Cancer is a disease in which cells multiply without con...
未知题型Cancer is a disease in which cells multiply without control, destroy healthy tissue, and endanger life. About 100 kinds of cancer attack human beings. The disease is a leading cause of death in many countries. In the United States and Canada, only diseases of the heart and blood vessels kill more people. Cancer occurs in most species of animals and in many kinds of plants, as well as in human beings.
2. Cancer strikes people of all ages but especially middle-aged persons and the elderly. It occurs about equally among people of both sexes. The disease can attack any part of the body and may spread to other parts. However, the parts most often affected are the skin, the digestive organs, the lungs, the male prostate, and the female breasts.
3. Scientists do not know exactly why cancer develops. Most experts agree that people develop cancer mainly through repeated or prolonged contact with one or more cancer-causing agents, called carcinogens. These agents include the tars in tobacco smoke, a variety of other chemicals, and certain kinds of radiation. In many cases, cancer can be prevented if a known agent is avoided or eliminated. The elimination of cigarette smoking, for example, would prevent most cases of lung cancer and about a third of all cases of cancer. Scientists also believe that some people may inherit a tendency to develop cancer.
4. Without proper treatment, most kinds of cancer are fatal. Only a doctor can diagnose cancer. But in many cases, a doctor is consulted only after the disease is far advanced. A person should therefore be alert to any physical change that may be a symptom of cancer. Early detection greatly increases the chances of a cure.
5. Cancer shows no symptoms in its beginning stages. But symptoms may appear before the disease spreads. The American Cancer Society lists seven such warning signals. They are: (1) Change in bowel or bladder habits; (2) A sore that does not heal; (3) Unusual bleeding or discharge; (4) Thickening or lump in breast or elsewhere; (5) Indigestion or difficulty in swallowing; (6) Obvious change in wart or mole; (7) Nagging cough or hoarseness. A person who has any of these symptoms longer than two weeks should consult a physician promptly.
