By
Edward R. Winstead

June 21, 2002

cientists have identified a gene that is commonly mutated in malignant melanoma, the deadliest form of skin cancer. The discovery was made during the first phase of the British Cancer Genome Project—an effort to discover genetic mutations involved in cancer by systematically analyzing the human genome sequence.

The gene, called BRAF, is mutated in 70 percent of malignant melanomas and less frequently in other cancers. Most of the BRAF mutations involve a change in a single letter of DNA, which prevents the gene from switching on and off normally. Malignant melanoma accounts for only about ten percent of skin cancers, but almost all of the deaths.

All cancers are the result of genetic mutations that accumulate over the course of a person's lifetime. The BRAF gene was among the first twenty genes analyzed by the Cancer Genome Project, because it is related to cancer susceptibility genes involved in controlling the growth of cells. The researchers will continue to analyze the 30,000 or so genes in the draft human genome sequence on a gene-by-gene basis.

The source of the mutations in BRAF is not known, but they are not inherited. Nor do they appear to be caused by too much exposure to sunlight, which is the main environmental risk factor for skin cancer. The BRAF mutations in this study differ from those caused by ultraviolet light, according to the findings published online in Nature.

The researchers discovered the mutations by comparing cancerous cells to normal cells donated by the same patients. After screening an initial group of fifteen patients, they analyzed the BRAF gene in tumor cells from hundreds of skin cancer patients and found an unusually high percentage of mutations. Mutations were also present in cells from patients with lung and colon cancer.

Richard Wooster led the research at the Wellcome Trust Sanger Institute near Cambridge, England. He and Michael R. Stratton, a colleague at The Institute of Cancer Research in London, started the Cancer Genome Project a few years ago as a spin-off of the publicly funded international Human Genome Project.

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Davies, H. et al. Mutations of the BRAF gene in human cancer. Nature. Published online June 9, 2002.

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