How to estimate cancer stem cell frequency correctly

Cancer stem cell research is a focus for more and more cancer biologists and evidence of involvement in cancer development is becoming more abundant. Earlier studies indicated cancer stem cells to be rare as determined by the standard xenotransplantation assay using SCID mice in vivo. However, recent studies have shown that syngeneic transplantation of mouse tumors or modifications to the xenotransplantation assay can effectively improve the accuracy of detection, with stem cells being more abundant than hitherto thought. Furthermore, to estimate frequency correctly, it is necessary to considerate cancer stem cell subsets with differing capacities for tumorigenesis.