Scientists discover melanoma stem cells

In the world of cancer research, there's growing evidence for cancer stem cells - rogue stem cells that fuel the growth of tumours. When they divide, cancer stem cells produce new stem cells as well as so-called 'bulk' tumour cells. Treatments like radiotherapy and chemotherapy kill off the bulk cells, but don't touch the stem cells, so they carry on growing and the cancer returns.  Stem cells have been found in many types of cancer, including breast and bowel cancer, and leukaemia. And now researchers at Stanford University School of Medicine in the US have found them in melanoma - the most dangerous form of skin cancer. Their research was published this week in the journal Nature.

Led by Alexander Boiko, the researchers were studying the protein molecules on the surface of cells taken from melanoma samples. They found that between 2.5 and 41 per cent of cells had a protein called CD271 on their surface. Using a technique called flow cytometry, they were able to separate out cells carrying this protein, and test their properties.

The researchers  transplanted human melanoma cells into mice, comparing cells that carried CD271 with cells lacking the protein. They discovered that cells with CD271 were much more likely to grow into tumours than cells without the protein, suggesting they may have stem cell-like properties.

Here's the clever bit - when the researchers analysed cells from tumours grown from the CD271-positive cells, they found a mixture of human cells - some carried the protein, while others didn't. This told them that the CD271 cells were not only making more stem cells, but making bulk tumour cells too - a classic giveaway of stem cell behaviour.

The discovery of these stem cells helps to explain why many melanomas don't respond to immunotherapy - a treatment that harnesses the patient's immune system to destroy cancer cells. The team discovered that the melanoma stem cells lacked certain proteins that are targeted by current immunotherapy approaches, so the body's immune system can't recognise and kill them, and the cancer comes back.

But now we know that the stem cells do carry CD271, researchers can start working on treatments that target that CD271, or other proteins that are specific to the stem cells. This could lead to powerful new treatments for melanoma that are so urgently needed.