Malathion and malaoxon: histopathology reexamination of the National Cancer Institute's carcinogenesis studies.
In the early 1970s the National Cancer Institute (NCI) studied malathion and the oxygen analog, malaoxon, for possible carcinogenicity in rats and mice. The results from these long-term studies were reported in three NCI Technical Reports with the conclusions that neither chemical was shown to be carcinogenic in rodents. In response to the renewed public health interest and concern about the increasing use of malathion in agriculture and especially its use to eliminate Mediterranean fruit fly infestations in California and Florida during the 1980s, the National Toxicology Program (NTP) in consultation and agreement with the NCI reevaluated the histopathology of the NCI studies of malathion in Osborne-Mendel and Fischer 344 rats and of malaoxon in Fischer 344 rats. The NTP histopathology reexamination confirmed the original NCI interpretative conclusions that malathion was not carcinogenic. For the malaoxon study, the only difference between the original and subsequent interpretations was for C-cell neoplasms of the thyroid gland, in that the NTP concluded there was equivocal evidence of carcinogenicity for male and female F344 rats.
D000818:Animals; D004305:Dose-Response Relationship, Drug; D005260:Female; D007306:Insecticides / Q000633:toxicity*; D008294:Malathion / Q000031:analogs & derivatives* / Q000633:toxicity*; D008297:Male; D009374:Neoplasms, Experimental / Q000139:chemically induced* / Q000473:pathology; D051381:Rats; D011916:Rats, Inbred F344
D007306:Insecticides; C100082:malaoxon; D008294:Malathion