Genetic background and development of skin tumors.

Inbred mouse strains that differing widely in their susceptibility to multistage skin carcinogenesis provide useful models for studying the genetic factors involved and advancing our understanding of the biochemical and molecular events associated with this process. The process of skin tumor initiation appears to be somewhat similar in various strains of mice, and most data in the literature suggest that differences in response to skin tumor promoters are a major determinant in controlling susceptibility to multistage skin carcinogenesis. A model system has been developed for examining the genetics of susceptibility to skin tumor promotion. The susceptibility to phorbol ester skin tumor promotion in crosses between DBA/2 and C57BL/6 mice is inherited as an incomplete dominant trait, and neither X-chromosome nor cytoplasmic genetic determinants appear to play a major role in determining susceptibility in these two inbred strains. In addition, two or more genetic loci contribute to the higher sensitivity of DBA/2 mice than C57BL/6 mice to TPA-induced skin tumor promotion. Further studies to characterize these genes will contribute greatly to our understanding of the mechanisms of phorbol ester skin tumor promotion. In addition, much work should now be directed at understanding the cellular, biochemical, and molecular mechanisms for differential responsiveness not only to phorbol esters but also to other classes of tumor promoters.