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Study of Leukemia and Other Hematological Diseases Among Clean-up Workers in Ukraine After Chernobyl

Several years after a 1988 agreement between the United States and the USSR to cooperate in the area of nuclear reactor safety, the National Cancer Institute (NCI), NIH undertook to develop a study of leukemia risk among Ukrainian men potentially exposed to external radiation during clean-up operations (e.g., liquidators) following the Chernobyl accident. Responsibility for the study resides in the Radiation Epidemiology Branch of NCI.

Leukemia, a malignancy arising from the bone marrow, is strongly associated with radiation exposure because of the sensitivity of the bone marrow to the carcinogenic effects of external radiation. Leukemia is also among the earliest cancer sites to show an increase following radiation exposure, and one of the malignancies most consistently associated with external radiation exposure. Evaluating leukemia risk among the Chernobyl clean-up workers was important both in and of itself and also because of the information it would provide about risks to individuals in similar circumstances involving protracted exposure, such as nuclear workers.

Efforts to develop a research plan for studying leukemia among clean-up workers in Ukraine began as early as 1989-1990. A pilot phase, conducted between 1997-1999 to establish the feasibility of the proposed investigation, showed that a suitable cohort could be assembled and that representative clean-up workers could be located and interviewed regarding their experience during the clean-up operations. Leukemia cases were registered in hematologic facilities in central oblast dispensaries and the medical records were found to be readily available. A sample of 100 cases of leukemia and related disorders was collected and reviewed by an international group of hematologists and pathologists, with a high level of confirmation of the preliminary diagnoses made by local hematologists.

Program Overview

The cohort consists of approximately 110,000 clean-up workers in Ukraine who worked in the 30 km zone around the plant during 1986-1990 and resided in Kiev City or in one of the following oblasts: Cherkassy, Chernigov, Dnepropetrovsk, Kharkov, Kiev. The cohort was identified through the State Chernobyl Registry. In the first phase of the study, cases of leukemia and other hematologic disorders (specifically multiple myleoma and myelodysplasia ) were sought in all relevant health care institutions and assembled into a leukemia registry. Ultimately, record linkage was used to identify cases occurring among members of the cohort between 1987-2000. For each case, five controls were drawn from cohort members who did not develop hematologic disorders, matched to the case on age and area of residence. To gather information for estimating individual dose, detailed interviews are conducted to obtain data related to cumulative estimated dose to bone marrow. Estimated bone marrow doses based on a specially-developed time-and-motion approach have been evaluated in a statistical analysis (Romanenko et al., 2008) to evaluate the dose response relationship with leukemia risk overall, as well as with two separate subgroups: chronic lymphocytic leukemia (CLL, a hematologic malignancy generally thought not to be related to radiation exposure) and non-CLL cases.

Read the paper summarizing results: Radiation and the risk of chronic lymphocytic and other leukemias among Chornobyl cleanup workers (Environ Health Perspect, 2013).

Benefits to Ukrainians

The major benefit to Ukrainians and the scientific community at large is that the study will address concerns about the health effects of the accident on the workers who were involved with the clean-up. Other benefits include the establishment of a leukemia registry set up to identify all the cases that occurred during 1987-2000. A panel of international experts has provided local hematologists with a valuable opportunity for professional interaction. Publications describing the findings provide important new data on the risks associated with low-dose, protracted exposure to external radiation.

Roles of United States Participants

  • The NCI staff is charged with scientific direction and management of the projects.
  • The external advisory group (LAG) is comprised of recognized experts in the relevant scientific fields. They review the activities of the collaborative studies approximately once a year and report to the Director of the Division of Cancer Epidemiology and Genetics, NCI. Their comments and recommendations are also shared with the collaborating investigators.