Dichlorvos and carcinogenicity: a systematic approach to a regulatory decision

On the request of the Belgian Health Council, the authors performed a systematic review of the available evidence in the literature and in expert panel reports, with regard to a possible carcinogenic effect of dichlorvos. Following the evaluation procedure developed by IARC, they first concluded that dichlorvos should be classified as a possible carcinogen for man. This preliminary conclusion, and its possible consequences of withdrawal of several product authorizations, was then communicated by the Health Council to all stakeholders. As a result, the interpretation of the animal experimental data was confronted with the conclusions of a U.S. "Blue Ribbon Panel" of independent experts, who reviewed all the data that were available to them. After an exchange of views, the Health Council downgraded its classification of dichlorvos toward nonclassifiable with regard to cancer in man. This paper describes the review and decision-making processes, focusing on the major arguments underlying the original interpretation of the animal data and its eventual modification.