Thyroid cancer incidence trends in Belarus: examining the impact of Chernobyl.

BACKGROUND While prior studies of thyroid cancer incidence within Belarus have increased since the 1986 Chernobyl reactor accident, the magnitude of increase is not well quantified. METHODS Using Belarussian national cancer registry data, trends in average annual age-adjusted thyroid cancer incidence rates were examined by calendar year and gender. Incidence rates were also examined across specified time intervals, for specific age groups at diagnosis, and in 'higher exposure' regions compared with 'lower exposure' areas. RESULTS Age-adjusted thyroid cancer incidence rates (adjusted to the WHO 2000 world population) have increased between 1970 and 2001 from 0.4 per 100 000 to 3.5 per 100 000 among males (+775%) and from 0.8 per 100 000 to 16.2 per 100 000 among females (+1925%). The relative increase among males (+1020%) and females (+3286%) in 'high exposure' areas exceeded increases among males (+571%) and females (+250%) in 'lower exposure' areas of Belarus. Dramatic increases in thyroid cancer incidence rate ratios were noted among both males and females and in all age groups. The highest incidence rate ratios were observed among people from 'higher exposure' areas ages 0-14 yr at time of diagnosis. CONCLUSIONS Marked increases in the incidence of thyroid cancer have occurred over a relatively limited period of observation in all areas of the Republic of Belarus and among all age categories. The greatest increases have occurred among children, suggesting that a high prevalence of pre-existing iodine deficiency in combination with unique susceptibility among younger people might have contributed to potential carcinogenic exposures to the thyroid.