Features of tumor enhancement by croton oil.

Summary Because of the possibility of cocarcinogenic effects of substances to which many people are exposed, the mechanism of action of one such agent was examined in 2-stage tumor induction experiments. The appearance of new tumors was studied at the end of a series of croton oil treatments, or between treatments given at long intervals in mouse epidermis given a single pretreatment with a carcinogen. During a series of treatments with croton oil, the tumor-enhancing effect of any single treatment persisted for 2 to 3 weeks. Tumors were enhanced by as few as 2 croton oil treatments when given 3 weeks apart, and it was also demonstrated that the concentration of croton oil was more important in tumor enhancement than the absolute amount.