Thyroid Cancer Among Chornobyl Clean-up Workers in Ukraine: Pilot Study
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.
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.
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
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.
Kiyohiko Mabuchi, M.D.
National Cancer Institute (NCI)
United States: Federal Government
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