Atomic bomb blast victims lucky enough to survive one cancer have a high risk of developing a second, U.S. researchers said on Wednesday, in a study that offers new insights about cancer risks from radiation exposure.

The findings are important because researchers use information gained from atomic bomb survivors in Japan to predict the risks of radiation exposure from other sources, including cancer risks from medical imaging.

We found that radiation increases the risk of developing a second cancer in a very similar way to how it is related to risk of a first cancer, said Dr. Christopher Li of Fred Hutchinson Cancer Research Center, who led the study published in the journal Cancer Research.

We also found that cancer survivors had particularly high risks of developing a second cancer that we know to be radiation-sensitive. These include breast, colon, lung, thyroid and bladder cancers, he said.

The researchers analyzed data from a group of atomic bomb survivors from Hiroshima and Nagasaki who were followed from 1950 -- five years after the bombings -- to 2002.

The study tracked 10,031 primary cancer survivors -- 1,088 of whom went on to develop second primary cancers.

Cancers of the stomach, lung, liver and breast were the most common, either as a first or a second cancer.

Our findings suggest that cancer survivors with a history of radiation exposure should continue to be carefully monitored for second cancers, Li said.

Li acknowledged it is difficult to extrapolate results to other radiation exposures, because atomic blast survivors were exposed to radiation all over their bodies. Radiation exposure from medical imaging or even cancer treatments are typically limited to one area of the body.

Nevertheless, he said, the findings would likely hold true for other types of radiation exposures known to cause cancer.

The study was done in collaboration with researchers at the Radiation Effects Research Foundation in Hiroshima and Nagasaki and the National Cancer Institute.

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