ScienceDaily (Mar. 13, 2008) — Radiation exposure before birth or during early childhood increased the risk of adult solid cancers, according to a study of survivors of the Hiroshima and Nagasaki bombings.

It is known that radiation exposure during fetal development increases the risk of childhood cancers and that exposure during early childhood increases the risk of adult-onset cancers. However it was not known if radiation exposure to the fetus increases the risk of adult cancers.

To find out, Dale Preston, Ph.D., of the Hirosoft International Corporation in Eureka, Calif., and colleagues at the Radiation Effects Research Foundation in Hiroshima, Japan, calculated the excess risk of solid cancers in adult survivors of the Hiroshima and Nagasaki bombings, relative to non-exposed populations.

Of the 2,452 study participants who were exposed to radiation before birth, 94 have developed adult cancers, as did 649 of the 15,388 individuals who were exposed between birth and six years of age. By age 50, the excess relative risk for those exposed before birth was 1.0 per Sv (a unit for measuring radiation exposure), and for those exposed as young children, it was 1.7 Sv at age 50.

The researchers note that the overall risk of solid cancers increases with age, and so continuing to follow the study participants as they age will be important. Also, the investigators only considered solid cancers, and did not examine the rate of blood cancers, such as leukemia.

"The present data suggested that increases in risks of adult-onset cancer among those exposed to radiation in utero may be smaller than for those exposed in early childhood," the authors write. That said, these data may be important when considering the public health risks of medical and occupational radiation exposure for pregnant women.

This research was published in the March 11 issue of the Journal of the National Cancer Institute.

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