Use of mechanistic data in the IARC evaluations of the carcinogenicity of polychlorinated biphenyls and related compounds.

The IARC Monographs are a series of scientific reviews that identify environmental factors that can increase the risk of cancer in humans. In its first part, the principles and procedures of the IARC Monographs evaluations are summarized. In a second part, we present the most recent IARC evaluation of polychlorinated biphenyls (PCBs) and polybrominated biphenyls (PBBs), performed in February 2013: PCBs and dioxin-like PCBs were both classified into group 1 "carcinogens," while PBBs were evaluated as "probably carcinogenic to humans" (group 2A). Noteworthy is that the relative contributions of different PCB congeners to the carcinogenicity of PCB mixtures are not known. The use of mechanistic data for the classification into a higher category is discussed in the context of the history of the consecutive evaluations of several related polychlorinated compounds.