Carcinogenic and co-carcinogenic studies of thiram on mouse skin.

Thiram (tetramethyl thiuram disulfide), a carbamate fungicide, is used in the rubber processing industry as an accelerator and vulcanizing agent. Previous studies evaluated the tumorigenic potential of thiram in rodents, but failed to provide conclusive results. In the present study the tumorigenic potential of thiram was evaluated in Swiss albino mice by a two-stage initiation-promotion protocol and a long-term in vivo bioassay for carcinogenicity. Results revealed that following tumour initiation with thiram and promotion with 12-O-tetradecanoyl phorbol 13-acetate, skin tumours developed, mostly at the site of treatment (dorsal skin) in single and multiple dose-initiated animals. Similarly, papillomatous growths were observed on the dorsal skin of the mice initiated with a single subcarcinogenic dose of dimethylbenzanthracene and promoted with thiram. Thiram failed to provoke tumorigenesis when tested as a complete carcinogen for up to 52 wk and thereafter the study was terminated due to increased mortality. It is concluded that thiram has both tumour initiating and tumour-promoting potential in both sexes of Swiss albino mice following topical exposure at the tested dose level.