阅读理解
One genetic mutation(基因突变)occurs on average for every 15 cigarettes that a typical lung-cancer patient smokes, according to a study that has found for the first time all of the mutations happen during the lifetime of a cancer patient．
Scientists have completed a full genetic examinations of the genomes(基因组)of cancer patients, and hope the information will lead to a basic understanding of the causes of cancer－and possibly drugs and treatments－by making out the mutations that turn a healthy cell into a cancerous tumor cell．
They studied a lung-cancer patient who had about 23,000 DNA mutations in his lung cells that were connected with exposure(暴露)to the toxins found in cigarette smoke and had built up over his lifetime．
They also looked at a patient with malignant melanoma(恶性黑色肿瘤), the most dangerous form of skin cancer, who had got 30,000 special mutations known to be connected with exposure to sunlight．
Scientists believe this new finding into the genetics of cancer will finally lead to new drugs and perfect treatments that aim at the specific changes to the gene that cause the disease, as well as new techniques for discovering following cancers that have escaped from treatment in other parts of the body．
“For the first time, we have a complete map of all mutations in a cancer cell,” said Dr．Peter Campbell, who led the Cancer Genome project to work out the whole DNA system of tumor cells in order find the mutations．
A similar method was performed on the cells of a patient with skin cancer, which is how the researchers were able to show that the malignant skin cells contained changes that resulted from exposure to light．
“These are the two main cancers in the developed world for which we know the chief exposure．For lung cancer it is cigarette smoke, and for malignant melanoma it is exposure to sunlight,” Professor Campbell said．
特高级教师点拨系列答案
