Phorbol as a possible systemic promoting agent for skin carcinogenesis.

UNLABELLED: In a repetition of a previous experiment, using this time a 20-fold higher dose of phorbol, administered i.p. as potential (systemic) promotor for skin carcinogenesis, 6/22 (27%) of the treated mice (after a single skin application of DMBA as initiator) developed papillomas, as compared to 1/20 (5%) in the DMBA control group. Though the difference is statistically no more than of borderline significance (P less than 0.05), it does raise the possibility that unesterified phorbol is, after all, a weak promotor for skin carcinogenesis. ABBREVIATIONS: DMBA equals 7,12-dimethylbenz(a)anthracene. TPA equals 12-0-tetradecanoyl-phorbol-13-acetate.