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

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 clean-up workers in Ukraine. In preparation for this study, we plan to conduct a pilot study 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; (iii) to obtain saliva buccal cell samples; and (iv) to obtain information on availability of archival thyroid tumor specimens for future tumor-tissue collection.

ELIGIBILITY:

The cohort includes Ukrainian clean-up workers with the following eligibility criteria: males, first year of service as a clean-up worker (1986-2006); initial registration as a clean-up worker in one of the study areas; and age when first worked at Chornobyl (under 60). For the pilot study, we will select 100-110 cases with thyroid cancer in three study areas, Kyiv, Donetck and Dnipropetrovsk oblasts and controls (with a 4:1 ratio).We will access 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. 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 registry database.