Selected cell and selective microenvironment in neoplastic development

Recent analysis of genetic alterations in human cancer points to a major ro le for selection in neoplastic development but provides few details about t he dynamics of the process. Many such details, however, have emerged from q uantitative studies of spontaneous transformation among mammalian cells in culture. The chief insight of these studies is that there is a continuous g eneration of variants in proliferative potential among growing cells that p rovides the substratum for progressive development to a frankly neoplastic state when selective growth conditions are persistently applied. Much of th e selection occurs before the cells are capable of producing discrete neopl astic foci. The varied observations in cell culture draw attention to analo gous features of carcinogenesis in experimental animals and the development of human cancer.