Decades Later, Chernobyl Accident Yields Clues to Leukemia Risk
Exposure to low doses of ionizing radiation over extended periods of time may raise the risk of chronic lymphocytic leukemia (CLL), as well as other types of leukemia, later in life, new research suggests. The findings are from a study of Ukrainian workers who were exposed to radiation while cleaning up the 1986 Chernobyl nuclear power plant accident.
Twenty years after the disaster, these workers, as a group, had an increased risk of CLL and other forms of leukemia, researchers reported online last week in Environmental Health Perspectives. The case-control study used information from a larger study tracking the health of more than 110,000 Chernobyl cleanup workers.
"Previous research has shown an increased risk of some types of leukemia related to radiation exposure," said lead researcher Dr. Lydia Zablotska of the University of California, San Francisco. "However, none of those studies have reported an association for CLL, so we were intrigued by our findings."
In the new study, Dr. Zablotska's team attributed 19 of 117 cases of leukemia (16 percent) diagnosed in the cleanup workers since the Chernobyl nuclear reactor accident to radiation exposure from the accident. The magnitude of risk was similar for CLL and for other types of leukemia.
CLL is more common than other leukemias in the United States, with some 15,000 cases diagnosed last year. The disease is a relatively benign leukemia, but some patients require chemotherapy and the cancer can be fatal.
In addition to providing clues about the causes of CLL, the new findings could help researchers understand the long-term health effects of exposure to low-dose radiation. "The radiation burden in the United States has increased over the past 20 years, primarily from exposure to CT scans," said Dr. Zablotska. "We want to know what this radiation can do in the long term."
Radiation can cause damage to DNA that eventually leads to cancer. Studies of atomic bomb survivors have documented the cancer risks associated with short-term exposure to moderate and high doses of radiation. Less is known, however, about the health effects of exposure to lower doses of radiation over a longer period of time, such as the doses experienced by the cleanup workers.
In 2008, the research team first reported an association between radiation exposure and CLL in Chernobyl cleanup workers. Because the finding was unexpected, the authors undertook the current study with a larger sample and longer follow-up.
"For researchers, these findings are exciting because they could open up new research into the mechanism of how CLL develops," said Dr. Kiyohiko Mabuchi, who heads the Chernobyl Research Unit in NCI's Division of Cancer Epidemiology and Genetics and is the senior author of the new study.
He noted that other studies of radiation-exposed workers have not detected an increased risk of CLL, so more research is needed to understand these inconsistencies. Identifying the biological mechanism underlying the association will be important, he added.
This study provides "some of the most substantial evidence to date supporting the conclusion that developing CLL is a possible adverse consequence of exposure to ionizing radiation," noted Dr. David Richardson, an epidemiologist at the University of North Carolina, Chapel Hill, who studies the health effects of radiation but was not involved in the research.
"It will be important to continue to monitor health consequences," added Dr. Mabuchi, "both in cleanup workers, as well as in other groups exposed to radiation from the Chernobyl accident."
This research was supported by NCI's Intramural Research Program.