Cancer is not just one disease but many diseases. In fact, there are more than one hundred different types of cancer. A cancer, or malignant neoplasm, starts when abnormal cells in a particular part of the body begin out-of-control growth. The growth of cancer cells differs from the growth of normal cells. Cancer cells do not die, but continue to grow and invade and destroy other tissues.
Normal cells become cancer cells when there is damage to the cell's DNA. All cancer begins in the cells - the building blocks of life. DNA controls the actions of each cell. When the DNA in a normal cell becomes damaged, the cell either dies or repairs the damage. In a cancer cell, the damaged DNA isn't repaired and the cell does not die. The cancel cell then proceeds to reproduce and make new cells, all with the same damaged DNA.
While cells with damaged DNA can be inherited, this is not common. Most DNA damage is caused by environmental factors.
Generally, cancer cells replicate and form a tumor. Sometimes, though, cancer infects the blood and circulates through the body to other sites where they continue to grow.
TYPES OF CANCER
Cancer types are generally grouped into the following major categories, depending upon the type of cell in which the tumor originates:
Carcinoma - A cancer that begins in epithelial cells in the skin or in tissues that line or cover internal organs. Examples of carcinomas include breast, prostate, lung and colon cancer.
Sarcoma - A cancer that begins mesenchymal cells, or cells in bone, cartilage, fat, muscle, blood vessels, or other connective or supportive tissue.
Leukemia - A cancer that starts in blood-forming tissue such as the bone marrow and causes large numbers of abnormal blood, or hematopoietic, cells to be produced and enter the blood.
Lymphoma and Myeloma - Cancers that begin in the cells of the immune system.
Germ Cell Tumors - Cancers that derive from pluripotent cells, such as the testicles and ovaries.
Blastoma - Cancer that is derived from what is known as "precursor," or embryonic, tissue.
Central Nervous System Cancers - Cancers that begin in the tissues of the brain and spinal cord.
CAUSES OF CANCER
The causes of cancer are divided into two groups:
Cancer is considered to be primarily an environmental disease. although genetics may influence the degree to which a person is at risk from cancer, there are many common environmental factors the may contribute to the formation of cancer. These factors include environmental pollutants, certain hormones, ionizing radiation, aging, sunlight, some viruses and bacteria, tobacco (whether chewed or smoked), poor diet, obestity, and alcohol.
Cell reproduction is regulated by several gene classes, such as oncogenes and tumor suppressor genes. Any abnormalities in these genes, whether by heredity or environment, can lead to the development of cancer. Cancers that are entirely hereditary make up only five to ten percent of all cancers.
In 1971 President Nixon introduced the "war on cancer." Since that time the U.S. has invested hundreds of billions of dollars in cancer research. Leading cancer research organizations include the American Association for Cancer Research, the American Cancer Society (ACS), the American Society of Clinical Oncology, the European Organisation for Research and Treatment of Cancer, the National Cancer Institute, and the National Comprehensive Cancer Network.
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