The incidence trends of papillary thyroid carcinoma in Belarus during the post-Chernobyl epoch.

Background: The increase of papillary thyroid cancer (PTC) rate among children who were exposed to post-Chernobyl 131-I release was reported only four years after the accident, first in Belarus where the heaviest fallout happened. The evolution of the occurrence of thyroid carcinoma based on the age-period-cohort analysis and the effects of age, period, and birth cohort on time trends aimed to reveal if post-Chernobyl follicular cells irradiation still has been impacting on incidence rate of papillary thyroid carcinoma nowadays.

Methods: The Belarusian Cancer Registry was used to identify patients with PTC diagnosed during the years 1980-2019. The incidence trends were analysed using Join-point regression software.

Results: The highest peak of age-specific incidence curve was shown during the years 1980-2001 in the age group of 15-19 years old that was associated also with short-latency cases of post-Chernobyl PTC. This is the same age group that demonstrated significant growth of the incidence rate during the years 2006-2019, largely because of the increasing number of non-exposed patients with PTC (p < 0.001). Influence of post-Chernobyl exposure also can be seen in the young adults age-groups of patients (for 20-24 years old during the years 1980-2003 and 2013-2019, p < 0.001; for 25-29 years old during the years 1980-1999 and 1999-2011, p < 0.001).

Conclusion: After the Chernobyl accident, epidemiological waves that reflect the age shift of the group of children exposed to 131-I have consistently emerged. Currently, the incidence rate continues to increase only in the cohort of patients aged 20-44 years.