The disease is a leading cause of death in many countries. In North America 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.
Cancer strikes people of all ages but especially middle-aged persons and the elderly.
It occurs about equally among people of both sexes and can attack any part of the body. The parts most often affected are the skin, the digestive organs, the lungs, and the female breasts. Without proper treatment, most kinds of cancer are fatal. In the past, the methods of treatment gave patients little hope for recovery, but the methods of diagnosing and treating the disease have improved greatly since the 1950's. Today, about one-third of all persons treated for cancer recover completely or live much longer than they would have lived without treatment.