Pesticides and childhood cancer: an update.

OBJECTIVES: Epidemiological studies have reported associations between childhood cancer and either parental or child exposure to pesticides. Reviews have been published in 1997, 1998 and 2006 where the evidence was found suggestive but not conclusive. The present review is an extended update of the latter one.
METHODS: The PubMed database was searched to identify published studies on this topic issued between 1998 and 2006.
RESULTS: Thirty-six new studies have been identified for this review. Some cohort studies and the majority of the case-control studies suggest an increased risk for the cancer types studied, associated with exposure to pesticides in at least one of a large variety of exposure categories. However, the evidence is conflicting with regard to cancer types as well as to causative factors across studies. The major shortcomings concern exposure assessment, where, e. g., "farming" is treated equal to "exposure to pesticides", disregarding other possible exposures, e.g., to biological or infectious agents, and hitherto unidentified lifestyle factors. Also, many exposure categories used, mainly in case-control studies, lack chemical or toxicological plausibility. In most studies exposures were categorized as "ever vs. never", with little regard of exposure intensity or duration.
CONCLUSIONS: The available literature does not allow firm conclusions with regard to pesticides and any type of childhood cancer. But even if the reported associations were true, exposure to pesticides could not explain the vast majority of childhood cancer cases. Investing in the acquisition and critical review of exposure information appears to be the crucial step for causal assessment in future research. However, focusing on the presence of pesticides, and not asking the question why they were used, might mask relevant associations to other causative agents.