Dynamics of thyroid cancer incidence in Russia following the Chernobyl accident

Thyroid cancer overdiagnosis revisited

BACKGROUND

Evidence has accumulated showing that an increase in thyroid cancer incidence reflects overdiagnosis of clinically unimportant lesions due to the rise in the use of neck ultrasonography. In the manuscript we examine the hypothesis that the rise in thyroid cancer incidence in Russia is largely caused by overdiagnosis.

MATERIALS AND METHODS

Incidence and mortality rates of thyroid cancer for Russia overall and its administrative regions were abstracted from the statistical database of the Ministry of Health of Russia. For incidence trends, we calculated the percentage change, linear regression coefficient and p-value. The calculation of excess cases was based on expected age-specific distributions assuming that the incidence of thyroid cancer increases exponentially with age, as predicted by the multistage model of carcinogenesis.

FINDINGS

Over the study period (1989-2015) the age standardized incidence of thyroid cancer has tripled in Russian women and doubled in men. Strong support for the hypothesis that the increase in thyroid cancer incidence may be artificial is evident from age-specific incidence trends: increases in incidence in middle age but not in older ages, thereby altering the age curves from the expected exponential shape to an "inverted U" shape. The number of observed cases of thyroid cancer exceeded the expected number by 138, 325 or 70 % of all cases diagnosed with thyroid cancer. We attribute the excess cases to detection by ultrasonography clinically unimportant lesions. This is supported by a very high incidence -to-mortality ratio, low case fatality, high and growing prevalence of thyroid cancer.

CONCLUSION

Although there is an evidence that exposure to iodine 131 (¹³¹I) is an important cause of the increase in incidence of thyroid cancer in high-risk populations, we have shown that this increase could largely be attributed to overdiagnosis associated with ultrasonography screening. Overdiagnosis is the only explanation of the increase in thyroid cancer incidence in low-risk regions.

Radiation accidents over the last 60 years

Since the end of the Second World War, industrial and medical uses of radiation have been considerably increasing. Accidental overexposures of persons, in either the occupational or public field, have caused deaths and severe injuries and complications. The rate of severe accidents seems to increase with time, especially those involving the public; in addition, accidents are often not immediately recognised, which means that the real number of events remains unknown. Human factors, as well as the lack of elementary rules in the domains of radiological safety and protection, such as inadequate training, play a major role in the occurrence of the accidents which have been reported in the industrial, medical and military arenas.

Chronic contamination of rats with 137 cesium radionuclide: impact on the cardiovascular system

Cardiovascular system impairment has been observed in children and in liquidators exposed to the Chernobyl nuclear power plant accident. No experimental studies of animals have analyzed whether these disorders might be attributed to chronic ingestion of low levels of cesium 137 ((137)Cs). Biochemical, physiological, and molecular markers of the cardiovascular system were analyzed in rats exposed through drinking water to (137)Cs at a dose of 500 Bq kg(-1) (6500 Bq l(-1)). Plasma concentrations of CK and CK-MB were higher (+52%, P < 0.05) in contaminated rats. No histological alteration of the heart was observed, but gene expression was modified in the atria. Specifically, levels of ACE (angiotensin converting enzyme) and BNP (brain natriuretic peptide) gene expression increased significantly (P < 0.05). ECG analysis did not disclose any arrhythmia except ST- and RT-segment shortening (-9% and -11%, respectively, P < 0.05) in rats exposed to (137)Cs. Mean blood pressure decreased (-10%, P < 0.05), and its circadian rhythm disappeared. Overall, chronic contamination by an extreme environmental dose of (137)Cs for 3 months did not result in cardiac morphological changes, but the cardiovascular system impairments we observed could develop into more significant changes in sensitive animals or after longer contamination.

Thyroid cancer incidence among people living in areas contaminated by radiation from the Chernobyl accident

As a result of the Chernobyl nuclear power plant accident, massive amounts of radioactive materials were released into the environment and large numbers of individuals living in Belarus, Russia, and Ukraine were exposed to radioactive iodines, primarily 131I. Iodine-131 concentrated in the thyroid gland of residents of the contaminated areas, with children and adolescents being particularly affected. In the decade after the accident, a substantial increase in thyroid cancer incidence was observed among exposed children in the three affected countries, and compelling evidence of an association between pediatric thyroid cancer incidence and radiation exposure to the thyroid gland accumulated. The data currently available suggest that both the magnitude and patterns of thyroid cancer risk are generally consistent with those reported following external exposure. Based on data from case-control studies, iodine deficiency appeared to enhance the risk of developing thyroid cancer following exposure from Chernobyl. Results from a recent large cohort study, however, did not support these findings. Data on adult exposure are limited and not entirely consistent. Similarly, information on thyroid cancer risks associated with in utero exposure is insufficient to draw conclusions. The lack of information on these two population groups indicates an important gap that needs to be filled. Twenty years after the accident, excess thyroid cancers are still occurring among persons exposed as children or adolescents, and, if external radiation can be used as a guide, we can expect an excess of radiation-associated thyroid cancers for several more decades. Since considerable uncertainties about the long-term health effects from Chernobyl remain, continued follow-up of the exposed populations should provide valuable information.

No increase in thyroid cancer among children and adolescents in Finland due to Chernobyl accident

The aim of the study was to assess whether radioactive fallout from the Chernobyl accident in 1986 influenced thyroid cancer incidence among children and adolescents in Finland. The population was divided into two: those with thyroid doses less than 0 6 mSv and above 0.6 mSv. Cumulative incidence of thyroid cancer was identified from the Finnish Cancer Registry from a population aged 0-20 years in 1986 with a total of 1,356,801 persons. No clear difference in underlying thyroid cancer incidences rates were found during the pre-Chernobyl period (1970-1985) (rate ratio RR 0.95, 95% confidence interval CI 0.81-1.10). During the post-Chernobyl period (1991-2003), thyroid cancer incidence was lower in the more exposed population than in the less exposed population (RR 0.76, 95% CI 0.59-0.98). Our results did not indicate any increase in thyroid cancer incidence related to exposure to radiation from the Chernobyl accident.

Radiation-epidemiological studies of thyroid cancer incidence among children and adolescents in the Bryansk oblast of Russia after the Chernobyl accident (1991-2001 follow-up period)

In this study, thyroid cancer incidence (follow-up period: 1991-2001) has been analyzed, including persons who were exposed as children at an age between 0 and 17 years and who are living in the Bryansk oblast, the worst contaminated area of Russia after the Chernobyl accident. According to the census of 1989, the population of this oblast comprises 375 thousand people. Thyroid doses from incorporated radioiodine isotopes -- both for the thyroid cancer cases and the study population -- were determined based on the official methodology approved by the Russian Scientific Commission on Radiation Protection. Between 1991 and 2001, a total of 199 thyroid cancer cases were diagnosed at cancer centers (the so-called oncological dispensaries) of the investigated regions. The performed analysis relies on medical and dosimetric information available from the Russian National Medical and Dosimetric Registry which was established after the Chernobyl accident. Diagnoses were confirmed histologically for 95% of the cases. The analysis described revealed statistically significant radiation risk only for those exposed as children at an age of 0-9 years. In this group, the standardized incidence ratio (the national incidence rate was used as a reference) in the considered time period is estimated to be 6.7 (5.1, 8.6 95%CI) and 14.6 (10.3, 20.2 95%CI) for girls and boys, respectively. The risk dependence on age at exposure has also been studied. It has been shown that the smaller the age the higher the risk. For girls whose age at exposure was 0-4 years, the excess relative risk per 1 Gy for the period 1991-2001 was 45.3 (5.2, 9,953 95%CI; with internal control) and 28.8 (4.3, 2,238 95%CI; with external control), respectively. For boys whose age at exposure was 0-9 years the corresponding excess relative risk per 1 Gy was 68.6 (10.0, 4,520 95%CI) and 177.4 (-276, 10(6) 95%CI), respectively. Dependence of radiation risk on time was studied, with the focus on two follow-up periods 1991-1996 and 1997-2001, respectively. In 1997-2001 the radiation risk is shown to decrease among girls, and increase among boys.

Post-Chornobyl Thyroid Cancers in Ukraine. Report 1: Estimation of Thyroid Doses

About 1.8 EBq of 131I was released into the atmosphere during the Chornobyl accident that occurred in Ukraine on April 26, 1986. More than 10% of this activity was deposited on the territory of Ukraine. Beginning 4-5 years after the accident, an increase in the incidence of thyroid cancer among children, believed to be caused in part by exposure to 131I, has been observed in different regions of Ukraine. A three-level system of thyroid dose estimation was developed for the reconstruction of thyroid doses from 131I for the entire population of Ukrainian children aged 1 to 18 at the time of accident: (1) At the first level, individual doses were estimated for the approximately 99,000 children and adolescents with direct measurements of radioactivity in the thyroid (so-called direct thyroid measurements) performed in May-June of 1986; (2) at the second level, group doses by year of age and by gender were estimated for the population of 748 localities (with 208,400 children aged 1-18 in 1986) where direct thyroid measurements of good quality were performed on some of the residents; and (3) at the third level, group doses by age and by gender were estimated for the population of the localities where no thyroid measurements were made in 1986. The third-level doses were then aggregated over the population of each oblast. Data, models and procedures required for each level of thyroid dose estimation are described in the paper. At the first level, individual doses were found to range up to 27,000 mGy, with geometric and arithmetic means of 100 and 300 mGy, respectively. At the second level, group doses were found to be highest for the younger children (aged 1 to 4 years); doses for the older children (aged 16 to 18 years) were 3.5 times smaller. At the third level, average population-weighted doses were found to exceed 35 mGy in the five northern oblasts closer to the Chornobyl reactor site; to be in the 14- to 34-mGy range in seven other oblasts, Kyiv city and Crimea; and to be less than 13 mGy in all other oblasts.

Non-cancer thyroid diseases among children in the Kaluga and Bryansk regions of the Russian Federation exposed to radiation following the Chernobyl accident

This paper presents results of estimated radiation risks of non-cancer thyroid diseases in the people from Kaluga and Bryansk regions of the Russian Federation exposed in their childhood to radioiodine as a result of the Chernobyl accident. This work was carried out under the Joint Medical Research Project on non-cancer thyroid diseases conducted by Sasakawa Memorial Health Foundation and the Medical Radiological Research Center of the Russian Academy of Medical Sciences. The subjects were 2,457 people who underwent health examinations from 1997 to the end of 1999 who had individual radiometric thyroid data obtained between May and June 1986 and were aged 10 y or less at the time of exposure. The thyroid absorbed doses from incorporated 131I were estimated on the basis of measurements of exposure dose rate in the vicinity of the subject's thyroid and liver. A compartment model accounting for 131I metabolism in humans and cows was used. The estimated dose varied from 0 to 6 Gy, and its distribution was approximately lognormal with a mean of 0.132 Gy and standard deviation of 0.45 Gy. The prevalence of diffuse goiter in males showed a significant dose-response (p = 0.03) with an estimated odds ratio 1.36 at 1 Gy.

Histological validation of diagnoses of thyroid cancer among adults in the registries of Belarus and the Ukraine

In order to evaluate the diagnostic reliability of the thyroid cancers listed in adult registries from the Ukraine and Belarus, a histological review was organised of 327 randomly selected thyroid carcinoma cases diagnosed between 1980 and 1999. A final diagnosis was reached at a 5-day consensus conference by six pathologists who met around a multiheaded microscope. The study concluded with a comparison between the final diagnosis and the initial diagnosis. The pathologists agreed with the initial diagnosis of malignancy in 286 cases (88%). A final diagnosis of papillary, follicular or medullary thyroid carcinoma was reached in 86, 4, and 6% of the cases respectively. In 2.8% of the cases reviewed, diagnostic discrepancies persisted. The percentage of agreement between the final diagnosis and the initial diagnosis was 93%, with a weighted κ-statistic of 0.61 (confidence interval 95% (CI_95%): [0.45–0.77]). In all, 89% of the 286 confirmed cancer cases were in agreement for the type of cancer, with a κ-statistic of 0.56 (CI_95%: [0.43–0.69]). The level of agreement differed according to cancer categories, with concordance rates of 94, 40 and 33% for papillary, follicular and medullary thyroid carcinomas respectively. The low prevalence of follicular thyroid carcinomas in the adult population studied calls for further exploration. The discrepancies and classification difficulties encountered were analysed.

Enhancing Nuclear Emergency Preparedness

On January 31, 2002, Vermont's health commissioner requested potassium iodide (KI) for individuals in the 10-mile Emergency Planning Zone of the nuclear power facility. Vermont's KI distribution program emphasized public information about the role, risks, and benefits of KI. Predistribution ensured that individuals could receive KI in a 0- to 4-hour time period, to provide maximum protection. Five months after the program began, more than 1,000 individuals had received KI, and 3,000-4,000 KI doses have been distributed in schools. Efforts are ongoing to identify barriers to participation, provide public education, and evaluate KI distribution efforts.

A report of six cases of familial papillary thyroid cancer

AIMS

Familial occurrence of papillary thyroid cancer is uncommon. The purpose of this study was review our own experience in a series of 267 papillary thyroid cancers.

METHODS

We analysed the clinical records of 267 consecutive patients operated on for papillary thyroid cancer (PTC) in our hospital between June 1980-March 2000.

RESULTS

We identified a family history in three families (6 patients), which results in a 2.25% familial papillary thyroid carcinoma (FPTC) rate. Pathology findings revealed that the tumour was multifocal and bilateral in 2 patients. Lymph-node metastases were found in 4 patients. They are all alive with a mean time of follow-up of 74.3 months (range 2-120).

CONCLUSIONS

We recommend that patients with familial disease should be treated according to the disease stage and other risk factors, similar to those with sporadic differentiated papillary thyroid cancer. We encourage the further reporting and pedigree analysis to identify patients affected by FPTC.

Thyroid cancer incidence among adolescents and adults in the Bryansk region of Russia following the Chernobyl accident

Thyroid cancer incidence in the Bryansk region, the most contaminated area of Russia after the Chernobyl accident, is analyzed for the residents aged 15-69 y at the time of the accident (about 1 million persons according to the 1989 census) for the period from 1986 to 1998. Sex and age standardized incidence rates are presented and compared to the whole Russian population rates (SIR analysis). Also, a geographical correlation analysis is performed for incidence rates and mean thyroid doses at the district level, which provides a basis for preliminary estimation of radiation associated risks for the period 1991-1998 (to allow for a potential five year latent period). Thyroid doses were estimated based on the State official document "Methodology for reconstruction of dose from iodine radioisotopes in residents of the Russian Federation exposed to radioactive contamination as a result of the Chernobyl accident in 1986" (2000). Altogether, 1,051 thyroid cancer cases were detected in the Bryansk oncological dispensary from 1986 to 1998 and 769 from 1991 to 1998. Histological confirmation was available for 87% and 95% of these cases, respectively. Standardized incidence ratios (SIR) were 1.27 (95% CI = 0.92, 1.73) for the period 1986-1990 and 1.45 (95% CI = 1.20, 1.73) for the period 1991-1998 for males and 1.94 (95% CI = 1.70, 2.20) and 1.96 (95% CI = 1.82, 2.1) for females. The excess relative risk per 1 Gy (using external control) estimate for the period 1991-1998 was -0.4 (95% CI = -3.5, 2.7), -1.3 (95% CI = -2.8, 0.1) for males and females, respectively, and -0.6 (95% CI = -2.1, 0.8) for both sexes. Using internal controls, the excess relative risk (ERR(1Gy)) per unit dose of 1 Gy was found to be 0.7 with 95% CI (-2.3, 5.2) for males, -0.9 with 95% CI (-2.4, 0.8) for females and 0.0 with 95% CI (-1.4, 1.7) for males and females together. These results are discussed in the light of the quality of information available on thyroid cancer cases and screening campaigns carried out after the Chernobyl accident.

Epidemiology of cancer in adolescents

In western populations, the annual incidence rate of cancer among adolescents aged 15-19 years is around 150-200 per million, intermediate between the rates for older children and young adults. The most frequent diagnostic groups are acute leukemia, lymphomas, central nervous system tumors, bone and soft tissue sarcomas, germ cell tumors, thyroid carcinoma, and malignant melanoma. While the causes of most cancers in teenagers are still unknown, health education and promotion and public health programs offer some scope for prevention among people of this age group. Reduction in sun exposure should lead to a reduction in incidence of melanoma, and elimination of hepatitis B in regions where it is endemic should result in a decrease in hepatic carcinoma. Five-year survival of patients diagnosed around 1990 exceeded 70% in the USA and UK. Entry to clinical trials appears to be much less frequent for adolescents with cancer than for children. There is some evidence that higher survival is associated with entry to trials or centralized treatment for certain cancers in this age group.

Chernobyl-related ionising radiation exposure and cancer risk: an epidemiological review

The Chernobyl nuclear accident on 26th April, 1986, led to a massive release of radionuclides into the environment. Although vast areas of Europe were affected by Chernobyl-related ionising radiation, the accident had the greatest impact in Belarus, Ukraine, and the Russian Federation. Epidemiological studies that have investigated the link between the Chernobyl accident and cancer have largely focused on malignant diseases in children, specifically thyroid cancer and leukaemia. There is good evidence to suggest that rates of thyroid cancer in children from the countries that were formally part of the Soviet Union have risen as a consequence of the Chernobyl accident. The findings for childhood leukaemia are less conclusive. Overall rates for this disease do not seem to have been affected by the Chernobyl-related ionising radiation, but there may be a larger risk of infant leukaemia in contaminated areas of Europe. Among adult populations, there is no strong evidence to suggest that risk of thyroid cancer, leukaemia, or other malignant disease has increased as a result of the Chernobyl accident.

Thyroid cancer after diagnostic administration of iodine-131 in childhood

Hahn, K., Schnell-Inderst, P., Grosche, B. and Holm, L-E. Thyroid Cancer after Diagnostic Administration of Iodine-131 in Childhood. Radiat. Res. 156, 61-70 (2001). To determine the carcinogenic effects of diagnostic amounts of (131)I on the juvenile thyroid gland, a multicenter retrospective cohort study was conducted on 4,973 subjects who either had been referred for diagnostic tests using uptake of (131)I (n = 2,262) or had had a diagnostic procedure on the thyroid without (131)I (n = 2,711) before the age of 18 years. Follow-up examinations were conducted after a mean period of 20 years after the first examination in 35% of the exposed subjects (n = 789) and in 41% of the nonexposed subjects (n = 1,118). Iodine-131 dosimetry of the thyroid was carried out according to ICRP Report No 53, and the median thyroid dose was 1.0 Gy. In the exposed group, two thyroid cancers were found during 16,500 person-years, compared to three cancers in the nonexposed group during 21,000 person-years. The relative risk for the exposed group was 0.86 (95% CI: 0.14-5.13). The study did not demonstrate an increased risk for thyroid cancer after administration of (131)I in childhood.