A carcinogenesis bioassay of cytembena, a cytostatic agent, was conducted by injecting intraperitoneally 7 or 14 mg/kg into groups of 50 male and 50 female F344 rats and 12 or 24 mg/kg into groups of 50 male or 50 female B6C3F1 mice three times per week for 104 weeks. Groups of 50 rats and 50 mice of both sexes served as vehicle controls.
Mean body weights of dosed and vehicle-control rats were comparable throughout the bioassay. Mean body weights of dosed and vehicle-control mice were comparable for the first 73 weeks of the bioassay; mean body weight of the high dose male mice was slightly lower than that of the vehicle controls after 73 weeks, and that of the high-dose female mice was lower after week 87.
In dosed male rats, mesotheliomas in the tunica vaginalis and malignant mesotheliomas in multiple organs occurred with dose-related trends and at incidences in each of the dosed groups which were significantly higher than those in the vehicle control rats.
In dosed female rats, fibroadenomas in the mammary gland occurred with a dose-related trend and at a significantly higher incidence in the high-dose group than in vehicle control rats.
Under the conditions of this bioassay, cytembena was carcinogenic for male and female F344 rats, causing increased incidences of mesotheliomas in the tunica vaginalis and in multiple organs of males and fibroadenomas in the mammary gland of females. Cytembena was not carcinogenic for male or female B6C3F1 mice.