A CASE-STUDY OF CANCER DATA SET COMBINATIONS FOR PCBS

Results of several animal bioassays have demonstrated the carcinogenic potential of polychlorinated biphenyl (PCB) mixtures. Although PCBs a re no longer manufactured, cancer risk assessment for PCBs remains an important issue because of continued potential human exposure from man y sources. The existing cancer risk estimate for PCBs used by the U.S. EPA is based on liver tumors observed in female Sprague-Dawley rats i n a lifetime bioassay. Liver cancer has been observed in other long-te rm bioassays as well. In this case study, experimental designs and bio logical characteristics of the data from these studies were evaluated to determine whether a combination of the data sets is scientifically reasonable. A statistical analysis of the data sets based on likelihoo d ratio theory was used to assess the compatibility of individual data sets to a common multistage dose-response model. The results from the se biological and statistical assessments suggest that at least two da ta sets could be combined to derive a quantitative risk estimate for P CBs. Increased confidence in the quantitative estimate would result fr om such combination because more data are being used to assess the dos e-response relationship. (C) 1995 Academic Press, Inc