Chemical carcinogenesis by the two-stage protocol in the skin Mastomys natalensis (Muridae) using topical initiation with 7,12-dimethylbenz(a)anthracene and topical promotion with 12-0-tetradecanoylphorbol-13-acetate.

The long-term (34 weeks) topical administration of 7,12-dimethylbenz(a)anthracene (DMBA) to the skin of male and female Mastomys induced a broad spectrum of benign and malignant tumors in all animals treated. In a two-stage carcinogenesis experiment with topical initiation with DMBA and topical promotion with TPA, 50% of the animals developed both benign and malignant skin tumors. In general, benign tumors occurred between weeks 15 and 25, whereas malignant tumors were seen 40 weeks after initiation. In contrast to the situation in Mus musculus, the benign tumors consisted mainly of keratoacanthomas instead of fibroepitheliomas. In the non-initiated, TPA-treated, control group four benign and four malignant tumors were seen, whereas animals of the DMBA-initiated, acetone-treated control group were free of tumors. The promotion of virus transformed cells with TPA is discussed.