Inactivity of two noble metals as carcinogens.

Silver and gold were evaluated for potential carcinogenicity by suspending fine (-300 mesh) powders in trioctanoin and injecting these intramuscularly in Fischer-344 rats. As a positive control, cadmium powder was tested; the vehicle alone served as the negative control. Under the conditions of these experiments, no tumors appeared at the site of injection in the silver-treated animals. Vehicle control (trioctanoin) and gold-treated groups each developed a single fibrosarcoma. In contrast, 60% of the cadmium-treated rats developed fibrosarcomas at the injection site. The mean survival time for the cadmium injected group was 16.5 months, whereas for all other groups it was approximately 23.5 months. It is concluded that the noble metals, silver and gold, are not carcinogenic under the conditions reported here.