Tumor metastasis is not due to adaptation of cells to a new organ environment.

Murine B16 melanoma cells were adapted for lung survival and growth by allowing them to attach to Bio-Carrier beads and injecting the beads intravenously into normal mice. The beads lodged mechanically in the microcirculation of the lung. When the melanoma cells had grown into visible tumors from the arrested beads, the tumors were removed and the cells were dispersed, cultured to remove normal cells, and reattached to new beads. The process was repeated nine times. Previously another B16 subline was injected intravenously as a suspension of separate tumor cells. Those cells that survived and colonized the lungs were harvested, cultured, and injected again. This selection process was also repeated nine times. Only the subline that was injected in suspension was more metastatic than the parental line, indicating that metastasis involves selection of preexistent metastatic cells and is not an adaptive process by which all cells gradually acquire the ability to grow at particular organ sites.