LONDON: Researchers have discovered the one-in-ten-billion genetic mutation which causes death from the severest form of skin cancer — malignant melanoma.

The discovery is the first success for the world’s most ambitious effort to decode the genetic alterations which lead to cancer, the Cancer Genome Project, based at the Welcome Trust Sanger Institute in Hinxton near Cambridge, UK.

Work has begun on a drug to halt the effects of the mutation. The researchers say it could begin clinical trials in five years.

Melanoma affects about 6,000 Britons each year, killing more than a quarter of them. Melanoma accounts for only 11 per cent of skin cancers but almost all the deaths from skin cancer.

The Sanger Institute team found that in 70 per cent of melanoma tumours, there are mutations in a single gene, Braf, which governs cell growth. Some 80 per cent of these mutations involve a change in just one of the three billion-plus “letters” which make up the human genetic code, or genome.

All cancers are genetic in origin, because tumours cannot grow until a series of genetic safety catches are flipped to “off” and a series of genetic switches are flipped to “on.” But that does not mean they are inherited. The genes can be switched on and off by environmental factors and by copying errors made naturally when cells divide.

“The most exciting thing about this discovery is that it could be a direct lead to new treatments for malignant melanoma,” said Professor Mike Stratton, head of the Cancer Genome Project.

Project scientists are optimistic about a Braf-targeted drug because the target is similar to that of an existing drug, Glivec, which has been effective in treating another cancer, chronic myeloid leukemia.

Four out of five cases of skin cancer are caused by excessive exposure to the sun. Other risk factors are fair skin, large numbers of moles (50 to 100) on the body and age — the 40 to 60 age group is most affected. The incidence of melanoma is increasing more rapidly in men than in women. If untreated the cancer cells can spread to other parts of the body, such as the brain, lung or liver.

Prof Stratton’s team have compiled the world’s largest collection of cancer cell lines — about 1,500 in all — and are comparing the genes in them with the genes in the human genome project data, searching for what makes cancer cells genetically different.—Dawn/The Guardian News Service.