On the role of croton oil in tumor formation.

The ability of croton oil to elicit epithelial tu mors in mice in areas previously treated with subcarcinogenic amounts of carcinogenic hydrocar bons is a well documented fact. In the typical ex periment tumors are initiated in the skin of mice by the single application of a solution of some car cinogenic hydrocarbon at a level that induces few if any tumors. The repeated application of croton oil to such skin will quickly elicit tumors, while the same schedule of croton oil applied to similar mice not previously treated with carcinogen has been regarded to be without effect (2, 5, 8). Experiments are described in this paper show ing that croton oil can be an effective agent for the production of both papillomas and carcinomas without the aid of a small dose of carcinogenic hydrocarbon. A preliminary report of these ob servations has been made (12), while more recent ly Roe and Salaman reported a high incidence of tumors in control groups of mice treated with croton oil only (10, 11), Selye observed sarcomas in rats given repeated injections of croton oil (16), and Berenblum and Harán found that mice fed croton oil developed papillomas of the forestomach (4).