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.

- INCLUSION CRITERIA:

For the pilot study, we will select clean-up workers with thyroid cancer reported in three
study areas, Kyiv, Donetsk and Dnipropetrovsk oblasts and controls (with a case-control
ratio of 1:3) demographically matched to cases. We estimate the number of these cases will
be between 100 and 110. These two oblasts have been chosen to represent an area known,
from the leukemia study, to have a high study participation rate (Kyiv and Dnipropetrovsk
oblasts) and an area newly added and thus unknown regarding participation rate (Donetsk).
All study subjects are males and average about 55 years. In view of the very high survival
rate for thyroid cancer, a majority of the subjects are expected to be alive.

EXCLUSION CRITERIA:

Excluded from the study will be those who cannot be located, refuse to participate in the
study, or do not provide informed consent.