Cancer risk among chernobyl cleanup workers in Estonia and Latvia, 1986–1998

Abstract

Two cohorts of Chernobyl cleanup workers from Estonia (4,786 men) and Latvia (5,546 men) were followed from 1986 to 1998 to investigate cancer incidence among persons exposed to ionizing radiation from the Chernobyl accident. Each cohort was identified from various independent sources and followed using nationwide population and mortality registries. Cancers were ascertained by linkage with nationwide cancer registries. Overall, 75 incident cancers were identified in the Estonian cohort and 80 in the Latvian cohort. The combined-cohort standardized incidence ratio (SIR) for all cancers was 1.15 (95% confidence interval (CI) 5 0.98-1.34) and for leukemia, 1.53 (95% CI 5 0.62-3.17; n 5 7). Statistically significant excess cases of thyroid (SIR 5 7.06, 95% CI 5 2.84-14.55; n 5 7) and brain cancer (SIR 5 2.14, 95% CI 5 1.07-3.83; n 5 11) were found, mainly based on Latvian data. However, there was no evidence of a dose response for any of these sites, and the relationship to radiation exposure remains to be established. Excess of thyroid cancer cases observed may have been due to screening, the leukemia cases included 2 unconfirmed diagnoses, and the excess cases of brain tumors may have been a chance finding. There was an indication of increased risk associated with early entry to the Chernobyl area and late follow-up, though not statistically significant. Further follow-up of Chernobyl cleanup workers is warranted to clarify the possible health effects of radiation exposure. ' 2006 Wiley-Liss, Inc. Key words: neoplasms; incidence; cohort; Chernobyl; Estonia; Latvia; radiation effects After the reactor accident at the Chernobyl nuclear power station in April 1986,~600,000 persons from throughout the former Soviet Union were sent to the Chernobyl area for environmental cleanup and related activities. 1 The cleanup workers, also known as liquidators, remained in the area for an average of 3 months. 2 Although average radiation doses to these workers are now known to have been low,~0.1 Gy, some workers received higher doses. 3,4 To assess cancer risks related to working in a radioactively contaminated area, cohort studies of cleanup workers in Belarus, 5 Ukraine, 6 the Russian Federation, 7 Lithuania, 8 Latvia 9 and Estonia 10 were initiated.The first results on cancer incidence and cause-specific mortality of the Estonian Study of Chernobyl Cleanup Workers covered the period 1986-1993. 10 No significant increase in the incidence of any cancer was found; however, significant excess cases of suicide deaths were observed. To evaluate further the possible effect of radiation exposure on the incidence of leukemia and other cancers among Chernobyl cleanup workers, a Baltic cohort was established. Here we report the results from Estonia and Latvia. Material and methodsThe establishment of the Chernobyl cleanup worker cohort in Estonia has been described in detail. 2 In brief, the cohort was assembled in 1992 using multiple data sources, including the General Staff of Estonian Defence Forces, the former Estonian Chernobyl ...

Site-specific cancer risk in the Baltic cohort of Chernobyl cleanup workers, 1986–2007

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