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This is the VOA Special English Health Report.

Scientists have discovered a genetic change that can cause malignant melanoma, the most serious kind of skin cancer. The cancer then spreads through the body. Malignant melanoma kills almost forty-thousand people around the world each year.

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The new research was reported in the publication Nature. The work was done by medical scientists involved in the Cancer Genome Project at the Wellcome Trust Sanger Institute in Cambridge, England. The aim of the Cancer Genome Project is to find which of the thirty-thousand human genes are involved in cancer.

Genes contain material called D-N-A. The order of the D-N-A in a gene is represented by a series of letters. A change, or mutation, happens when the order of the letters changes. Mutations happen in two ways. Chemicals, radiation or viruses can damage D-N-A. Damage also can result from mistakes before cells divide.

Most of these mutations are harmless. However, sometimes a mutation in a gene will cause cells to act in an unusual way. For example, a changed gene will cause a cell to divide when it should stop dividing. Or the cell will move away from its normal place and into another organ. This is how cancer begins. Experts say it takes about twenty-five years from the time of the first gene mutation until a cancerous growth appears in adults.

Cancer Genome Project researchers have been examining human genes to find the abnormal genes that cause cells to become cancerous. The change that causes malignant melanoma is the first one they have found. It is in the gene called B-R-A-F, one of a group of genes that must all be turned on for a cell to grow and divide.

Scientists say when a gene causes a cell to grow and divide it is "turned on." Normally, it then "turns off" and stops the cell from dividing any more. The Genome Project scientists found that the mutation makes the gene stay turned on all the time. It causes the cells to divide and never stop. This leads to cancer.

The researchers say the finding could lead to effective drugs to treat melanoma. They have already started searching for drugs to make the gene turn off and stop the growth of the cancer. But they also say that people should try to prevent malignant melanoma from developing by staying out of the sun as much as possible.

This VOA Special English Health Report was written by Nancy Steinbach.