英语流行话题听力:Unit 16 什么是癌症?

Unit 16
　　What Is Cancer?
　　As you probably know from the appeals being made for funds to fight cancer, and from all the research that is being down on this subject -- cancer is a great threat to the health and life of mankind. We will only discuss cancer in general terms, so you can have a general idea of what happens in a body that has cancer.
　　A cancer is a continuous growth in the body which does not follow the normal growth pattern. The cells forming the cancer spread through the body to parts which may be far from the spot where the cancer began. Unless it is removed or destroyed, the cancer can lead to the death of the person.
　　Cells in the body are growing all the time. As they wear out and disappear, their places are taken by new cells of exactly the same kind. But cancer cells look and act differently from normal body cells. They look like the young cells of the part of the body where they started -- but different enough to be recognized as cancer when seen through a microscope.
　　When these cancer cells divide and increase in number, they don't change into the fully grown form and then stop reproducing. Instead, they remain young cells and continue to increase in number until they are harmful.
　　As cancer cells grow, they do not remain in one spot, but separate and move in among the normal cells. They may become so numerous that the normal cells in this part of the body cannot continue to work or even remain alive. When the cancer gets into the blood, it is carried to distant parts of the body. There it may grow to form large masses which interfere with the activities of the normal cells.
　　Unless the growth and spread of the cancer is stopped, the patient will die. That is why it is important to have periodic examinations to detect and treat cancer before it has spread too far.
　　Cancers are not spread from man to man by contact. No drug has been found that cures completely and is useful for all kinds of cancer. One of medicine's greatest goals is to understand fully the nature and cause of cancer, and to find a way to prevent and cure it.