Workshop to identify critical windows of exposure for children's health: Cancer work group summary

We considered whether there are discrete windows of vulnerability in the de velopment of cancer and which time periods may be of the greatest importanc e. Cancer was considered broadly. including cancers in childhood as well as adult cancers that may have an in utero or childhood origin. We concluded that there was evidence from animal and epidemiologic studies for causal re lationships for preconceptional, in utero, and childhood exposures and canc er occurrence in children and adults. However, the evidence is incomplete a nd all relevant critical windows may not have been identified. The comprehe nsive evaluation of the relative importance of specific time windows of exp osure is limited. Improvements in the design of epidemiologic studies and a dditional animal studies of mechanisms are warranted.