[Last Updated: Wednesday, 20 December 2006, 00:04 GMT
Secrets of skin cancer fightback
The deadliest form of skin cancer appears to cheat chemotherapy by disguising itself as a normal cell.
Malignant melanoma kills more than 1,700 people each year in the UK, and can be hard to treat even with powerful anti-cancer medication.
Researchers found melanoma cells can change shape, spread around the body, then remain dormant for years before developing a new tumour.
The Marie Curie Research Institute study appears in Genes and Development.
The researchers said the discovery could help find new ways to halt the cancer.
Melanoma is a cancer of melanocytes, the pigment cells that help give skin its colour.
It is particularly dangerous compared with other types of cancer because it has the ability to spread to other parts of the body. Once this has happened, it becomes much harder to cure.
The Marie Curie research team, led by Dr Colin Goding, believe they have found one of the reasons why melanoma is so good at getting around the body.
He noticed that under certain conditions, cancer cells in the original tumour can change shape and stop dividing rapidly - taking on the appearance of a normal skin pigment cell.
This has a double effect, with the new round shape making it easier for the cell to leave the tumour and squeeze through small gaps to find new places to grow, while at the same time reducing the value of chemotherapy, which targets only abnormal, fast-dividing cells,
Dr Goding said: "These invasive cancer cells develop in response to conditions inside the tumour.
Treatments possible
"Once they have spread into other areas of the body, their new environment determines whether they remain dormant, or whether they start dividing again to form new tumours."
Importantly, the researchers believe they have uncovered how the cell manages to transform itself.
The level of a cell chemical called 'Mitf' appears to play a role - if it falls, melanoma cells stop dividing and change shape, creating the conditions for the cancer to start spreading.
The levels of Mitf appear to be governed by conditions within the tumour.
Dr Goding suggests that it might be possible in future to create treatments which prevent this cell change from taking place.
Another possibility might even be to raise Mitf levels during cancer treatment to 'flush out' cells which have remained undetected and make them vulnerable to chemotherapy.
Dr Goding said: "This work has important implications for understanding how melanoma progresses and spreads, and how we treat it." However, there is no treatment based on Mitf that is likely to emerge quickly.
Tough to tackle
Consultant dermatologist Dr Charlotte Proby said that there were likely to be many factors aside from Mitf which governed the ability of melanoma to spread, or metastasise, around the body.
She said: "The problem is that once a melanoma has spread to other parts of the body, it becomes very difficult to treat.
"After five years, fewer than 10% of patients in this situation are alive.
"The main feature of melanoma that governs the likelihood of spread is the thickness of the initial tumour.
Thin melanomas - 1mm or less thick, are very treatable, while if the tumour is 4mm thick or more, it is much more likely that it will have metastasised."]
