An evaluation of the carcinogenic hazard of 1,4-dichlorobenzene based on internationally recognized criteria.

1,4-Dichlorobenzene (1,4-DCB) was shown to induce the formation of male rat renal tubule tumors and male and female mouse liver tumors when administered in a chronic bioassay. Since the original carcinogenicity findings, an extensive body of mechanistic information has been developed to elucidate the mode of action by which 1,4-DCB induces these effects and to evaluate the human relevance of the observed animal tumors. In addition, some regulatory and authoritative bodies (U.S. EPA and IARC) have developed rigorous scientific criteria for the amount and types of evidence needed to establish that a material causes kidney toxicity and tumors in male rats through a specific mechanism, alpha-2u-globulin nephropathy. This paper summarizes the mechanistic data developed for 1,4-DCB, which affords an understanding of the lack of human relevance of the male rat renal tubule tumors and mouse liver tumors; assesses that mechanistic data set utilizing the defined set of evaluation criteria formulated by U.S. EPA and IARC for alpha-2u-globulin nephropathy; and discusses the predictive power of mechanistic data developed to elucidate the mode of action of 1,4-DCB in inducing mouse liver tumors. Finally, there is a discussion of how some, but not all, regulatory and authoritative bodies have incorporated this substantial mechanistic data set for 1, 4-DCB into their cancer hazard evaluations and concluded that 1, 4-DCB presents little, if any, cancer hazard to humans.