Cancer stem cells questioned

Cancer stem cells are a hot topic in science - the idea that tumours are fuelled by a small group of immortal cells, which are resistant to conventional treatments.  Cancer stem cells have been found in many different types of cancer, and some people believe they are at the root of all forms of the disease.

Now scientists in the US are challenging that assumption. Writing in the journal Nature, the researchers have found that melanoma, a dangerous form of skin cancer, doesn't follow the conventional stem cell model.  This contradicts previous reports suggesting that stem cells were fuelling melanoma.

The team, led by Sean Morrison, carried out experiments using human melanoma cells that had been transplanted into mice.  If the stem cell model holds true, you would expect only a tiny fraction of the transplanted cells to give rise to cancers in the mice, as scientists have calculated that around one in a million melanoma cells is a stem cell. But in fact the researchers found that tumour-forming cells were actually very common, but hadn't been picked up in standard stem cell tests. Using their improved tests, they showed that around a quarter of the melanoma cells had the capacity to grow new tumours.

The researchers themselves say that this doesn't mean a complete failure of the stem cell model, and it's likely that the model will hold true for at least some cancers.  But certainly it look like it doesn't hold for melanoma. And it means that cancer scientists may have to revisit experiments done with other cancer types using these new techniques, to confirm their findings.