Researchers in the United States have identified cancer stem cells which give rise to malignant skin tumours, sparking hopes of new treatment.

Malignant melanoma tumours can be fatal, and researchers at Stanford University have now identified 'master cells' which they say are responsible for the growth of the tumours.

The findings offer a new route for possible drug research and development, as well as explaining why some forms of malignant melanoma are hard to treat.

More than 10,000 people are diagnosed in the UK alone with melanoma, which is linked to exposure to too much ultraviolet light from the sun.

Doctors are seeing four times as many cases as they did 30 years ago, on the back of a boom in cheap overseas holidays and the use of tanning salons.

While 80% of tumours are diagnosed early and removed, lead Stanford University researcher Alexander Boiko said that conventional immunotherapy often missed the 'stem cells' associated with late-stage melanoma.

Treatment regimes that did not succeed in wiping out these newly discovered cells at the root of the cancer were doomed to failure, he said.

Cancer stem cells are a subset of cancer cells that lie at the root of many kinds of tumour, can make copies of themselves and differentiate into other cancer cell types.

Resistant to radiotherapy and chemotherapy, stem cells are often the reason why cancers return after treatment.

They have been found in tumours of the breast, colon, brain and bladder, but were first found in blood cancers.

Boiko, whose study was published in the journal Nature, said he was surprised to find such a clear-cut result which fitted in exactly with previous discoveries of cancer stem cells in other solid tumours.

The cells have the ability to renew themselves, and also to morph into other types of cancer cell.

Targeted treatments could stop the disease from recurring, according to cancer experts, who hailed the study as an important step towards beating melanoma.