Cancers are caused by an accumulation of mutations that alter the activity of genes involved in controlling cell birth, growth, and death. Some of these errors are inherited. Most, however, occur after birth, triggered by cancer-causing agents in the environment or by mistakes that happen when cells divide. If the growth of cancer can be likened to a car speeding out of control, the mutations that cause the disease are the functional equivalent of cutting the brakes, gluing down the accelerator, or hiring an inept mechanic—or doing all three at once. Dr. Vogelstein explains that although there are numerous kinds of cancer, all stem from alterations that allow cell division to outstrip cell demise.