 mm in size (P < .001), and be localized without spread (P < .001). Although the TMI area shows a higher incidence of thyroid cancer as compared to the rest of the state, this was not statistically significant.

CONCLUSIONS

The TMI population showed a higher proportion of papillary thyroid cancer and less aggressive pathology and earlier diagnosis compared to the rest of Pennsylvania. No statistically significant difference in thyroid cancer incidence was noted. Overall, the study does not show a clear link with more advanced thyroid cancer and proximity to the TMI nuclear reactors.

Thyroid incidentaloma

Because of emerging investigation modalities many of the thyroid lesions are picked up and that poses a big dilemma about management of such lesions. Majority of these lesions especially in iodine-deficient regions, are not significant and may be only followed up without any active treatment but, sometimes the small lesions may be microcarcinoma. This article discusses about the reliability of clinical examination of neck for detection of such lesions, the controversy of such lesion being benign or malignant, and how to evaluate these lesions and the recommendation as per American Thyroid Association guidelines.

Clinical presentation and clinical outcomes in Chernobyl-related paediatric thyroid cancers: what do we know now? What can we expect in the future?

Over the last 20 years, nearly 5000 cases of differentiated thyroid cancer have been diagnosed and treated in the regions of Russia, Ukraine and Belarus in young people previously exposed to the Chernobyl radioactive fallout during childhood. At diagnosis, 60-70% of the Chernobyl-related paediatric thyroid cancers had clinically evident cervical lymph node metastases (N1) and 10-15% had distant metastases (M1). Despite early reports suggesting that the paediatric thyroid cancer cases that developed after exposure to Chernobyl fallout were particularly aggressive, it now seems that the initial presentation and early clinical course of most of these cases are very similar to both non-radiation-associated paediatric thyroid cancers and thyroid cancers that arise after exposure to external beam irradiation. Over an average clinical follow-up period of about 10 years, the disease-specific mortality rate in these paediatric thyroid cancer cases that developed after the Chernobyl accident is quite low (1% or less). As would be expected in paediatric thyroid cancer, short-term recurrence rates range from 7 to 28% in published reports (mean 17%). However, long-term studies of paediatric thyroid cancer suggest that although the 30 year disease-specific mortality rate should be about 1%, the risk of developing structural disease recurrence is nearly 30% (of which 80% are expected to be locoregional recurrences and 20% are probably new distant metastases). Projected over 30 years of follow-up, a 1% disease-specific mortality in this cohort of 5000 patients would equate to about 50 deaths directly attributable to thyroid cancer. However, a 30% recurrence rate would also mean that about 1500 patients may develop a clinically meaningful recurrence that would need to be diagnosed and treated. It is imperative that we continue to work with our colleagues in Belarus, Ukraine and Russia to ensure that this large volume of patients destined to develop clinically significant recurrences are diagnosed and treated in a timely manner. Ready access to modern disease detection tools (serum thyroglobulin, postoperative neck ultrasonography, cytology/pathology support, and radioactive iodine scanning) and treatments (surgery for recurrent disease, radioactive iodine therapy) in their major academic centres are mandatory if we expect to achieve the excellent clinical outcomes that should be seen when paediatric thyroid cancer recurrence is diagnosed early and treated appropriately.

(131)I therapy in patients with benign thyroid disease does not conclusively lead to a higher risk of subsequent malignancies

Due to its excellent tolerability and low incidence of side effects, 131I therapy has been the treatment of choice for benign thyroid diseases for over 60 years. A potentially increased risk of malignancies due to this therapy is however still subject of debate.

AIM

To review the literature pertaining to 131I therapy of benign thyroid diseases in order to establish whether there is an increased incidence of, or increased mortality due to malignancies of the thyroid or other organs.

METHODS

In order to allow for sufficient long-term follow-up time after 131I therapy, only literature after 1990 was reviewed. Two criteria were applied to consider an increased incidence of malignancies linked to 131I therapy: a) there should be a latency period of at least 5 years between 131I therapy and the observation of an increased risk b) an elevated risk should increase with increasing radiation exposure.

RESULTS

A total of 7 studies reporting cancer incidence and / or mortality in 4 different patient collectives spanning a total of 54510 patients over an observation period varying from 2-49 years were found. Although some studies detected a slightly increased risk for malignancies of the thyroid or the digestive system, others did not find these effects - while other studies even reported a slightly lower risk of malignant (thyroid) disease after 131I therapy for benign thyroid diseases.

CONCLUSION

As over 60 years of experience has thus far failed to produce conclusive evidence to the contrary, it can be concluded that there is no increased risk of malignancies after 131I therapy for benign thyroid disease.

Frequency of undetected thyroid nodules in a large I-131-exposed population repeatedly screened by ultrasonography: results from the Ukrainian-American cohort study of thyroid cancer and other thyroid diseases following the Chornobyl accident

BACKGROUND

Imperfect detection on screening tests can lead to erroneous conclusions about the natural history of thyroid nodules following radiation exposure. Our objective was to assess in a repeatedly screened I-131-exposed population the frequency with which a thyroid nodule could be retrospectively identified on ultrasonography studies preceding the one on which it was initially detected.

METHODS

A cohort of over 13,000 young people exposed to fallout from Chornobyl underwent ultrasonography screening at 2-year intervals from 1998 to 2007. The study group consisted of screening examinations on which a thyroid nodule was detected following one or more prior negative examinations. In the study group there were 48 cancers and 92 benign nodules. For each of these 140 index studies a comparison set was created containing all available prior studies plus (to test for bias) negative studies from control subjects. While viewing the index study, three independent reviewers scored the comparison studies for the presence and size of a preexisting nodule. Detection rates were compared for true priors versus controls, for cancer versus benign, and for histologic subtypes of papillary carcinoma.

RESULTS

A preexisting nodule was identified by at least one reviewer in 24.0% of the true prior versus 8.3% of the controls and by all three reviewers in 11% versus 1% (Fisher's exact test, p < 0.0001). There was no significant difference in detection rates between cancers and benign nodules (22.4% vs. 24.7%, p = 0.411). There was no correlation between time from prior to index study and change in nodule size for either malignant or benign nodules (r = 0.01, NS). There were no differences in detection rates or size among papillary cancer subtypes. Reviewers could not distinguish between true priors and controls.

CONCLUSIONS

These findings, showing significant rates of undetected benign and malignant nodules and no evidence for rapid growth, suggest that conclusions drawn from screening studies about the frequency of late-developing, rapidly growing thyroid nodules following radiation exposure should be interpreted with caution.

Revised American Thyroid Association management guidelines for patients with thyroid nodules and differentiated thyroid cancer

BACKGROUND

Thyroid nodules are a common clinical problem, and differentiated thyroid cancer is becoming increasingly prevalent. Since the publication of the American Thyroid Association's guidelines for the management of these disorders was published in 2006, a large amount of new information has become available, prompting a revision of the guidelines.

METHODS

Relevant articles through December 2008 were reviewed by the task force and categorized by topic and level of evidence according to a modified schema used by the United States Preventative Services Task Force.

RESULTS

The revised guidelines for the management of thyroid nodules include recommendations regarding initial evaluation, clinical and ultrasound criteria for fine-needle aspiration biopsy, interpretation of fine-needle aspiration biopsy results, and management of benign thyroid nodules. Recommendations regarding the initial management of thyroid cancer include those relating to optimal surgical management, radioiodine remnant ablation, and suppression therapy using levothyroxine. Recommendations related to long-term management of differentiated thyroid cancer include those related to surveillance for recurrent disease using ultrasound and serum thyroglobulin as well as those related to management of recurrent and metastatic disease.

CONCLUSIONS

We created evidence-based recommendations in response to our appointment as an independent task force by the American Thyroid Association to assist in the clinical management of patients with thyroid nodules and differentiated thyroid cancer. They represent, in our opinion, contemporary optimal care for patients with these disorders.

Treatment of Graves' hyperthyroidism: evidence-based and emerging modalities

Currently there are three well-established treatment options for hyperthyroid Graves' disease (GD): antithyroid drug therapy with thionamides (ATD), radioactive iodine treatment with (131)I, and thyroid surgery. This article reviews the current evidence so the reader can evaluate advantages and disadvantages of these treatment modalities. Surgery is rarely used, except for patients who have a large goiter or ophthalmopathy. Fewer than 50% of patients treated with ATD remain in long-term remission. Therefore, radioactive iodine is used increasingly. No data as yet support the routine use of biologic therapies (eg, rituximab). Prospective, randomized studies comparing available and any novel therapeutic options for GD are needed. The focus of these studies should include, but not be limited to, cost and quality of life.

Clinical behavior of radiation-induced thyroid cancer: factors related to recurrence

BACKGROUND

Whether thyroid cancer is more aggressive in radiation-exposed patients is not resolved. The frequency of aggressive features in post-Chernobyl patients suggests this may be the case. Our aim was to address this question by re-examining the pattern of risk factors for recurrence of thyroid cancers found in a cohort exposed to external radiation.

METHODS

The study population was drawn from a cohort of 4296 people, followed since 1974, who were treated before the age of 16 with conventional external radiation for benign conditions of the head and neck between 1939 and the early 1960s. The study group consisted of 390 patients who had surgically verified thyroid cancer. Potential risk factors for recurrence were evaluated by proportional hazards analysis.

RESULTS

Fifty patients had recurrences an average of 8.7 years after diagnosis while the other 340 patients were followed for an average of 19.7 years. The sooner after radiation exposure the cancer occurred, the more likely it was to recur (hazard ratio, 0.96/year; 95% confidence interval [CI] 0.91-0.99). Taking into account the effect of the onset of screening in 1974, the features predictive of recurrence were younger age at the initial diagnosis (hazard ratio, 0.95/year; 95% CI, 0.91-0.99) and the size of the thyroid cancer (hazard ratio, 1.2/cm; 95% CI, 1.0-1.6).

CONCLUSION

Although not based on a direct comparison, we conclude that thyroid cancers following external radiation exposure are not, on average, more aggressive than other thyroid cancers. The similarity of risk factors for recurrence suggests that they should be treated and followed in the same way as non-radiation-induced thyroid cancers.

Thyroid examination in highly radiation-exposed workers after the Chernobyl accident

CONTEXT

Radioactive contamination from the Chernobyl nuclear accident that happened on the morning of 26th April 1986 had a major impact on thyroid health in the Belarus region.

OBJECTIVE

Observational study of a cohort of 99 adults, most strongly exposed to ionizing radioactivity.

DESIGN, SETTING AND PATIENTS

Observational study performed between 1998 and 2000. The cohort comprised 99 workers (92 male) of the Chernobyl nuclear power plant. Examination including physical examination, ultrasonography of the thyroid gland and measurement of serum free thyroxin (fT(4)), free triiodothyronine (fT(3)) and TSH. Anti-thyroperoxidase (anti-TPO), antithyroglobulin (anti-Tg) antibodies and thyroid stimulating immunoglobulin were also determined.

MAIN OUTCOME MEASURES

The impact of exposure to high-dose radiation, including radioactive iodine, on the thyroid gland was examined.

RESULTS

Levels of fT(4) in all probands were within the normal World Health Organization-defined range. Elevated levels of fT(3) were found in two workers (2%), high titres of anti-TPO and anti-Tg antibodies were present in four subjects (4%). Mild hypothyroidism was present in one patient. Enlargement of the thyroid gland was observed in 17 workers (17%). There was no evidence of clinically overt thyroid cancer.

CONCLUSIONS

The Chernobyl accident showed surprisingly little impact on the thyroid in a cohort of workers strongly exposed to radiation. Our data suggest an age-dependent heterogeneity in response to the short-lived radioiodine isotopes and favours long-term follow-up analysis.

Prognosis and risk stratification in young papillary thyroid carcinoma patients

Controversies remain regarding to the therapeutic methods of papillary thyroid cancer (PTC) in young patients. TNM staging and other risk evaluation system are not perfectly applicable for all young PTC patients in view of disease outcome. The aims of this study are to identify the clinical presentations, prognostic factors and risk analysis methods. From January, 1977, to June, 2006, seventy-seven patients with primary PTC younger than 20 years old at Chang Gung Medical Center in Taiwan were enrolled in this retrospective study. The patients were classified as disease-free or non-disease-free according to presence or absence of distant metastases or local recurrence at the end of follow-up. Clinical data of these patients were analyzed and compared. The average follow-up period was 10.3 years. Two patients died of PTC during the follow-up period; one died of brain metastasis, and one died of airway obstruction. Patients undergoing total thyroidectomy, especially those with disease beyond the thyroid, had better outcomes than patients not undergoing total thyroidectomy (p = 0.003). Moreover, the DeGroot clinical classification system was a better predictor of prognosis than TNM (p<0.001 vs p = 0.007). Our results suggest that prognosis for PTC is not worse in younger patients. However, patients who had undergone total thyroidectomy might have a better prognosis. Clinical classification is a good alternative classification system for predicting disease outcome in young PTC patients. Patients with confined intrathyroid lesion (<or=T2, N0, M0) may be regarded "low risk" PTC patients.

Clinical features and therapeutic implication of papillary thyroid microcarcinoma

Papillary thyroid microcarcinomas (PTMs) are small tumors (< or =1 cm of diameter) that belong to the well-differentiated low-risk carcinomas of the thyroid, which are characterized by benign behavior, probably of little clinical significance, and do not affect patients' survival. They are found in otherwise normal thyroids or in multinodular goiters with a clinical frequency varying substantially according to different series. Sometimes, PTM may be associated with lymph node metastases at presentation and/or locoregional recurrences during follow-up. Distant metastases are extremely rare, but have been reported. Although deaths related to PTM are almost unknown, PTM raises therapeutic implications. This review addresses the issue of definition, treatment, and follow-up of PTM.

Dosimetric analysis of thyroid doses from total cranial irradiation

The purpose was to estimate the radiation dose to the thyroid from total cranial irradiation with parallel opposed lateral fields of 1.25 MeV gamma rays of (60)Co, to represent the current treatment modality, and with 6 MV photon beams derived from a linear accelerator. The mean thyroid doses were measured using thermoluminescence dosemeters in the Rando phantom with two cranial irradiation set-ups: (1) the lateral beams were angled by rotating the collimator to avoid irradiation of the lens and healthy tissues and (2) the lateral beams were not angled, and shielding blocks were used to protect the lens and healthy tissues. For a cranial dose of 18 Gy, thyroid doses for child patients for (60)Co with the open and blocked fields were 0.27 and 0.32 Gy, respectively. With 6 MV, the thyroid dose was less than the doses for (60)Co open and blocked cranial fields by 17 and 10%, respectively. Unblocked cranial fields and a high-energy photon beam should be preferred for cranial irradiation of children.

Thyroid cancer incidence and survival among European children and adolescents (1978-1997): report from the Automated Childhood Cancer Information System project

Data on 1690 childhood and adolescent cases of thyroid cancer registered in 61 European cancer registries were extracted from the database of the Automated Childhood Cancer Information System (ACCIS) and included in analyses of incidence and survival. In 1988-1997, the age-standardised incidence rates (ASR) for children aged 0-14 years varied in European regions from 0.5 to 1.2 per million and the age-specific incidence in adolescents aged 15-19 years ranged from 4.4 to 11.0 per million. Over the age-span 0-19 years, the female to male ratio increased from 1 to around 3. Papillary thyroid cancer accounted for almost 65% of cases in children and 77% in adolescents. In the childhood population of Belarus, the ASR for 1989-1997 was 23.6 per million and the proportion of papillary tumours was 87%. No association was found between thyroid cancer risk and national dietary iodine status across 16 countries. Incidence of thyroid carcinoma among children and adolescents in Europe (excluding Belarus) increased during 1978-1997 by 3% per year, largely due to papillary carcinoma. Survival of children and adolescents was high over the entire study period and in all regions of Europe. Children with medullary carcinoma had slightly lower 5-year survival (95%, 95% CI 81-99), than those with papillary carcinoma (99%, 95% CI 95-100). More than 90% of patients survived 20 years after diagnosis. Further standardisation of diagnostic, classification and registration criteria will be fundamental for future studies of thyroid carcinomas in young people.

Thyroid disorders in employees of a nuclear power plant

BACKGROUND

The thyroid gland is a potential target organ for radiation-related damage. The aim of this analysis was to investigate the association between occupational exposure to ionizing radiation and the risk of autoimmune thyroid disease as well as thyroid nodules and dysfunction in workers of a former nuclear power station.

METHODS

Seventy-one male power station workers 38 to 57 years of age who had been exposed to a lifetime dose in the upper allowed range (accumulated lifetime dose 70 to 400 mSv) were compared to a population-based sample of 670 males who were not exposed to occupational radiation. Thyroid ultrasound was performed by the same observers. Laboratory parameters were analyzed in a central laboratory.

RESULTS

After controlling analyses for age and further relevant confounders no significant differences with respect to thyroid nodules and markers of autoimmune thyroid disease were detected between exposed and nonexposed individuals. However, nuclear power plant employees had higher odds for elevated serum thyrotropin (TSH) levels than the reference group (odds ratio 4.54; 95% confidence interval 1.43; 13.91).

CONCLUSIONS

Workers of a nuclear power plant with occupational exposure to ionizing radiation within the upper allowed dose range have an increased risk of elevated serum TSH levels. Further studies are required to confirm possible effects of occupational exposure to radiation on thyroid function.

Are possible risk factors for differentiated thyroid cancer of prognostic importance?

OBJECTIVE

The only established risk factor for differentiated thyroid cancer (DTC) is ionizing radiation. How ionizing radiation and other possible risk factors for DTC influence the prognosis has not extensively been investigated. We studied if factors such as smoking, number of children, previous thyroid disorders, previous radiotherapy toward the neck, family history of thyroid diseases, and malignancies influenced survival for patients with DTC.

DESIGN

A nested case-control study was conducted within the cohort of all patients diagnosed with DTC in Sweden between 1958-1987. Cases consisted of patients who died from DTC. One control, matched by age at diagnosis, gender, and calendar period was randomly selected from the risk set for each case. Information of risk factors was collected from the medical records. Associations between these factors and prognosis were assessed using conditional logistic regression.

MAIN OUTCOME

Smokers had a borderline significant increased risk of dying from DTC. Previous radiotherapy towards the neck region had no prognostic implication. A family history of DTC influenced prognosis although not significant due to few cases. The remaining risk factors studied did not influence survival.

CONCLUSIONS

In conclusion, smokers seemed to have a worsened prognosis compared to nonsmokers and a family history of thyroid cancer had a nonsignificant negative effect on survival.

Radiation-induced thyroid cancer: what we have learned from chernobyl

An increased incidence of thyroid cancer in the exposed children remains the most well-documented long-term effect of radioactive contamination after the Chernobyl nuclear accident in April, 1986. Multiple studies on approx 4000 children and adolescents with thyroid cancer have provided important new information about the epidemiological, clinical, pathological, and molecular aspects of radiation-induced carcinogenesis in the thyroid gland. They revealed that environmental exposure to 131I during childhood carries an increased risk of thyroid cancer and the risk is radiation dose dependent. The youngest children are most sensitive to radiation-induced carcinogenesis, and the minimal latent period for thyroid cancer development after exposure is as short as 4 yr. The vast majority of these cancers are papillary carcinomas, many of which have characteristic solid or solid-follicular microscopic appearance. On the molecular level, post-Chernobyl tumors are characterized by frequent occurrence of chromosomal rearrangements, such as RET/PTC, whereas point mutations of BRAF and other genes are much less common in this population.

Thyroid nodules and cancers in children

Thyroid nodules are clinically evident in approximately 1% of children and about 30% of these are malignant. In addition to requiring appropriate surgery, thyroid hormone replacement in and follow-up monitoring of patients who are members of families with tumor syndromes must be studied for other components of these syndromes.

Diagnosis of Thyroid Cancer in Children: Value of Gray-Scale and Power Doppler US

PURPOSE

To prospectively analyze the accuracy of various diagnostic criteria for cancer in solid thyroid nodules in children on the basis of gray-scale and power Doppler ultrasonographic (US) findings.

MATERIALS AND METHODS

The study protocol was approved by the institutional review board, and patient's parents gave full informed consent. One hundred three consecutive pediatric patients with solid thyroid nodules were included in the study. Thirty-five patients had thyroid cancer (mean age, 14.6 years +/- 2.6 [standard deviation]; range, 10-18 years), and 68 patients had benign thyroid nodules (mean age, 14.2 years +/- 2.9; range 9-18 years). Three-dimensional US was used to determine the volume of thyroid gland and thyroid nodules. Results of nodule cytologic and histologic examination and long-term clinical and US follow-up were used as a proof of final diagnosis. The following US characteristics were evaluated: location, echogenicity, echotexture, outline, presence of a halo, microcalcifications, and type of vascularization. Multivariate logistic regression analysis was used to evaluate the accuracy of US criteria for thyroid cancer in lesions with diameter of 15 mm and smaller and lesions with diameter larger than 15 mm. Qualitative variables were compared by using the chi(2) test and quantitative variables were compared by using the Student t test. Significance was defined at P < .05.

RESULTS

In thyroid nodules with diameter of 15 mm and smaller, the most reliable diagnostic criteria for malignancy were an irregular outline (sensitivity, 69.6%; specificity, 86.4%; P < .001), subcapsular location (sensitivity, 65.2%; specificity, 86.4%; P < .001), and increased intranodular vascularization (sensitivity, 69.6%; specificity, 87.9%; P < .01). For thyroid nodules larger than 15 mm in diameter, the accuracy of US diagnosis was much lower than that for smaller nodules. The only reliable criterion for cancer in this group was hypoechogenicity (sensitivity, 60.0%; specificity, 84.0%; P < .01).

CONCLUSION

Study findings indicate that US is most helpful in diagnosis of thyroid malignancy in thyroid nodules with diameter of 15 mm and smaller, with detection of irregular tumor outline, subcapsular location, and increased intranodular vascularization.

Follicular cell-derived thyroid cancer in children

Thyroid carcinoma is a rare disease in childhood. The only known causative factor is radiation exposure during childhood. Most cases can be cured by surgery and eventually radioiodine. The aim of initial treatment should be the total removal of neoplastic foci with a minimal morbidity. Some cancer-related deaths have been reported decades after initial treatment.

Follicular-cell derived thyroid cancer in children

Thyroid carcinoma is a rare disease in children, and is mostly of the papillary histological type. It is often extended at presentation with frequent lymph node metastases. Treatment includes surgery (total thyroidectomy and lymph node dissection) and radioiodine therapy in case of extensive disease. Life long thyroxine treatment is given to all patients and when carefully controlled is devoided of adverse effects. Long term prognosis is favorable, but a few deaths have been reported some decades after initial treatment. Adverse prognostic indicators are younger age at discovery and presence of distant metastases.

Role of neck ultrasonography in the follow-up of children operated on for thyroid papillary cancer

The aim of this study was to evaluate the role of neck ultrasonography compared to (131)I whole-body scan (WBS) and circulating thyroglobulin (Tg) measurement after thyroid hormone withdrawal in the follow-up of children with thyroid papillary cancer, who had previously undergone total thyroidectomy for the diagnosis of neck lymph node metastases (LNM). Forty-five children were examined. Neck ultrasonography and diagnostic WBS were conclusive about the presence or absence of LNM in 35 patients. Diagnostic WBS revealed the presence of LNM in 6 cases not detected by neck ultrasonography; neck ultrasonography was positive in 3 cases that were negative at diagnostic WBS but confirmed by post-(131)I therapy WBS. One patient with suspicious neck lymphnodes at neck ultrasonography not confirmed by WBS was considered as a false-positive result of neck ultrasonography. Neck ultrasonography and thyroglobulin (Tg) were conclusive about the presence or absence of LNM in 29 patients. Tg was elevated in 10 subjects with negative neck ultrasonography (7 had also lung and/or mediastinic LNM). Tg was undetectable in 5 patients in whom the presence of LNM was confirmed by neck ultrasonography and WBS. In conclusion, our study in children demonstrates that neck ultrasonography can detect LNM that are not suspected by palpation, diagnostic WBS, or serum Tg determination. Furthermore, neck ultrasonography can pinpoint the anatomic site of the LNM.

Thyroid neoplasia following irradiation in adolescent and young adult survivors of childhood cancer

OBJECTIVES

To describe a cohort of survivors of childhood malignancy at risk of developing thyroid abnormality, and propose guidelines for management of such patients.

DESIGN

Retrospective case series.

SETTING

Late-effects oncology clinic at a large children's hospital in Sydney.

SUBJECTS

142 patients who had received irradiation to the thyroid from the 1970s onwards, who attended the late-effects clinic from May 1989 to December 1998.

INTERVENTIONS

Thyroid palpation by an endocrinologist or surgeon, serum thyroid-stimulating hormone assay and thyroid ultrasound examination were performed on all subjects and, depending on findings, some subjects proceeded to fine-needle biopsy or surgery (total thyroidectomy). A few patients required adjuvant (131)I administration.

OUTCOME MEASURES

Radiation dose received; results of thyroid palpation; thyroid function tests; ultrasound findings; diagnosis of the abnormalities; and outcomes of surgical interventions.

RESULTS

49 subjects (24 of 65 patients who received scatter irradiation to the thyroid and 25 of 78 patients who received direct irradiation) had thyroid surgery. Of these, 12 in the scatter and six in the direct irradiation group were found to have thyroid malignancy. Fifty subjects with abnormal ultrasound results remain under surveillance. Having a palpable thyroid was predictive of malignancy, but age at original diagnosis, sex, current age, time since irradiation, radiation dose, nodule type and nodal involvement were not.

CONCLUSION

There is a significant risk of cancer in thyroid glands exposed to radiation as part of therapy for childhood cancer. This risk is greater for patients who received scatter (versus direct) irradiation. Nodular change is usually not apparent for many years, so lifelong surveillance is necessary. Palpation alone is not sufficient to detect thyroid cancer and thyroid ultrasound examination is recommended.

The epidemiology and etiology of differentiated thyroid carcinoma

Differentiated thyroid carcinoma (DTC) is a rare tumor with a relatively good prognosis, but in about 10% of cases it may be the cause of death. Papillary carcinoma is more frequent (about 70-80% of cases) and less aggressive than follicular cancer: the papillary/follicular ratio is increased in areas of high iodine intake. In recent years many genes have been found to be mutated in DTC, the most important of these being ras, ret, trk, and met. The relationship between radiation exposure and DTC is well recognized, especially in children. Since the Chernobyl nuclear accident, a high incidence of DTC has been found in children exposed to fallout.

Molecular alterations involving p53 codons 167 and 183 in papillary thyroid carcinomas from chernobyl-contaminated regions of belarus

After the Chernobyl accident in 1986, there was a significant increase in the incidence of papillary thyroid carcinoma in fallout-exposed children from Belarus. We studied the p53 gene from 24 papillary thyroid carcinoma cases presenting in 1996. All subjects lived in contaminated regions of Belarus at the time of the accident and were under age 20 when exposed to fallout. Exons 5 through 9 of p53 were amplified from genomic tumor DNA using the polymerase chain reaction (PCR). The PCR products were analyzed by direct DNA sequencing using an automated sequencer. Five cases each exhibited two molecular alterations within exon 5. Alterations were confirmed by sequencing in both directions. One alteration, involving codon 167 (CAG-->CAT) in all five cases, resulted in the substitution of HIS for GLN. The second alteration, involving codon 183 (TCA-->TGA) in all five cases, resulted in a premature termination codon. Leukocyte DNA from each of the positive cases was analyzed and found to contain only wild-type p53 sequence. These results suggest that mutations involving codons 167 and 183 in the p53 locus are important in the pathogenesis of a subset (21%) of radiation-induced papillary thyroid carcinomas from Belarus.

Thyroid consequences of the Chernobyl nuclear accident

It is well recognized that the use of external irradiation of the head and neck to treat patients with various non-thyroid disorders increases their risk of developing papillary thyroid carcinoma years after radiation exposure. An increased risk of thyroid cancer has also been reported in survivors of the atomic bombs in Japan, as well as in Marshall Island residents exposed to radiation during the testing of hydrogen bombs. More recently, exposure to radioactive fallout as a result of the Chernobyl nuclear reactor accident has clearly caused an enormous increase in the incidence of childhood thyroid carcinoma in Belarus, Ukraine, and, to a lesser extent, in the Russian Federation, starting in 1990. When clinical and epidemiological features of thyroid carcinomas diagnosed in Belarus after the Chernobyl accident are compared with those of naturally occurring thyroid carcinomas in patients of the same age group in Italy and France, it becomes apparent that the post-Chernobyl thyroid carcinomas were much less influenced by gender, virtually always papillary (solid and follicular variants), more aggressive at presentation and more frequently associated with thyroid autoimmunity. Gene mutations involving the RET proto-oncogene, and less frequently TRK, have been shown to be causative events specific for papillary cancer. RET activation was found in nearly 70% of the patients who developed papillary thyroid carcinomas following the Chernobyl accident. In addition to thyroid cancer, radiation-induced thyroid diseases include benign thyroid nodules, hypothyroidism and autoimmune thyroiditis, with or without thyroid insufficiency, as observed in populations after environmental exposure to radioisotopes of iodine and in the survivors of atomic bomb explosions. On this basis, the authors evaluated thyroid autoimmune phenomena in normal children exposed to radiation after the Chernobyl accident. The results demonstrated an increased prevalence of circulating thyroid antibodies not associated with significant thyroid dysfunction. This finding is consistent with the short period of follow-up, but it is highly likely that these children will develop clinical thyroid autoimmune diseases in the future. Therefore, screening programmes for this at-risk population should focus, not only on the detection of thyroid nodules and cancer, but also on the development of thyroid autoimmune diseases.

Post-Chernobyl increased prevalence of humoral thyroid autoimmunity in children and adolescents from a moderately iodine-deficient area in Russia

Circulating thyroglobulin antibodies (TgAb) and thyroperoxidase antibodies (TPOAb) were measured in 143 iodine-deficient children, 5 to 15 years of age, from the Region of Tula, Russia, who had been moderately contaminated after the Chernobyl disaster (37-185 GBq/km2 of caesium-137, [group A]) and in 40 sex- and age-matched subjects from an uncontaminated neighboring area (<3.7 GBq/km2 of caesium-137, [group B]). Increased thyroid size at sonography was found in 41% and in 45% subjects from group A and group B, respectively, associated with supranormal thyrotropin (TSH) values in 7.7% of group A and 7.5% of group B, without differences in average serum free thyroxine (FT4), free triiodothyronine (FT3) and TSH. Serum thyroperoxidase antibody (TPOAb)-associated or not with thyroglobulin-antibody (TgAb) as detected in 18.9% of children and adolescents from group A, about four-fold higher than in group B (5%, Fischer's exact test p<0.05). A 24% frequency was found in subjects whose age, at the moment of the disaster was 0-72 months or were in utero, but the frequency was about 7%, similar to that in group B, in those who had not yet been conceived at that time. Less than half of antibody-positive group A children were hyperthyrotropinemic, whereas no group B subclinical hypothyroid subject was antibody-positive, thus excluding the autoimmune etiology of the subclinical thyroid failure; more likely it is attributable to iodine malnutrition. The high prevalence of humoral thyroid autoimmunity phenomena in the investigated area suggests a combined role of iodine malnutrition in enhancing the effects of short lived iodine isotopes, particularly evident in pubertal individuals conceived or born immediately before the Chernobyl disaster.

Molecular genetics of childhood papillary thyroid carcinomas after irradiation: high prevalence of RET rearrangement

Epidemiological studies have revealed a connection between thyroid carcinogenesis and a history of radiation. The molecular mechanisms involved are not well understood. It has been claimed that RAS, p53 or GSP mutations and RET or TRK rearrangements might play a role in adult thyroid tumors. In childhood, the thyroid gland is particularly sensitive to ionizing radiation. The reactor accident in Chernobyl provided a unique chance to study molecular genetic aberrations in a cohort of children who developed papillary thyroid carcinomas after a short latency time after exposure to high doses of radioactive iodine isotopes. According to the concepts of molecular genetic epidemiology, exposure to a specific type of irradiation might result in a typical molecular lesion. Childhood papillary thyroid tumors after Chernobyl exhibit a high prevalence of RET rearrangement as almost the only molecular alteration. The majority showed RET/PTC3 (i.e., ELE/RET rearrangements), including several subtypes. Less frequently, RET/PTC1 (i.e., H4/RET rearrangements), and a novel type (RET/PTC5, i.e., RFG5/RET) were observed. Proof of reciprocal transcripts suggests that a balanced intrachromosomal inversion leads to this rearrangement. Breakpoint analyses revealed short homologous nucleotide stretches at the fusion points. In all types of rearrangement, the RET tyrosine kinase domain becomes controlled by 5' fused regulatory sequences of ubiquitously expressed genes that display coiled-coil regions with dimerization potential. Oncogenic activation of RET is apparently due to ligand-independent constitutive ectopic RET tyrosine kinase activity. The analysis of this cohort of children with radiation-induced thyroid tumors after Chernobyl provides insights into typical molecular aberrations in relation to a specific mode of environmental exposure and may serve as a paradigm for molecular genetic epidemiology.

Low prevalence of the ret/PTC3r1 rearrangement in a series of papillary thyroid carcinomas presenting in Belarus ten years post-Chernobyl

After the Chernobyl accident in 1986, there was a significant increase in the incidence of papillary thyroid cancer in fallout-exposed children from Belarus. Radiation-induced rearrangements of chromosome 10 involving the c-ret proto-oncogene have been implicated in the pathogenesis of these cancers. The ret/PTC3r1 rearrangement was the most prevalent molecular lesion identified in post-Chernobyl papillary thyroid cancers arising in 1991 and 1992. We identified the ret/PTC1 rearrangement in 29% of 31 papillary thyroid cancers presenting in Belarus in 1996. In the present report, we examined 14 cases from this series (plus 1 additional case) and found a ret/PTC3r1 rearrangement in only 1 (7%). The prevalence of ret/PTC3r1 in this series is significantly lower than previously reported (p = 0.0006, Fisher exact test). This result suggests a switch in the ratio of ret/PTC3 to ret/PTC1 rearrangements in late (1996) versus early (1991-1992) post-Chernobyl papillary thyroid cancers.