Thyroid Cancer Among Chornobyl Clean-up Workers in Ukraine: Pilot Study

Background:

Much is known about the radiation-related risk of thyroid cancer, but there is considerable uncertainty about the magnitude of the radiation risk among those who were exposed as adults, particularly in males. A large number of clean-up workers, mostly male, who participated in decontamination and clean-up activities after the Chornobyl accident were exposed to external radiation at various levels. An increased thyroid cancer risk has been reported from studies of Russian, Estonian and Latvian clean-up workers, but there is little evidence of a dose response. However, recent published data from an IARC study of thyroid cancer cases and controls pooled from the Chornobyl clean-up workers in Belarus, Russia and Baltic countries show a strong dose response with an estimated risk per unit dose that is much higher than those reported from other irradiated populations exposed as adults. Following the completion of our NCI study of leukemia among Ukrainian clean-up workers, we are proposing a nested case-control study to assess the radiation-related risk of thyroid cancer among the 150,000 male cleanup workers in Ukraine. In preparation for this study, a pilot study is in progress to assess the feasibility of a full study.

Objectives:

The objectives are (i) to identify thyroid cancer cases and demographically matched controls without thyroid cancer occurring among the 150,000 Ukrainian clean-up workers through linkage to the National Cancer Registry and Chernobyl State Registry of Ukraine; (ii) to trace/locate and interview a small sample of subjects with thyroid cancer and their respective controls ; (iii) to obtain saliva buccal cell samples; and (iv) to locate and transfer thyroid tumor specimens from identified cases to the archive maintained at the Research Center for Radiation Medicine (RCRM),for diagnostic verification and possible future genetic/molecular research using the latest available techniques.

Eligibility:

The cohort includes Ukrainian clean-up workers who meet the following eligibility criteria: males, first year of service as a clean-up worker (1986-1990); initial registration as a clean-up worker in one of the study areas; and age when first worked in the Chornobyl zone (under 60). For the pilot study, we will select 100-110 cases with thyroid cancer in three study areas, Kyiv, Donetsk and Dnipropetrovsk oblasts and controls (with a case-control ratio of 1:3). We will assess the feasibility of proxy interview for deceased thyroid cancer cases in the study area.

Design:

This pilot study will be conducted in the framework of the planned nested case-control study in the cohort of Chornobyl clean-up workers but will involve only a small number of subjects with thyroid cancer and their respective controls. Thyroid cancer cases will be identified by linkage to the Cancer Registry of Ukraine. Controls will be identified from the Chernobyl State Registry. Locating archived tumor tissues will be done by search of the Cancer Registry of Ukraine database supplemented by interview data. Consent for transfer of tissues to RCRM will be sought at the time of interview.