Twenty years after the Chernobyl accident: solid cancer incidence in various groups of the Ukrainian population.

Several major international studies such as those performed on the A-bomb survivors, have shown a clear linkage between the exposure to ionizing radiation and the occurrence of various cancer types including leukemia. While these studies are mostly characterized by high dose rates, studies on populations exposed after the Chernobyl accident are in most cases characterized by low dose rates which are typical for occupational radiation protection. Here, data on more than 60,000 Ukrainian workers who participated in recovery operation works in Chernobyl in 1986-1987, more than 50,000 evacuees from the city of Prypyat and the 30 km zone, and about 360,000 residents of most contaminated territories are presented, which cover a period of observation from 1980 to 2004. For all cancers combined, statistically significant higher incidence rates than the national rates were found only for the recovery workers (standardized incidence ratio (SIR) 117.2%, 95% confidence interval: 114.1-120.3), while those for the other investigated groups were lower. In all groups under study a significant increase of thyroid cancer incidence rates has been registered. This increase appears to be associated, at least partly, with the fallout of radioiodine, and it was found not only in children, but also in adolescents and adults. For example, the most significant excess was found for male recovery workers corresponding to a factor of 8.0. It is important to keep in mind, however, that the contribution of confounding factors such as an intensified thyroid screening after the Chernobyl accident could not be quantified, in the present study. For female recovery workers there was also an excess of breast cancer over the national rates (SIR 190.6%; 95% confidence interval: 163.6-217.7%). An analysis of the two other groups (evacuees and residents of contaminated territories) gave controversial results: relative to the local standard there was a statistically significant excess, while comparison with the national level did not substantiate this conclusion.