PREVENTION
The
PREVENTION of cancer, as of any disease, depends on the knowledge available about its causes and natural
history. The majority of human cancer, perhaps 80 or even 90 percent, is related to the environment, and thus identification and elimination or control of these environmental factors would seem to be the most logical approach to cancer
prevention.
The testing of substances on bacteria (the Ames test) and
animals are two widely used methods for discovering cancer-causing agents. The Ames test, which rapidly measures the ability of a substance to cause mutations in bacteria, is more than 90 percent effective in identifying potential carcinogens, which then may be tested in animals. Animal testing is tedious and expensive, but it is the only way to be certain that a particular agent is a carcinogen.
The prevention of human cancer associated with virus infectionsÑespecially those cancers associated with the Epstein-Barr and hepatitis-B virusesÑby means of vaccination is theoretically possible but has not yet been developed on any significant scale. Human cancer related to exposure to X rays, gamma rays, and other high-energy radiation is now relatively uncommon, largely as a result of federal controls.
Cancer-causing environmental factors are probably related most closely to the promotion stage of the natural history of cancer. Lung cancer is caused by continued and prolonged exposure to cigarette smoke. Dietary factors such as calories, fat, salt, fiber, alcohol, and other components are thought to cause as much as 30% of human cancers in the United States.