ANALYSIS OF THYROID CANCER INCIDENCE AND MORTALITY TRENDS AMONG THE RESIDENTS OF THE

Women aged 50–64 and men aged 55–69 are most often affected in Ukraine. The highest mortality rate is reported for the age range of 70–84 years for both males and females. Conclusions. During 2014–2021, the incidence and mortality rates among the population of Ukraine remained at a stable level and were lower compared to global indicators. Since 2017, the Sumy region has been presenting with a decrease in the incidence rate, which corresponds to European trends. In the Sumy region, papillary thyroid cancer remains the most common histological variant. In general, the shares of papillary, follicular, medullary, and anaplastic cancers are consistent with the European figures. In general, the age trends in Ukraine and other countries of the world are similar.


INTRODUCTION / ВСТУП
According to the latest data from Global Cancer Statistics 2020, thyroid cancer was diagnosed in 586,000 people worldwide.Due to these figures, this cancer type ranks ninth in the structure of malignant neoplasms.The incidence among women is 10.1 per 100,000 population, which is three times higher than among men.Thyroid cancer mortality rates are relatively low in women and men (0.5 and 0.3 per 100,000 population, respectively).In total, this malignancy caused 44,000 deaths in 2020 [1].
The highest incidence among representatives of both sexes is observed in North America, Australia/New Zealand, East Asia, Southern Europe, and Micronesia/Polynesia. Cyprus remains the undisputed leader in terms of morbidity among men and women, while South America and Micronesia/Polynesia are leading only among women [2].
According to the data of the 2020 National Cancer Registry, the incidence of thyroid cancer in Ukraine is 5.5 per 100,000 population.Among women, this indicator is traditionally higher than among men (8.6 vs. 2.2 per 100,000 population, respectively).Mortality rates are 0.3 (in women) and 0.3 (in men) per 100,000 population [3].
Thyroid cancer is a complex problem.The only proven risk factor is ionizing radiation, especially in childhood [4].Some studies demonstrate the role of being overweight, tall stature, hormonal influence, salts of heavy metals, and other toxic substances as risk factors.
Since the 1980s, most countries in the world have seen a rapid increase in the incidence rate and a relatively stable or even decreasing mortality rate [5].
The objective of our study was to analyze the thyroid cancer morbidity and mortality trends in the Sumy region during 2014-2021, to study the prevalence of histological variants and sex-age-specific characteristics, and to compare them with all-Ukrainian and global data.
Materials and Methods.The materials of the National Cancer Registry of Ukraine for 2014-2021 and biopsy results logs of the Sumy Regional Clinical Oncology Dispensary were used for the research.Global trends were monitored using the Global Cancer Statistics data.Scientific literature analysis was carried out in PubMed, Scopus, Web of Science networks.Standard statistical methods (analysis of mean values, standard deviation) were used to process the results.
Study results.According to the National Cancer Registry of Ukraine, 24,626 people were diagnosed with thyroid cancer between 2014 and 2021, including 4,556 men (18.5%) and 2,0070 women (81.5%).On average, 3078.25 ± 136.15 people were diagnosed per year.The incidence rate among women is 3.8 times higher than among men.The average incidence rate in Ukraine in 2014-2021 was 6.5 per 100,000 population, while in the Sumy region -8.9 per 100,000 population.The average mortality rate was somewhat higher among women of the Sumy region than that on a nationwide scale (0.6 vs. 0.4 per 100,000 population).The corresponding data are presented in Table 1 and Table 2 For the period from 2014 to 2021, the total incidence in the Sumy region was 26.9% higher than that in Ukraine. Figure 1 clearly shows this difference in incidence rates.
The average mortality rates among residents of the Sumy region and Ukraine did not differ and amounted to 0.4 per 100,000 population.A distinctive feature was represented by the lower male and higher female mortality rates in the Sumy region compared to all-Ukrainian indicators (0.2 versus 0.3 per 100,000 population and 0.6 versus 0.4 per 100,000 population, respectively).
We analyzed the incidence of thyroid cancer in different districts of the Sumy region (Table 3).Taking into account the average rate of morbidity in Ukraine, all districts were tentatively divided into three groups:

Figure 2 -Age-specific incidence of thyroid cancer in the female population of Ukraine in 2014-2021
Among men, the situation is somewhat different.The highest incidence rate is observed in older age groups compared to women: 55-59, 60-64, and 65-69 years (Fig. 3).
The study of histological types of thyroid malignancies demonstrated that papillary cancer was the most common variant (70.5 to 81.9%).The specific share of follicular cancer ranged from 12.8 to 19.2%.The medullary variant occurred much less oftenin 1.5 to 4.6% of cases, while undifferentiated and squamous cell cancer was extremely rare (0.2 to 3.3% of cases).

Discussion
The incidence of thyroid cancer in the Sumy region and Ukraine is lower than the average world indicators.According to the data we obtained, the average incidence rate among women in Ukraine from 2014 to 2021 was 6.5 per 100,000 population, and in the Sumy region, it was 8.9 per 100,000 population, while the world average was 10.1 per 100,000 population.
The incidence rate among men in the Sumy region was slightly higher than the world rates (3.5 versus 3.4 per 100,000 population), while in Ukraine, this parameter was significantly lower (2.6 versus 3.4 per 100,000 population).
Higher incidence rates among Sumy region residents vs. Ukraine were probably due to belonging to the radioactive contamination zone after the Chernobyl nuclear power plant accident.
In Buryn district, Velyka Pysarivka district, Konotop district, Krasnopillia district, Krolevets district, Lebedyn district, Nedrygailiv district, Putyvl district, Sumy district, Trostyanets district and the city of Sumy, a significantly higher incidence rate was observed compared to other districts.We believe this was primarily due to the improvement of diagnostic capabilities at the central district hospitals as a consequence of the medical reform implementation and the purchase of modern equipment.High indicators in the city of Sumy were undoubtedly related to greater accessibility of medical services for the population.In sparsely populated areas, statistics can be influenced even by a few patients.As a result, there may be an impression of a high prevalence of thyroid cancer in a certain area.According to GLOBOCAN 2012, there were 229,900 cases of thyroid cancer in the world [6], while in 2020, this number increased to 586,000 [1].The rapid increase in incidence is explained by the widespread use of ultrasound diagnostics and other imaging methods [7].It made it possible to detect many subclinical thyroid lesions, which are very common in the general population [8].In Denmark, Norway, Ireland, the United Kingdom, and Japan, overdiagnosis occurred in 50-70% of cases, while in the Republic of Korea, Belarus, China, Italy, Croatia, Slovakia, and Francein 80-95% of cases [9].In this regard, many national and international practice guidelines have been revised, and it is now recommended against screening for thyroid cancer.
The active surveillance of microcarcinomas was chosen instead [10].
Schuster-Bruce et al. analyzed the trends of thyroid cancer incidence and mortality in 15 countries of the European Union, the United States of America, Australia, Canada, and Norway.
According to the researchers' conclusions, the trend toward a decrease in incidence and mortality rates has emerged in all countries except for the United States of America, Australia, and Denmark [11].
Average thyroid cancer mortality rates among men and women are lower in Ukraine compared to global rates.During 2014-2021, these rates remained stable; no downward trend was observed.The overestimated figures for 2021 were also related to the use of the Ukrainian standard, so we do not consider them informative for the present time.

Figure 1 -
Figure 1 -Comparison of thyroid cancer incidence rates among residents of the Sumy region and Ukraine for the period from 2014 to 2021

Figure 3 -
Figure 3 -Age-specific incidence of thyroid cancer in the male population of Ukraine in 2014-2021

Figure 4 -
Figure 4 -Age-specific thyroid cancer mortality in the female population of Ukraine in 2014-2021

Figure 5 -
Figure 5 -Age-specific thyroid cancer mortality in the male population of Ukraine in 2014-2021

Table 1 -
. Thyroid cancer incidence and mortality rates among the residents of Ukraine in 2014-2021

Table 2 -
Thyroid cancer incidence and mortality rates among the residents of the Sumy region in 2014-2021

Table 3 -
Thyroid cancer incidence among the residents of Sumy and Sumy region in 2014-2021