Diaplacental initiation of NMRI mice with 7,12-dimethylbenz[a]anthracene during gestation days 6--20 and postnatal treatment of the F1-generation with the phorbol ester 12-O-tetradecanoylphorbol-13-acetate: tumor incidence in organs other than the skin.

The tumor spectrum and tumor incidence in organs other than the skin were investigated in the 12-O-tetradecanoylphorbol-13-acetate (TPA) treated F 1-generation of 13 groups of NMRI mice which had been initiated by a single intragastric dose of 7,12-dimethylbenz[a]anthracene during days 6, 8, and 10--20 of pregnancy. Promotion by topical application of TPA to the back skin was carried out twice per week 12 weeks after birth over a period of 26 weeks. The forestomach epithelium represented the only organ in which statistically significant 2-stage carcinogenesis could be demonstrated. A promotion effect could be seen in tumors of the Harderian gland, of the liver of male animals and on the development of both benign and malignant tumors of the lung in both sexes. Promotion treatment therefore led to an activation of initiated tumor cells in those organs in which a very sensitive, more or less narrowly spaced oncogenic determination period exists.