Critical Evaluation of Diazinon's Breast Cancer Risk

Diazinon is a widely used organophosphate insecticide. Non-agricultural use of diazinon exceeds its agricultural use, creating the potential for widespread non-occupational exposures. Although widely used, there has been no cancer risk classification for diazinon by the US Environmental Protection Agency (EPA), the National Toxicology Program (NTP) or International Agency for Research on Cancer (IARC). For this report, we have used a modification of the IARC approach to conduct a detailed evaluation of any direct or related evidence of cancer risk from exposure to diazinon, with a focus on breast cancer risk. We have critically evaluated all the available human, experimental animal, and cancer-related molecular and mechanistic studies on diazinon. Chemical and up-to-date regulatory information is included, as well as a discussion of diazinon's environmental fate and potential for human exposure. Evidence available so far does not indicate that diazinon increases breast cancer risk. It should be noted that this conclusion is based on the limited scientific evidence currently available. We have identified several research gaps in the report. We propose that diazinon be classified in Group 3. In the Program on Breast Cancer and Environmental Risk Factor's (BCERF) breast cancer risk classification scheme (see Appendix B), this group represents chemicals that are not classifiable for breast cancer risk in humans.