{{B}}Cancer{{/B}}
1. Cancer is a group of many related diseases that begin in cells, the body's basic building blocks. The body is made up of many types of cells. Normally, cells grow and divide to produce more cells as they are needed to keep the body healthy. Sometimes, this orderly process goes wrong, New cells form when the body does not need them, and old cells do not die when they should. The extra cells form a mass of tissue called a growth or tumor (肿瘤). Benign (良性的) tumors are not cancer. They can often be removed and, in most cases, they do not come back. Malignant (恶性的) tumors are cancer. Cells in malignant tumors are abnormal and divide without control or order.
2. Scientists have learned that cancer is caused by changes in genes that normally control the growth and death of cells. Certain lifestyle and environmental factors can change some normal genes into genes that allow the growth of cancer. Many gene changes that lead to cancer are the result of tobacco use, diet, exposure to ultraviolet (紫外线的) radiation from the sun, or exposure to carcinogens (致症物) in the workplace or in the environment. Some gene alterations are inherited.
3. Cancer treatment can include surgery, radiation therapy, chemotherapy (化疗), hormone therapy, and biological therapy. The doctor may use one method or a combination of methods, depending on the type and location of the cancer, whether the disease has spread, the patient's age and general health, and other factors. Because treatment for cancer can also damage healthy ceils and tissues, it often causes side effects. Patients and doctors generally discuss the treatment options, weighing the likely benefits of killing cancer cells and the risks of possible side effects.
4. Having cancer does not always mean having pain. Whether a patient has pain may depend on the type of cancer, the extent of the disease, and the patient's tolerance for pain. Most pain occurs when the cancer grows and presses against bones, organs, or nerves. Pain may also be a side effect of treatment. However, pain can generally be relieved or reduced with prescription medicines or over-the-counter drugs recommended by the doctor.