THYROID CANCER INCIDENCE IN THE POPULATION OF UKRAINE AND ITS EPIDEMIOLOGICAL DETERMINANTS: IONIZING RADIATION AND ENDOCRINE DISRUPTORS

OBJECTIVE

to estimate the risk of thyroid cancer incidence in the population of Ukraine in connection with its exposure to radioactive iodine fallout of Chornobyl origin and the use of pesticides in agricultural production in the country.

OBJECT OF STUDY

Incidence rates of thyroid cancer in the population of Ukraine in 2001-2019, average regional radiation doses absorbed by the thyroid because of the Chornobyl accident, the volume of use of various groups of pesticides in the regions of Ukraine.

RESEARCH METHODS

statistical, mathematical and cartographic.

RESULTS

The study covering the period of 2001-2019, revealed significant temporal and regional differences in the thyroid cancer incidence in the population of the Ukraine regions in 2001-2019. The existence of a significant correlation between the thyroid cancer incidence and the amount of radiation exposure to the thyroid associated with the Chornobyl accident was established. The existence of a significant correlation between the thyroid cancer incidence and the degree of pesticide use intensity in agriculture in the Ukraine regions was established. A significant value of multiple correlation r = 0.5866 (p < 0.05) was found between the thyroid cancer incidence in Ukraine andthe average regional radiation doses and the pesticide use intensity in agricultural production in the country.

CONCLUSIONS

A reliable value of the multiple correlation between the value of the average regional radiation exposure doses to the thyroid associated with the Chornobyl accident and the degree of pesticide use intensity in the national economy of Ukraine and the thyroid cancer incidence in the population was determined.

LATE ONCOLOGICAL AFTEREFFECTS OF RADIATION EXPOSURE CAUSED BY THE CHORNOBYL ACCIDENT

Studies of the longterm oncological consequences after the Chornobyl accident show a significant impact of radiation exposure on the cancer incidence rate in affected population in Ukraine. This is supported by the increased radiation risk of leukaemia in liquidators, which exceeds national population rates, and its value is comparable to the data on hibakushi, who were subjected to Abombings. For the first time in the cleanup workers cohort the radiation dependence of chronic lymphoid leukaemia was established. There are radiation associated risks of leukemia in children who have been exposed to radiation from the Chornobyl accident. There has been registered an increase of thyroid cancer incidence in children and adults (liquidators, evacuees from the 30km exclusion zone and residents of the most contaminated territories). There is an excess of breast cancer in female liquidators. The frequency of all forms of malignant neoplasms decreases over time but still exceeds national rates. Further monitoring of malignant neoplasms in the groups of affected population will allow evaluating the radiation risks of cancer forms whose radiationassociated manifestation is already known from previous studies or can be expected in the future.

INCIDENCE OF MALIGNANT NEOPLASMS AMONG RESIDENTS OF SMALL RADIONUCLIDE-CONTAMINATED CHORNOBYL DISTRICTS IN A POST-ACCIDENT PERIOD

OBJECTIVE

To assess the level of risks of development of malignant neoplasms among the residents of smallChornobyl districts («rayons») in connection with low-dose radiation exposure and its dynamic changes.

MATERIALS AND METHODS

The study population included residents of Borodianka, Ivankiv and Poliske districts ofKyiv region («oblast») and Luhyny, Narodychi and Ovruch districts of Zhytomyr region, 175,100 inhabitants in2017. The study period was 1980-2017. All cancers incidence rates as well as rates of potentially radiation-associated sites (breast, thyroid, hematopoietic and lymphoid systems) were calculated and analysed. Methods of variation statistics, descriptive and analytical epidemiology were used.

RESULTS

The impact of ionizing radiation on population of the most radionuclide-contaminated districts raisesconcerns of the potential threat of adverse cancer effects, especially thyroid cancer. The average total whole-bodyeffective radiation doses received due to cesium during long time (1986-2005) among residents of the study districts (7.6-45.8 mSv) exceeded that in Zhytomyr (5.9 mSv), Kyiv (4.9 mSv) regions and Ukraine as a whole (2.48mSv), but also in other districts in the North Ukraine. The average doses of internal radiation absorbed by the thyroid gland (161-1559 mGy) among the most vulnerable population - children and adolescents (aged 0-18 yearsat the time of the accident) of these areas, and obtained in the short post-accident period, significantly exceedthat in Zhytomyr (87 mGy), Kyiv (81 mGy) regions and Ukraine as a whole (19 mGy). Irradiation rates of adult residents of these territories were lower, but significantly exceeded the average doses received by the population ofUkraine and large administrative units. Overall cancer incidence in the 6 districts during pre- and post-accidentperiods was lower comparing to Ukraine's and Kyiv region's rates, and did not significantly differ from Zhytomyrregion's rates. At the same time, the incidence rates of thyroid cancer significantly exceeded that of the pre-accident period as well as Zhytomyr region's rates.

CONCLUSIONS

The results of the study indicate needs for further monitoring of malignant neoplasms not only inthe population of Ukraine as a whole and its large administrative-territorial units, but also among residents of particular areas, given the likelihood of the realization of the risks of radiation-associated diseases in the distantpost-accident period in accordance with local environmental conditions.

EPIDEMIOLOGY OF BREAST CANCER IN UKRAINE WITH CONSIDERATION OF THE FACTORS OF THE CHORNOBYL ACCIDENT

OBJECTIVE

Assessment of the possible impact of the Chornobyl accident on the incidence of breast cancer in the female population of Ukraine as a whole and in some affected groups.

OBJECT OF THE STUDY

The female population of Ukraine as a whole and in separate groups of victims - women par- ticipating in the clean-up works in 1986-1987, evacuaees from the exclusion zone and inhabitants of the territo- ries most contaminated with radionuclides.

METHODS

Statistical, mathematical, cartographic.

RESULTS

This study, covering a significant period of time (1976-2016), revealed a steady temporal and territorial agglomeration of regions with a higher incidence of breast cancer in the southern and south-eastern regions of Ukraine. Lower - in the western and northern regions. There is a steady increase in the incidence rate, but in recent years this growth has slowed down. The epidemiological situation regarding the incidence of breast cancer in the female population of Ukraine during the 30 years after the Chornobyl accident is generally stable. At the same time, a marked increase in the frequency of this pathology in the groups of the affected population, especially in women, participated in clean-up works in 1986-1987.

CONCLUSIONS

A stable agglomeration of regions with high levels of incidence in the south and south-east, and low in the west and north of the country is determined. The dynamics of breast cancer in Ukraine as a whole is characterized by steady growth, although in recent years its pace has slightly decreased. Among the individual population groups affected by the Chornobyl catastrophe (female liquidators, evacuated women from the exclusion zone, residents of the most contaminated with radionuclides territories) only among female liquidators of 1986-1987 the significant in- crease was observed in the incidence of breast cancer, which exceeds the national indicators at 1.3-1.6 times.

RADIATION RISKS OF THYROID CANCER IN CHORNOBYL CLEAN-UP WORKERS USING THE ALTERNATIVE ESTIMATES OF DOSES OF EXTERNAL EXPOSURE

OBJECTIVE

The objective of this study was to estimate the thyroid cancer radiation risks - excess absolute risk(EAR), excess relative risk (ERR) and attributable fraction of risk (AR) in the cohort of 150,813 Ukrainian male clean-up workers during the 1986-2012 period (more than 25 years after the Chornobyl accident).

MATERIALS AND METHODS

The cohort under study of 150,813 Ukrainian men who participated emergency and clean-up work in 1986-1990 was formed based on the data of the Ukrainian State Register of persons affected due toChornobyl accident (SRU). The identification of thyroid cancer cases (216) was carried out by linking the SRU data-base with the National Cancer Registry of Ukraine (NCRU) data. Standardised incidence ratios (SIR) were estimatedcomparing thyroid cancer incidence in the cohort with the corresponding national indices. Excess absolute risk(EAR), excess relative risk (ERR) and attributable fraction of risk (AR) were calculated accounting for the alterna-tive dose estimates. The following sources of the average dose values for Ukrainian liquidators were used: officialtotal external dose records according to UNSCEAR 2008 report and results of external red bone marrow dose recon-struction by the RADRUE method for the cohort sample. For the radiation risk evaluation, these estimates were con-versed to the average external thyroid dose.

RESULTS

Results of the long term study (1986-2012) of thyroid cancer risks in a cohort of 150813 Chornobyl clean-up workers («liquidators») from Ukraine are presented. Two options for the average thyroid dose estimates were usedfor radiation risks evaluation. According to the SRU and NCRU 216 incident thyroid cancers were diagnosed in 1986-2012 within the studied cohort with an overall SIR of 3.35 (95 % confidence interval (CI) 2.51-3.80). The SIR esti-mates were elevated throughout the entire follow-up period. Investigation of a contribution of the external expo-sure (according to the alternative values) showed the elevated dose associated thyroid cancer rates in the studiedcohort. Alternatively estimated EAR/104 PY Gy were of 1.86 (95 % CI 0.47-3.24) and 2.07 (95 % CI 0.53-3.62);ERR/Gy - 2.38 (95 % CI 0.60-4.15) and 2.66 (95 % CI 0.68-4.64) and AR % (Gy) 70.4 % and 72.7 % Gy.

CONCLUSIONS

Obtained results prove the dose dependent increase of thyroid cancer incidence among UkrainianChornobyl clean-up workers. These conclusions are consistent with those received for combined cohort of Belarus,Russia and Baltic States liquidators.

Experience of study of the incidence of malignant neoplasms population in small areas of Ukraine, which suffered contamination with radionuclides due to the Chornobyl accident

GOAL OF THE STUDY

to evaluate the dynamics of implementation risks of malignant tumors in some small areas of Ukraine in the pre- and post-accident period.

MATERIALS AND METHODS

The study population group - the population of the Malyn rayon, Zhytomyr region. The period of observation covered 1980-2014. There was investigated the incidence of malignant tumors in general and individual nosological forms (thyroid cancer, breast cancer, tumors of hematopoietic and lymphoid system). Methods of variation statistics and descriptive epidemiology were used.

RESULTS

Characteristics of ionizing radiation influence on the population of Malyn rayon indicate the potential for negative effects, especially for thyroid cancer. Besides the fact that the average total effective radiation dose whole body by radioactive cesium in Malyn rayon population (5.9 mSv) are at medium level in Zhytomyr region and is significantly lower in comparison with those of other areas of the northern part of the oblast, the exposure of thyroid 236 mGy, is significantly higher than the regional figures - 81 mGy. Although the level of morbidity Malyn rayon of malignant tumors in general was about at the national level for 1999-2003 and lower it in the 2012-2014, exceeding the figures of Zhytomyr region, the incidence of thyroid cancer in the 2012-2014 in Malin area was 1.7 times higher in comparison with data for Ukraine and in 1.9 times in comparison with the data in Zhytomyr region. As in most northern areas that fell under radioactive iodine fallouts, there is the realization of increased radiation risk of cancer of this organ. The incidence of breast cancer in female population Malyn rayon is the lowest in comparison with Ukraine and Zhitomir regions. However, the rate of increase in this area is the highest.

CONCLUSIONS

The results indicate the need for further monitoring of occurrence of cancer cases in the population of not only Ukraine as a whole, or large administrative units, but also among the population in small areas, taking into account the probability of the realization of risks of radiation-associated disease cases according to local environmental conditions.

Quarter of century since the Chornobyl accident: сancer risks in affected groups of population

Objective. The goal of this study was to define levels and dynamic trends of cancer incidence at whole and some separate sites in groups of Ukrainian population affected by the Chornobyl accident during a long period of observation. Materials and methods. Those groups were Chornobyl accident recovery operation workers (CRW) of 1986-1987 years of participation, evacuees from Prypyat town and 30-km zone and residents of the most contaminated territories of Ukraine. Analysis was carried out with the standard methods of descriptive epidemiology: calculation of crude, age-specific and age-adjusted incidence rates with standard errors and confidence intervals. Results, discussion and conclusions. This study showed that all cancer incidences exceeded the national level only in CRW group. Decrease of cancer incidence rate in the recent years might be caused by shortened average life expectancy in Ukrainian population, especially in males. Statistically significant increase of leukemia incidence in CRW group was registered as well. Besides, in all three main affected groups there was revealed significant excess of thyroid cancer. Irradiation of thyroid due to radioactive iodine fallouts might be a main cause of this phenomenon. Increase of thyroid cancer incidence was registered not only in children, but also in adolescents and adults. Appearance of excess thyroid cancer cases as an effect of radiation exposure tends to increase during the time. Significant excess was also revealed for breast cancer in female CRW group. Because latency period for different nosological forms of radiation-induced malignant tumors varies widely, profound attention in further studies should be drawn not only to thyroid, breast cancers and leukemia, but also to malignancies with longer latent period: lung, stomach, colon, ovary, urinary bladder, kidney cancer and multiple myeloma.

Age and gender patterns of thyroid cancer incidence in Ukraine depending on thyroid radiation doses from radioactive iodine exposure after the Chornobyl NPP accident

The objective of this study was to investigate the thyroid cancer incidence in a whole territory of Ukraine and to clear up its age and gender patterns depending on average regional (oblast) thyroid doses from radioactive iodine due to the Chornobyl accident. MATERIALS AND METHODS. On the basis of average accumulated thyroid doses from radioactive iodine the geographical regions of Ukraine with low and high average thyroid doses were identified for a comparative analysis performance. Methods of descriptive epidemiology were used.

RESULTS

The level and dynamics of thyroid cancer incidence were analyzed in different gender and age groups (both for attained age and age at the moment of the Chornobyl accident). Results of this study confirmed the radiation excess of thyroid cancer in individuals who were children and adolescents in 1986. Some excess was observed in elder age groups too. Especial situation was observed in female age group 40-49 at the moment of the Chornobyl accident i.e. the age-specific thyroid cancer incidence rates were significantly higher in "high exposure" regions comparing with "low exposure" ones during all years of observation within 1989-2009.

CONCLUSIONS

A probable radiation excess of thyroid cancer was suggested not only in children and adolescents but also in adult age groups. In elder age groups this excess was less expressed and manifested after a longer period of time. The origin of the phenomenon in female age group of 40-49 is unclear now. Hypothesis of combined effect of radiation and natural changing of hormonal status in this age should be checked in the future studies.

Multiple myeloma among Chornobyl accident clean-up workers - state and perspectives of analytical study

The objective of the study was to analyze the Multiple Myeloma (MM) incidence in clean-up workers preparing the information background for consequent analytical study with a dose-dependent risk estimates.

MATERIALS AND METHODS

The Cohort Database was linked to the Ukrainian National Cancer Registry to identify the MM cases in a cohort of 152 520 male clean-up workers.

RESULTS

The 64 MM cases were identified in the studied Cohort for the 1987-2012 period. Fifty-eight of them were included to the preliminary incidence analysis accounting for the 10-years lag-period. According to the preliminary data analysis the MM incidence rate in studied clean-up workers Cohort did not exceed the corresponding rate in general population of Ukraine along the 21 years after the catastrophe.

CONCLUSIONS

Standardized incidence ratio for the 2008-2012 period, that is 22-26 years after the accident, demonstrated the significant excess of MM incidence among male clean-up workers in comparison with general population of Ukraine of corresponding age and gender (SIR 1.61, 95% CI 1.01;2.21).

Cancer incidence and nuclear facilities in Ukraine: a community-based study

The study goal was to investigate malignant tumors incidence in 5 Ukrainian cities with nuclear hazardous enterprises: extractive, processing enterprises of uranium ore (Zhovti Wody and Dniprodzerzhynsk of Dnipropetrovsk region) and nuclear power stations (Energodar of Zaporizhska region, Pivdennoukrainsk of Mykolayivska region, Netishyn of Khmelnytska region).

MATERIALS AND METHODS

average annual population of the cities under study in 2003-2008 was 439 600 persons. Total and specific cancer incidence was investigated. Site specific incidence was analyzed for malignancies proved to be radiosensitive in previous studies: trachea, bronchus and lung, breast, kidney, thyroid cancer and leukemia. Data on cancer cases were received in National Cancer Registry of Ukraine (National Cancer Institute). There was used the data of the State Statistics Committee of Ukraine on the size of the studied population by gender - age groups. Standardized incidence ratio of cancer at a whole and for each of five specific forms of malignancies were calculated for the population of each city and group of cities depending on the nature of industrial activity.

RESULTS

During the observed period there were registered 9 381 cancer cases in inhabitants of Ukrainian cities with radiation hazardous facilities. There was stated that cancer incidence rate in population of 5 cities significantly exceeded national and regional levels. Among specific forms of malignancy there were observed excess of lung, trachea, bronchus, breast, kidney cancer and leukemia in population of extractive, processing uranium ore cities. No excess of thyroid cancer was identified. In cities with nuclear power station there were registered excess of kidney cancer.

CONCLUSION

Results of the study suggest the necessity to explore the role of various factors in forming the identified cancer incidence features in the Ukrainian population living near the nuclear power facilities.

[Informative value of the specialized registers in research of leukemia in Chernobyl accident liquidators in Ukraine]

The article considers the possibility of the use of current infrastructure of specialized population registers of Ukraine to study leukemia and other systemic blood diseases revealed in Chernobyl accident liquidators. Advantage and limitation of such registers in the use are discussed in the article. Ukrainian state register of people who suffered from Chernobyl accident and Ukrainian national cancer registers are the largest population registers in the country, which cover all the territory of Ukraine and contain information on each individual and may serve as source base for epidemiological studies. To solve issues on leukemia and other oncological diseases is recommended to use in complex data of specialized registers of Ukraine. It should be also taken into account necessity of using late registered cases and verifying registered diagnoses.