X-rays, cancer in China.

X-rays, cancer in China

Everyone knows radiation can cause cancer. But which organs are most vulnerable and under what conditions? In confronting such questions, scientists have relatively few epidemiologic data to go on. That's why a new study in the May 4 JOURNAL OF THE NATIONAL CANCER INSTITUTE is important. While it doesn't reveal any striking new findings, the large number of people studied adds considerably to the epidemiologic-data pot.

Chinese researcher Ji-Xian Wang, John D. Boice of the National Cancer Institute in Bethesda, Md., and their co-workers examined the incidence in China of different cancers among 27,011 radiologists and diagnostic X-ray technicians employed between 1950 and 1980, and compared that to the cancer rate of 25,782 Chinese medical specialists who did not work with radiation. Overall, X-ray workers had a 50 percent higher risk of developing cancer than their colleagues. Like previous but much smaller U.S. and British studies of radiologists, the China study showed that long-term, small-dose exposure can cause leukemia: X-ray workers were 3.5 times as likely to get leukemia. Incidences of breast, thyroid and skin cancers also were higher.

Wang's group reports no excess lung cancer risk among Chinese X-ray workers. This is in marked contrast to the high lung cancer rates reported for Japanese survivors of atomic blasts. "This is one of the first convincing indications that if you split the dose over long periods of time the risk for lung cancer is diminished," Boice says.

The China study is more sensitive than previous work because it examines cancer incidence rather than deaths. Its main limitation is that no exact dosages could be determined since the workers did not use radiation badges.