Cancer is a very general word used to indicate many malignant diseases that may have only the vaguest relationship. Generally a cancer is an invasive group of cells that grow uncontrollably. Eventually cancer cells may spread into the territory of healthy cells critical to the operation of the body and kill or disable them. Cancers strike in many different ways; they react differently to medical treatment; and they have different growth patterns. They tend to have one grim characteristic in common, though: they usually kill. Taken together cancers have long been the second most common cause of death in America after heart disease. In 1950, 204,000 people died of cancer, accounting for about 14 percent of all deaths in the country.