Tumor progression in XXXX and its representation in cell culture.

@entity19 @entity54964 @entity5 @entity665
Varying dilutions containing from 10(6) to 10(3) spontaneously transformed Balb/3T3 cells were inoculated into @entity19 [N:NIH( @entity54964 ]. Less than half the @entity19 inoculated with 10(3) cells developed @entity5 . The higher concentrations of cells produced visible @entity5 in all @entity19 within 2-3 weeks, and these @entity5 grew rapidly to large sizes. Some @entity5 initiated by the lower concentrations of cells arose quickly, but others were greatly delayed in onset, then grew slowly, if at all, for several weeks before a rapid acceleration. The delayed acceleration can be considered a form of @entity5 progression. When first explanted into culture, cells from the early @entity5 multiplied somewhat more slowly than the parental cells that initiated the @entity5 , but narrowed the gap in a few weekly passages. By contrast, only a small fraction (less than or equal to 0.001) of cells from the longest delayed @entity5 could sustain multiplication in culture, although flow cytometry revealed them to have been a rapidly multiplying population when explanted. A relatively large fraction of these explanted @entity5 cells incorporated a 1-hour pulse of @entity665 into DNA, although at a low rate. The shift to culture apparently slowed progress through the S-period of the cell cycle. The multiplication rate of cell populations from the delayed @entity5 increased in successive passages in culture. There was great heterogeneity in growth capacity among clones of the @entity5 cells. The growth rates of some clones declined to the point of extinction, those of others remained constant for several weeks, while those of still others steadily increased in growth rate. The low initial cloning efficiency of cells from the delayed @entity5 and the heterogeneity of growth rates among the clonable cells indicate that selection plays a major role in the increase of the growth capacity of the cell population. The steady increase in growth rates within clones suggests that physiological adaptation also contributes to the progressive growth of the @entity5 populations in culture. The results constitute a rationale for using the progressive growth of cells in culture as a model system for discriminating the types of cellular changes that underlie @entity5 progression.
