British scientists have identified a gene involved in the deadliest form of skin cancer, in one of the first successes to emerge from the mapping of the human genome.
They found that a gene involved in controlling cell growth was mutated in about 70 percent of malignant melanomas, skin cancers that affect more than 60,000 people in the UK and U.S. alone.
"This discovery is important because it highlights the genetics of melanomas, but also because it opens up a window that we hope to explore for potentially developing a new therapeutic drug," said Dr Andy Futreal, joint leader of the Wellcome Trust's Cancer Genome Project at the Sanger Institute, near Cambridge.
The discovery, published online by the science journal Nature, is the first fruit of the trust's Cancer Genome Project, the world's largest study of genes involved in cancer.
Cancer is the disease that lends itself best to an analysis of the human genome because all cancers are a disease of DNA, said Mike Stratton, head of the Cancer Genome Project, which aims to identify which of the 30,000 human genes are involved in cancer and how.
Genes are made up of a DNA code, represented by a sequence of letters. A mutation occurs when the order of the letters changes.
Mutations can be acquired in two ways: either when DNA is damaged by such toxins as radiation, chemicals or viruses, or when mistakes are made before cell division.
Each cell in the body contains a copy of the genome, and duplicates it before it divides into two. The copy isn't always perfect.
Most of the mutations are harmless. However, sometimes a mutation will occur in a particular cell in a key gene and the result will be that the gene will be either switched on or switched off.
That cell will then start to behave abnormally. It will divide when it should stop dividing. It will move out of its usual position in a tissue and may even float off into the bloodstream and deposit in another organ.
That is how cancer evolves. Experts estimate it takes about 25 years from the first gene mutation for a tumor to appear in an adult.
"With the human DNA sequence now available to us, we have started the lengthy and daunting task of trawling through the vast tracts of genome, gene by gene, to see if we can find the abnormal genes that drive cells to behave as cancers," said Futreal.
The gene, called B-RAF, shares much of its structure with another cancer-related gene called ABL, mutations of which are found in many leukemias, or cancers of white blood cells. A drug inhibiting the function of the ABL protein has had marked success in treating chronic myeloid leukemia.
The researchers found that the code letters in the B-RAF gene were shuffled in 70 percent of melanoma cases, making it the most frequently messed up gene in melanoma.
"We are very positive about this because B-RAF and ABL ... are part of the same family of proteins. They have the same biological function," Sanger Center director Mike Stratton said.
"If you can find a molecule that inhibits activity in ABL, it is very plausible to find a molecule that inhibits activity in B-RAF."
But he stressed that although scientists in Cambridge had already begun screening small molecules for B-RAF inhibiting activity, the findings provided only an avenue for research, not a definite cure.
"We have to temper our optimism with a certain amount of caution," Stratton said. "Cancers are devious beasts. They are unpredictable, and they do not always respond in the way we would like them to."