Exposure to permethrin and cancer risk: a systematic review

No systematic reviews are available on data from humans on cancer risk from exposure to permethrin, a widely used insecticide for which some animal studies have reported positive findings based on mechanisms that may not be relevant to humans. We identified potentially relevant articles through a search of electronic databases which included all studies of pesticide exposure and human cancer. A total of 18 articles were selected, including six identified from the list of references of other articles. Most articles were based on analyzes of the Agriculture Health Study (AHS); they provided no evidence of an increased risk of cancers of colon, rectum, pancreas, lung, melanoma, female breast, prostate, urinary bladder, as well as non-Hodgkin lymphoma (including its main subtypes), and leukemia. An increased risk of multiple myeloma was reported among AHS members with the highest tertile of estimated permethrin exposure (odds ratio 5.01; 95% confidence interval 2.41-10.42; p for trend <0.01). A subsequent analysis with a larger number of cases found a less pronounced association between permethrin exposure and risk of multiple myeloma; no exposed cases were reported in a separate study. Two case-control studies of childhood leukemia reported an association with biological markers of permethrin metabolites; in another study self-reported exposure to permethrin was associated with risk in children below 1 year of age, but not in older children. In conclusion, permethrin exposure does not seem to entail a risk of cancer in humans. Results on multiple myeloma and childhood leukemia are weak and inconsistent, and require replication in independent populations.