Diazepam inhibition of phorbol ester tumor promotion.

Diazepam (Valium) had previously been shown to enhance the growth rate of some transplantable tumors although studies in other systems have suggested an inhibitory effect. Skin tumor promotion studies were therefore carried out to determine the effect of diazepam on 12-O-tetradecanoyl phorbol-13-acetate (TPA) promotion in SENCAR mice. A sex-independent dose response inhibition occurred over a dose range of 100 g to 5 mg, both in number of papillomas and percent of mice bearing tumors. Furthermore, a dose-response reduction in tumor size was observed. By itself, diazepam had no tumor promoting activity.