Thyroid cancer among Ukrainians and Belarusians who were children or adolescents at the time of the Chernobyl accident

Abstract

Our objective is to assess the regional and temporal dependences of the baseline cases contributing to thyroid cancer incidence among those exposed in childhood or during adolescence in Belarus and Ukraine after the Chernobyl accident. Data are analysed for Kyiv and Sevastopol City and the 25 oblasts (regions) in Ukraine, and for Minsk and Gomel City and the 6 oblasts in Belarus. Average thyroid doses due to the Chernobyl accident were assessed for every birth year in the period from 1968 to 1985. Case data pertain to people who underwent surgical removal of thyroid cancers during the period 1986 to 2001 and who were allocated to their place of residence at the time of the accident. The 35 oblasts/cities were subdivided into an upper, middle and lower group of baseline thyroid cancer incidence. Poisson regressions were performed to estimate age, time and gender dependences of the baseline incidence rates in the three groups. The majority of oblasts/cities with high average doses and the majority of Belarusian oblasts/cities belong to the upper group of baseline thyroid cancer incidence. The baseline in the upper group is estimated to be larger than in the middle group by a factor of 2.3, and by a factor of 4.0 when compared to the lower group. The baseline incidence increases with age and with time since exposure. Estimated baseline incidence rates were found to increase from 1988 to 1999 by factors of three and two for the upper and the two lower groups respectively. The estimated thyroid cancer incidence rates in Belarus and Ukraine, and their dependences on gender and age, are consistent with observed rates found in the larger cancer registries of other countries. In conclusion, the baseline cases are found to contribute about 70% to the thyroid cancer incidence in Ukraine, and about 40% to the incidence in Belarus.

Identifying a risk profile for thyroid cancer

“…The age at exposure has been shown to be a critical risk factor for developing thyroid carcinoma after exposure to fallout from Chernobyl, with those under the age of 1 showing a much greater risk than older children. There is a rapid decline to a level of relatively low risk for young adults (43,44). A similar situation was portrayed in Nagasaki and Hiroshima, where atomic bomb survivors displayed one of the highest solid tumor risk estimates (45).…”

“…Thyroid cancer is the fastest growing type of cancer in the USA with a 6.3% increase during the period of 1997-2003 and we have data suggesting that in Brazil it is not different (12,64). However, the rate of increase as well as the incidence of thyroid cancer varies in different geographic and ethnic group regions, including individuals exposed to welldefined factors, such as ionizing radiation (44)(45)(46)(47)(64)(65)(66)(67). The question may be posed as to why some individuals are more susceptible to environmental aggressions?…”

Gain of chromosome band 7q11 in papillary thyroid carcinomas of young patients is associated with exposure to low-dose irradiation

“…Estimated dosimetry data were used because no individual dose measurements of the patients were available. The average thyroid dose of the patients was calculated using countyspecific doses that were estimated for inhabitants that were born between 1968 and 1985 (18). Because the patients included in this study were considerably younger (age at the time of exposure, ≈2 y) than the birth cohort 1968-1985, the estimated thyroid dose was corrected by a factor of 2 (19).…”

Childhood thyroid cancer in Belarus, Russia, and Ukraine after Chernobyl and at present

“…Examination of the geographical distribution of diagnosed cases and the estimates of absorbed thyroid doses left no doubts that childhood thyroid cancer cases are associated with exposure to radiation, in particular with intake of 131 I (19,20).…”