Stem-Like Cancer Cells
Cancer stem cells (CSC) are functional rather than having a fixed definition. The least stringent definition would be that the prospectively purified CSC population is more tumorigenic than the bulk or the marker-negative tumor cell population(s) in a suitable tumor development assay. Using the most stringent definition, a cancer stem cell should be a cell that, at the single-cell level, can reconstitute, in a recipient animal, a tumor that is identical to the parental patient tumor and that can be serially xenotransplanted indefinitely. Therefore, in a strict sense, none of the CSC thus far reported can be truly classified as CSC and should more appropriately be called tumor-reinitiating cells. In reality, it will be very difficult to identify a tumorigenic cell that can fulfill the most stringent definition of a cancer...