Epidemiologic studies raise concern

Epidemiologic studies raise concerns about the potential carcinogenicity of PCBs, although the specific results differ by study. Capacitor manufacturing workers exposed to a variety of commercial PCB mixtures containing 41–54% chlorine had increased mortality from liver, gall bladder, and biliary tract cancer (Brown 1987), gastrointestinal tract cancer (Bertazzi et al. 1987), or malignant melanoma (Sinks et al. 1992). An analysis of these and a smaller study (Gustavsson et al. 1986) found the combined results significant for liver, gall bladder, and biliary tract cancers, and for malignant melanoma (Nicholson et al. 1994). Earlier, petrochemical refinery workers exposed to Aroclor 1254 and other chemicals had shown significantly increased mortality from malignant melanoma (Bahn et al. 1976). More recently, electric utility workers exposed to PCBs had significantly increased mortality from malignant melanoma and brain cancer (Loomis et al. 1997).
Recent case-control studies have found associations between non-Hodgkin’s lymphoma and PCB
concentrations in adipose tissue (Hardell et al. 1996) and serum (Rothman et al. 1997). In the Rothman

study of persons without known occupational exposure to PCBs, mean PCB blood levels of 13.3 ppb yield highly significant (p=0.0008) increased odds of non-Hodgkin’s lymphoma. Case-control studies have not found significant associations between serum PCBs and breast cancer (Krieger et al. 1994; Wolff et al. 1993) or between concentration of PCBs in bone marrow and leukemia in children (Scheele et al. 1992); these results have not been fully studied for their implications. Hoyer and colleagues (1998) found a dose response relationship between serum concentrations of dieldrin and breast cancer but not with PCBs and DDT. In the previously described Yusho and Yu-Cheng episodes in Japan and Taiwan,
respectively, where humans consumed rice oil contaminated with PCBs, the incidence of liver cancer was increased (Masuda 1994); however, this incidence has been attributed, at least in part, to heating of the PCBs and rice oil, which causes formation of chlorinated dibenzofurans (Morita et al. 1978).