a change in the deoxyribonucleic acid (DNA) of a cell. Most mutations do not cause cancer, and a few may even be helpful. But all types of cancer are thought to be due to mutations that damage a cell’s DNA. Some cancer-related mutations can be inherited (passed on from a parent). This means that the person is born with the mutated DNA in all the body’s cells. But most mutations happen after the person is born. These are called somatic or acquired mutations. This type of mutation happens in one cell at a time, and only affects cells that arise from the single mutated cell. See also cancer susceptibility genes, deoxyribonucleic acid, gene, inherited mutation, somatic mutation.