A Genome-Wide Cancer Dependency Map Draft.
Cancer is a genetic disease, that is, it is caused by certain changes to genes that control the way our cells function, especially how they grow and divide. Genes carry the instructions to make proteins, which do much of the work in our cells. Certain gene changes can cause cells to evade normal growth controls and become cancer. Others result in the production of a misshapen, and therefore nonfunctional, form of a protein that normally repairs cellular damage. Genetic changes that promote cancer can be inherited from our parents if the changes are present in germ cells, which are the reproductive cells of the body (eggs and sperm). Such changes, called germline changes, are found in every cell of the offspring. Cancer-causing genetic changes can also be acquired during one’s lifetime, as the result of errors that occur as cells divide or from exposure to substances, such as certain chemicals in tobacco smoke, and radiation, such as ultraviolet rays from the sun, that damage DNA. Genetic changes that occur after conception are called somatic (or acquired) changes.
There are many different kinds of DNA changes. Some changes affect just one unit of DNA, called a nucleotide. One nucleotide may be replaced by another, or it may be missing entirely. Other changes involve larger stretches of DNA and may include rearrangements, deletions, or duplications of long stretches of DNA. Sometimes the changes are not in the actual sequence of DNA. In general, cancer cells have more genetic changes than normal cells. But each person’s cancer has a unique combination of genetic alterations. Some of these changes may be the result of cancer, rather than the cause. As the cancer continues to grow, additional changes will occur. Even within the same tumour, cancer cells may have different genetic changes. Scientists identify cancer-causing alterations by comparing the sequence of all the DNA in a cancer cell with that in normal cells, such as blood or saliva, and identifying differences. They also search for chemical marks on the DNA and assess gene expression. This type of research is called cancer genomics research. Credit: National Cancer Institute.
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