Do PCBs cause cancer?
EPA evaluates the ability of a chemical to cause cancer based on the weight of evidence of human epidemiological and animal toxicity studies. EPA also develops risk factors that indicate the relative potency of the chemical (the ability of a given quantity or dose to cause cancer). Weight of Evidence: PCBs are classified as probable human carcinogens or likely to be carcinogenic in humans. As described in the IRIS file, the basis for this determination is a 1996 study in rats (sponsored by General Electric; reviewed by EPA and external peer reviewers) that found increased numbers of liver tumors in female rats exposed to Aroclors 1260, 1254, 1242 and 1016 and in male rats exposed to Aroclor 1260. These mixtures contain overlapping groups of congeners that, together span the range of congeners most often found in environmental mixtures. The findings of the 1996 GE study strengthened earlier studies which also demonstrated carcinogenicity in rats. Several epidemiological studies on human
