Cancer - Description
Cancer is responsible for one out of every four deaths in the United States. It is second only to heart disease as a cause of death in this country. About 1.2 million Americans were diagnosed with cancer in 1998. Of that number, more than 500,000 are expected to die of the disease.
Cancer can attack anyone, but the chances of getting the disease increase with age. The most common forms of cancer are skin cancer, lung cancer, colon cancer, breast cancer (in women; see breast cancer entry), and prostate cancer (in men; see prostate cancer entry). Other major cancers that affect Americans include those of the kidneys, ovaries, uterus, pancreas, bladder, rectum, and blood and lymph nodes (see leukemia entry).
Cancer is a disorder that affects the genes. A gene is a small part of a deoxyribonucleic (pronounced dee-OK-see-RIE-bo-noo-KLEE-ik) acid (DNA) molecule. DNA molecules carry the master plan in cells that tells them how to behave. Genes carry the directions for making proteins. Proteins are involved in a wide number of functions in the body that make it possible to move, think, breathe, and carry out other activities.
Normally, cells go through a cycle in which they grow, divide, and die. Gene mutations (changes) can interrupt that cycle. Cells forget how to stop growing and reproduce over and over again, forming a lump of cells that gets bigger and bigger. The lump is known as a tumor or neoplasm ("new growth," pronounced NEE-o-plaz-um).
A healthy person's immune system can usually recognize and destroy neoplastic cells. Sometimes, though, mutant cells can escape detection. When they do, they can go on to become tumors. Tumors are of two types: benign ("harmless," pronounced bih-NINE) and malignant (harmful and possibly terminal, pronounced muh-LIG-nent). Benign tumors grow slowly and do not spread in the body. Once removed, they usually do not reappear. Malignant tumors, by contrast, invade surrounding tissue and spread through the body. If removed, a malignant tumor often grows back.
Most gene mutations are caused by environmental factors called carcinogens (pronounced car-SIN-o-genz). Carcinogens are things in our environment that cause cancer. Many kinds of carcinogens are known.
- A growth that does not spread to other parts of the body, making recovery likely with treatment.
- Surgical removal and microscopic examination of tissue for diagnostic purposes.
- Bone marrow:
- Spongy material that fills the center of bones, from which blood cells are produced.
- Any substance capable of causing cancer.
- Treatment of cancer that uses chemicals or drugs that destroy cancerous cells or tissues.
- The layer of cells covering the body's outer and inner surfaces.
- Hormone therapy:
- Treatment of cancer by slowing down the production of certain hormones.
- Treatment of cancer by stimulating the body's immune system.
- Cancer cells that have broken loose from a tumor and spread to other parts of the body.
- The process by which cancer cells have spread from their original source to other parts of the body.
- Radiation therapy:
- Treatment that uses various forms of radiation to kill cancer cells.
- An abnormal growth that has developed as cancer cells grow out of control.
- X rays:
- A kind of high-energy radiation that can be used to take pictures of the inside of the body, to diagnose cancer, or to kill cancer cells.
Some kinds of cancer are caused by genetic factors. Faulty genes can be passed from parents to children. When that happens, the children are at risk for cancer. In most such cases, a cancer is caused by some combination of genetic and environmental factors.
Normal body characteristics can increase the likelihood that a person will develop cancer. For example, people with fair skin are more likely to get skin cancer (see skin cancer entry) than those with darker skin.
Cancers can be classified according to the part of the body in which they occur:
- Carcinomas. Carcinomas (pronounced car-sen-O-muhz) are cancers that arise in the epithelium (pronounced eh-peh-THEE-lee-um). The epithelium is the layer of cells that covers the outside (the skin) and the inside of the body. Carcinomas covering the exterior epithelium are called squamous (pronounced SKWAY-muss) cell carcinomas. Those that develop in an organ or gland are called adenocarcinomas (pronounced add-en-o-car-sen-O-muhz).
- Melanomas. Melanomas are another form of skin cancer, and usually occur in cells that give skin their color (melanocytes).
- Sarcomas. Sarcomas are cancers of the supporting tissues of the body, such as bone, muscle, and blood vessels.
- Leukemias. Leukemias are cancers of the blood.
- Lymphomas. Lymphomas are cancers of the lymph system.
- Gliomas. Gliomas are cancers of nerve tissue.