THURSDAY, Oct. 28 (HealthDay News) -- While standard models and epidemiological data have suggested that radiation-related cancer risks are higher in children and decrease with increasing age at exposure, mathematical models do not support this for all cancer types, according to research published online Oct. 25 in the Journal of the National Cancer Institute.
Igor Shuryak, M.D., of the Columbia University Medical Center in New York City, and colleagues reanalyzed the Japanese atomic bomb survivor data assuming two different pathways -- initiation of gene mutations and promotion of the number of existing premalignant cells -- through which radiation exposure can ultimately lead to cancer. Using a biologically-based quantitative model of radiation carcinogenesis based on these two premises, the researchers aimed to determine if the risks of radiation-related cancers decreased with increasing age at exposure.
The researchers' model showed that radiation cancer risks in younger individuals are dominated by initiation processes, whereas radiation cancer risks at older ages are more influenced by promotion of preexisting premalignant cells. The balance of risk, however, was found to be cancer site-dependent; for example, radiation-induced breast cancer risk decreases with age at exposure at all ages, but radiation-induced lung cancer risks do not follow this pattern. Overall, radiation-induced cancer risks after exposure in middle age may be twice as high as previously estimated.
"The weight of epidemiological evidence now suggests that, for adult exposures, radiation-induced cancer risks do not generally decrease with increasing age at exposure," the authors write.
Abstract
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