Signatures of sunlight
In a landmark study, researchers have described the first comprehensive catalogue of somatic mutations in a cancer genome. The breadth and clarity of the view of the genome from a patient with malignant melanoma is matched only by a companion study on lung cancer, published in the same issue of Nature.
The melanoma genome contains more than 33,000 mutations, many of which bear the imprint of the most common cause of melanoma - exposure to ultraviolet (UV) light. But the comprehensive catalogue of mutation reveals other more unusual mutations and many not related to exposure to UV light.
Malignant melanoma is responsible for three out of four skin cancer deaths: most forms of skin cancer are relatively treatable, especially if detected early.
"This is an unprecedented view of a cancer genome. Written within this code is the history of this cancer - its mutations from UV light and the mutations it acquired when it spread within the patient. We have revealed the archaeology of exposure in this cancer genome, which becomes a palimpsest of successive mutations."
Professor Michael Stratton, from the Cancer Genome Project at the Wellcome Trust Sanger Institute
"It is amazing what you can see in these genomes. UV-light-induced mutations leave a typical signature, forming the vast majority of the mutations."
"Indeed because of the clarity of the genome data, we can distinguish some of the early, UV-induced mutations from the later mutations that do not have this signature, presumably occurring after the cancer cells spread from the skin to deeper tissues."
Dr Peter Campbell from the Wellcome Trust Sanger Institute
The sequence also shows the genome's attempts to protect itself from damage, with DNA repair systems most active in gene regions, whereas the regions between genes are left less well guarded. Even with these actions, 182 changes in genes that would impair their function were charted.
"Within the lists of disrupted genes are all those that have driven the original cell to this malignant state. We know that this cancer sample has a mutation in BRAF and other genes already implicated in melanoma. To discern all the important changes, we will need to analyse more samples."
Dr Andy Futreal, from the Cancer Genome Project at the Wellcome Trust Sanger Institute
The genomes - cancer cell and normal cell - were sequenced more than 70 times over to produce accurate data.
The project was led by researchers from the Wellcome Trust Sanger Institute. In 2002, this group discovered that a mutation in one gene called BRAF was important in driving development of melanoma. That discovery has already driven the development of novel therapies that are in clinical trials.
Notes and statistics
Malignant melanomas are the least common types of skin cancer, but the most serious. There are around 10,000 new cases each year in the UK, around 60,000 in Europe and around 54,000 in the USA.