Quarter of skin cells 'on road to cancer'

More than a quarter of a middle-aged person's skin may have already made the first steps towards cancer, a study suggests.

Analysis of samples from 55- to 73-year-olds found more than 100 DNA mutations linked to cancer in every 1 sq cm (0.1 sq in) of skin.

The team, at the Sanger Institute, near Cambridge, said the results were "surprising".

Experts said prevention was the best defence against damage from the sun.

Skin cancer is one of the most common cancers.

Ultraviolet-radiation from sunlight bombards our skin and transforms it from healthy to cancerous tissue. 

Many of the mutations that culminate in skin cancer are already known, but the team wanted to know when they first started to appear.

The researchers analysed excess skin that had been removed from the eyelids of four patients.

They then drilled down deeply into the skin's DNA to discover the very first steps being taken on the journey to cancer.

Dr Peter Campbell, the head of cancer genetics at Sanger, told the BBC News website: "The most surprising thing is just the scale, that a quarter to a third of cells had these cancerous mutations is way higher than we'd expect, but these cells are functioning normally."

However, it would take multiple mutations - nobody is sure exactly how many - to culminate in a tumour.

The results, published in the journal Science, did show there were some subtle changes in the way the mildly mutated cells were behaving.

They were growing more quickly than other skin cells.