Melanoma appears to defy cancer stem cell theory

In collaboration with the Press Association

US scientists have found evidence suggesting that the 'cancer stem cell' theory may not apply to melanoma - the most deadly form of skin cancer.

The theory that cancers develop from 'rogue' stem cells was put forward in 1997, when evidence for such 'cancer stem cells' was published in Nature Medicine. Scientists found that only a tiny proportion of cells taken from a given tumour had the ability to grow into new tumours when transplanted into laboratory animals.

Since then, stem-like cells have been found in many types of cancer, including breast, bowel and prostate cancer.

Further work on melanoma previously estimated that only about one in one million melanoma cells were able to grow into new tumours.

However, a new study by researchers at the University of Michigan, which appears as the cover article in Nature, has found that at least one quarter of melanoma cells have the ability to form new tumours.

When scientists updated and improved the laboratory tests used to detect cancer stem cells and applied them to human melanoma cells transplanted into mice, they found the cells to be quite common.

According to the researchers, the findings suggest that the stem cell model needs to be reassessed as it appears not to hold true in melanoma.

Ed Yong, Cancer Research UK's science information manager, said: "The idea that most types of tumour grow from a tiny population of 'cancer stem cells' is one of the most interesting ideas in current cancer research. But this study suggests that it may not be true for every type of cancer - in melanoma, a much larger proportion of cancer cells are able to give rise to a new tumour.

"This study shows how important it is that we continue to fund research into how cancers develop at a fundamental level."

Sean Morrison, director of the University Of Michigan's Centre for Stem Cell Biology, said that the test usually used to detect cancer stem cells "misses" most of them.

He commented: "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. The field will have to be reassessed after more time is spent to optimise the methods used to detect cancer stem cells."

Study co-author Dr Timothy Johnson, director of the university's Multidisciplinary Melanoma Programme, noted that the cancer stem cell model has been regarded by some people as an "exciting new source for the development of life-saving cures for advanced melanoma".

"Unfortunately, our results show that melanoma does not strictly follow this model," he revealed.

"So we'll need to redirect our scientific efforts and remain focussed on the fundamental biological processes underlying the growth of melanomas in humans. And as we pursue new treatments for advanced melanoma, we'll have to consider that a high proportion of cancer cells may need to be killed."

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