Dichlorvos--a comprehensive review of 11 rodent carcinogenicity studies.

Dichlorvos (DDVP) has been studied in 11 cancer bioassays. Only two studies, the National Toxicology Program (NTP) rat and mouse studies, show any indication of carcinogenic effects and these results, an increase in mononuclear cell leukemia in the rat and an increase in forestomach tumors in the mouse, appear to be related to the corn oil vehicle. The increase in mononuclear cell leukemia was confined to the male rat, was not dose-related, did not show an earlier onset than the controls, had no effect on survival, was within the range seen in historical controls, and was not confirmed in five other rat studies, four of which used higher doses. The increase in forestomach tumors in mice in the NTP study, in which DDVP was administered by corn oil gavage, was confined to the highest dose, occurred against a high background of hyperplasia and forestomach tumors in the control mice, and was not confirmed in 10 other studies. Sustained irritation from daily gavaging with the corn oil vehicle, in conjunction with this high background, likely explains this response in the forestomach, which does not exist in humans. These 11 rodent studies provide strong evidence that DDVP is not carcinogenic.