Forestomach lesions in rats and mice administered 3-chloro-2-methylpropene by gavage for two years.

The carcinogenicity of 3-chloro-2-methylpropene (CMP), a chemical intermediate and insecticide, was studied because of possible human exposure and because of its structural relationship to vinyl chloride and allyl chloride. CMP in corn oil was administered by gavage to groups of 50 male and 50 female Fischer 344/N rats at 0, 75, or 150 mg/kg body weight and to groups of 50 male and 50 female B6C3F1 mice at 0, 100, or 200 mg/kg body weight, 5 times a week for 103 weeks. The body weights of the two CMP treated groups of rats were 3-15% lower than the controls; the survival rates were similar. The body weights and survival rates of the CMP-exposed male and female mice were not different from the respective controls throughout the study. CMP administration resulted in dose-related increases in the incidence and severity of forestomach basal cell hyperplasia and the incidence of forestomach squamous cell papillomas in both sexes of rats and mice. In the two groups of CMP-exposed male mice the incidences of squamous cell carcinoma of the forestomach were also increased. Invasion or metastasis of the squamous cell carcinomas to other organs was observed in 2 male mice treated at 100 mg/kg and in 3 male mice and one female mouse treated at 200 mg/kg. The data show that CMP is a carcinogen for the forestomach in rats and mice and acts at the tissue site of contact and support genetic toxicity findings that CMP is a direct-acting alkylating agent.