Evidence that weak promotion of carcinogen-initiated cells prevents their progression to malignancy.

Repeated promotion of 7,12-dimethylbenz[alpha]anthracene-initiated cells in mouse skin with 12-O-tetradecanoylphorbol-13-acetate (TPA) induces them to grow as premalignant skin papillomas and some of these subsequently progress to carcinomas. In this study, we demonstrate that this TPA-induced progression of initiated cells to papillomas and carcinomas could be prevented by exposing them previously to weak promoting regimens or to agents that mimic TPA activity.