Nature has an interesting lead article this week on cancer stem cells. By modifying the assay used to calculate the prevalence of tumorigenic cells, these folks from Ann Arbor have shown that they can increase the yield of human melanoma stem cells from 0.1 - 0.0001% to ~25%. Subsequent testing revealed that CD133 in the high yield assay did not enrich for stem cells.
Significance: The assertion that tumorigenic cells are very rare and can be selected for by flow or other cell sorting methods is called into question, as the yield is so dependent on the model set up.
Food for thought.