Co-carcinogenicity of promoting agents.

An experiment is described to investigate whether coadministration of a promoting agent would enhance the carcinogenicity of a repeatedly administered complete carcinogen. Topical application of the strong carcinogen 15,16-dihydro-11-methylcyclopenta[a]phenanthren-17-one (I) in toluene containing 1% v/v croton oil is about five times more effective than applications in toluene alone, as judged from the respective mean latent periods. A similar effect is also apparent for benzo[a]pyrene.