We investigated the effect of in vitro and in vivo environments on the growth behavior of two stable, related rat tracheal squamous cell carcinoma lines while controlling for cell selection. One line was transplanted as tumors in syngeneic hosts for 2 years of continuous passage, and the other was derived from an early tumor passage and maintained continuously in cell culture, The in vitro cell cycle kinetics and doubling time of cells from the transplanted tumor line were identical to those of the long-term-cultured cell line and, when implanted into syngeneic hosts, the cultured cell line gave rise to tumors with growth behavior that was the same as that of the transplanted tumors. The differences in the cell cycle kinetics and growth parameters of the cells in the solid tumors and of the same cells in culture can be explained on the basis of differences in their environments. Selection for different populations of cells when the cells are transferred between environments is unlikely. The comparability of the populations in each of the two environments supports the validity of tests on cells isolated from solid tumors, as long as the cells are simply transferred between the environments and are not allowed to undergo selection during passage in the new environment.

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Supported by Contract N01 CP 3361 from the National Cancer Institute and Grant 1 T32 ES07088-01 from the National Institute of Environmental Health Sciences.

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