Two-stage carcinogenesis in NMRI mice: intravaginal application of 7,12-dimethylbenz[a]anthracene as initiator followed by the phorbol ester 12-O-tetradecanoylphorbol-13-acetate as promoter.

In this study a new modification of the systemic 2-stage carcinogenesis experiment is described. Tumors were induced in NMRI-mice using a single intravaginal application of the carcinogen 7,12-dimethylbenz[a]anthracene (DMBA) (initiator) followed by intravaginal treatment with 12-O-tetradecanoylphorbol-13-acetate (TPA) (promotor) as a cocarcinogen over a period of 52 weeks. The substances were applied using small tampons. Development of preneoplastic lesions or neoplasias was not found in the group of untreated control animals (n = 50) and in TPA treated animals (n = 50). However, mice which had been treated with TPA alone showed pronounced hyperplasia. When DMBA was applied without subsequent treatment with TPA (n = 100), formation of preneoplastic lesions was frequently observed. Fibroepitheliomas (papillomas), carcinomas and sarcomas, typically located intravaginally and at the external region of the vagina, were observed after the combined treatment with DMBA and TPA (n = 100). In addition, benign as well as malignant tumors were found, mainly in the forestomach, in DMBA treated animals and more frequently after application of DMBA and TPA. Tumors of the lung and leukemias were identified more frequently in comparison to the normal spontaneous tumor rate in NMRI mice, and were probably in part caused by the promoting substance TPA. On the other hand, no significant tumor formation in the mammary gland and in the ovaries was observed after DMBA/TPA application. The tumors observed in these organs were, however, caused by treatment with the carcinogen DMBA only. This new modification of the 2-stage experiment, i.e. the direct intravaginal application of initiating and promoting substances, has special relevance for the elucidation of the mechanisms involved in the development of carcinomas located at the portio vaginalis uteri in humans.