It would be good for all of us if the cancer stem cell theory turns out to be true for even a majority of cancer types - as this would mean that a side-effect of stem cell research will be a cure for cancer. Unfortunately, there are good reasons to believe that this will not be the case; nothing in human biochemistry is as simple as we'd like. From EurekAlert!: "the cancer stem-cell model [must] be reassessed because it is based largely on evidence from a laboratory test that is surprisingly flawed when applied to some cancers ... I think the cancer stem-cell model will, in the end, hold up for some cancers. But other cancers, like melanoma, probably won't follow a cancer stem-cell model at all. ... Scientists previously estimated that only one in 1 million melanoma cells has the ability to run wild, exhibiting the kind of unchecked proliferation that leads to new tumors. These aggressive interlopers are the cancer stem cells, according to backers of the model. But after updating and improving the laboratory tests used to detect these aberrant cells, [researchers] determined that at least one-quarter of melanoma cells [have] the ability to form new tumors. ... The assay on which the field is based misses most of the cancer cells that can proliferate to form tumors. Our data suggest that it's not going to be possible to cure melanoma by targeting a small sub-population of cells."