Researchers at the Wellcome Trust Sanger Institute in the United Kingdom found over one hundred mutations associated with cancer in each square centimeter of the mammalian skin. They achieved this through ultra-deep genetic sequencing. The mutations were identified as having occurred over the course of a person's life due to exposure to the sun's rays.
The researchers say that the cells under observation merged into clusters they called "clones." These mutations are some of the first signs of cancer development. This video gives a synopsis of the findings of the Wellcome Trust Sanger Institute. It goes further to explain the methodology of their research and the implications of such findings.