Skin pigment cancer threat revealed

Fair people are more likely to develop melanoma

Scientists may have worked out why malignant melanoma is much tougher to treat than other types of skin cancer.

Melanoma arises in a type of skin cell called a melanocyte - dark coloured cells which give skin its pigment.

People with darker skin have more melanocytes, and tend to be less likely to develop skin cancer.

However, although the presence of a layer of melanocytes actually protects the skin from cancer-causing sunlight, once cancer starts in them, their natural defences may not work in the patient's favour.

Skin cancers amount for a large proportion of all cancers diagnosed in the UK.

However, only a relatively small number of these are melanomas, and most of the others are relatively easy to treat.

Melanoma accounts for as many as four in five skin cancer deaths.

Hard to beat

Conventional treatments have far less effect on melanomas than on other skin cancer types.

Scientists, writing in the journal Cell, now say this is because melanocytes have a defence mechanism that enables it to survive the constant bombardment of UV radiation which they endure on the skin's surface.

A gene, called MITF, found in these cells, halts a natural process killing cells which show signs of damage.

This appears to be the "master gene", turning on other genes to produce chemicals which ensure the cell's survival.

Cell death

Traditional chemotherapy and radiotherapy aim to cause enough damage to trigger this cell death process, called apoptosis.

In the case of the melanocytes - and the melanoma - the cells were simply ignoring the damage and ploughing on regardless.

Dr David Fisher, one of the scientists at the Dana-Farber Cancer Institute at Harvard University in the US, said: "While such a connection between pigmentation and survival is probably beneficial for normal pigment cell function, the flip side is that is may confer super survival properties and impede successful therapy in melanoma."

The researchers said that in theory, drugs which blocked the action of this gene might make a melanoma far more vulnerable to treatment, although no experiments to check this have been carried out so far.