Improved tumour yields by means of a TPA-DMBA-TPA variation of the Berenrlum-Mottram experiment on the back skin of NMRI mice. The effect of stationary hyperplasia without inflammation.

Application of the phorbol ester TPA to the back skin of NMRI mice 14 times within a period of 7 weeks causes a stationary hyperplasia, with a corresponding increase in the labelling index of the basal cells from 1% to 14%. By initiation of skin, which has been pretreated with TPA in this way, with the carcinogen DMBA, followed by continued treatment with TPA (initiation-promotion corresponding to the classical Berenblum-Mottram experiment) the tumour yield (papillomas, carcinomas) is very much higher than that obtained using the scheme of the normal Berenblum-Mottram experiment. The preliminary induction of a stationary hyperplasia with high rates of nucleic acid synthesis must be considered an important co-factor in epidermal carcinogenesis.