This is Sarah Long. And this is Bob Doughty with SCIENCE IN THE NEWS, a VOA Special English program about recent developments in Science. Today, we tell about the disease cancer. We tell about the different kinds of cancer. We tell about how doctors treat the disease. And we tell the seven warning signs of cancer.

Many diseases cause fear in people. But one disease seems to be the most feared, although it has been recognized for hundreds of years. That disease is cancer. Although the word is simple, the disease is not.

Cancer in humans takes more than one-hundred different forms. All of the forms of cancer attack the body in different ways. However, they are called cancers because they are similar in what they do.

Generally, cancer is a disease in which cells change, divide and produce more cells without control or order. All tissues and organs of the body are made of cells. Normally, cells divide to produce more cells only when the body needs them. This orderly process helps keep us healthy.

Cancer appears when the body's complex chemical system becomes damaged and cells begin reproducing or dividing without control. If cells keep dividing when new cells are not needed, a mass of tissue forms. This mass of extra tissue, called a growth or tumor, can be benign or malignant.

Benign tumors are not cancer. Usually they can be removed. Generally they do not return or form again. Cells from benign tumors do not spread to other parts of the body. Such tumors rarely are a threat to life.

Malignant tumors are cancer. They can threaten the life of a person if they are not treated. Cancer cells from such tumors can invade and damage nearby tissues and organs. Also, cancer cells can separate from a malignant tumor and enter the bloodstream or the body's lymphatic system. This is how cancer spreads from one tumor to form new tumors in other parts of the body. The spread of cancer is called metastasis.

The structure of cells in malignant tumors is not normal. All normal cells in the body have special purposes that help the body operate. Cancer cells have no purpose other than to reproduce and spread. And all organs and tissues can be threatened by cancer. Cancerous tissue, growing without limits, competes with normal tissue for nutrients. In time, the cancer cells kill normal cells by taking all the nutrients. The normal cells starve.

Cancerous tissue has another effect as well. A growing tumor creates pressure against the nearby organs and surrounding tissue. This pressure can interfere with the operation of the organs, slowing the normal processes of the body. Signs of this kind of pressure are weakness, weight loss, and a lack of interest in food.

The parts of the body that are most often affected by cancer are the skin, the lungs, the prostate gland in males, the breasts in females and the digestive organs. These organs include the throat, stomach, large and small intestines and colon. Cancer in these organs is most common among older people. Generally, men and women are affected equally by most kinds of cancer.

Without proper treatment, most kinds of cancer cause death. For centuries, there have been many efforts to treat the different forms of cancer, but with little success. In the late part of the twentieth century, methods of discovering and treating cancer greatly improved. Generally, about one-half of all cancer patients now survive for at least five years after medical treatment. This is mainly because early discovery of the disease means there is an increased chance of successful treatment.

Cancer can be found in several ways. The first method is by looking closely. Another way is to feel for tumors. The most common example of this is to search for lumps or abnormal growths in a woman's breast. The use of X-rays is another common method of finding tumors.

Doctors perform an operation called a biopsy if they suspect that cancer is present in an organ. This involves removing some of the tissue and studying the cells with a microscope.

The most common form of treating cancer is by operating. Cancer surgery involves removing the tumor and repairing affected organs. Doctors generally try to remove some tissue surrounding a tumor in an effort to protect against the possibility that cancer cells have spread.

Another treatment for cancer is radiation. The radiation rays are used to damage cancer cells and stop them from growing and dividing. Radiation affects cancer cells only in the treated area. There are two methods of using radiation to treat cancer. One involves using a machine to aim the radiation at the cancerous part of the body.

The other radiation treatment involves an operation to place radioactive material inside the body, near the tumor or cancerous tissue.

Chemotherapy is another method of treating cancer. This involves the use of chemicals or drugs designed to kill cancer cells. The drugs flow through the bloodstream to all parts of the body. Most often the drugs are injected into the body or are taken through the mouth. Another method in chemotherapy treatment is to pump anti-cancer drugs into the body through a thin tube called a catheter.

Chemotherapy is generally used for short periods. It is halted for a recovery period. Sometimes chemotherapy can make a patient very sick, requiring a stay in the hospital. However, most chemotherapy patients can receive the treatments at a doctor's office, the hospital, or even at home.

Sometimes, doctors use the body's natural defense system to fight cancer. This kind of treatment is called biological therapy, or immunotherapy. The body already has a system designed to protect itself from infection and diseases. Biological therapy involves efforts to expand the effectiveness of the defense system to attack cancer cells and expel them from the body.

These cancer treatments often produce what are known as side effects. Side effects can include tiredness, stomach sickness, little or no desire for food, hair loss, weight gain, high body temperature, muscle pain and weakness. Doctors are usually able to help patients deal with many of these side effects until they disappear after the treatment is completed.

Doctors do not know all the causes of cancer. But they do know some of them. The material asbestos is one of them. People have been using asbestos for many centuries. However, scientists discovered that asbestos caused lung and colon cancer in people who breathed small particles of the material. Another clear cause of lung cancer is smoking tobacco.

Sunlight is the chief cause of skin cancer, especially in people with light-colored skin. It is one of the most easily cured cancers, if it is treated early. X-rays and radioactive elements also are known to cause cancer.

Some cancers, such as breast cancer and stomach cancer, may be passed from parents to children. Doctors say that people whose parents had these diseases should be examined at least once a year for signs of cancer. However, most people who develop cancer are not born with cancer-causing genes. Instead, their genes have been damaged by substances in the environment.

Doctors say people should watch for the seven warning signs of cancer. The first warning sign is a change in how often a person passes waste materials. The second sign is a break in the skin, or sore, that does not heal. The third sign is unusual bleeding or leaking of body fluids. A thickening growth or lump in the breast or other part of the body is the fourth cancer warning sign.

The fifth warning sign is difficulty swallowing, or stomach problems. The sixth sign is a change in normal small growths or dark spots on the skin. The seventh cancer warning sign is a cough that does not go away, or a major change in the way a person sounds when talking.

A person with any of these cancer signs should seek advice from a doctor. Cancer often can be cured if it is found early.

This SCIENCE IN THE NEWS program was written by Oliver Chanler. It was produced by George Grow . This is Sarah Long. And this is Bob Doughty. Join us again next week for more news about science in Special English on the Voice of America.