Initiation-promotion versus complete skin carcinogenesis in mice: importance of dark basal keratinocytes (stem cells).

Tumor promotion research has accelerated at an explosive level during the past decade and continues to do so because of its importance to the understanding of the induction of human cancer. Furthermore, the promotion process, being mostly reversible allows one to find very effective ways to prevent cancer. The extensive data available as well as the multistage nature of tumor promotion suggests that this process, which is thought to occur in most tissues where cancer can be induced or occurs spontaneously, may involve the interaction of a number of environmental factors such as chemical, radiation, viruses and diet and nutrition, thus unifying all of the current areas of cancer research. In terms of human cancer, smoking, asbestos, radiation, alcohol and diet, and nutrition just to mention a few, are not thought to have more than a promotional influence in the carcinogenesis process. Here and in later papers we will discuss some important aspects of promotion as well as discuss the possible controversial nature of this process. In this review we present data which suggest that carcinogenesis can be operatively and mechanistically divided into various stages.