Each year, nearly 1.4 million new cases of cancer are diagnosed in the United States, a figure that does not include the 900,000 cases of skin cancer diagnosed annually. There are more than 100 different varieties of cancer, which can be divided into six major categories. Carcinomas , the most common type of cancer, originate in tissues that cover a surface or line a cavity of the body. Sarcomas begin in tissue that connects, supports or surrounds other tissues and organs. Lymphomas are cancers of the lymph system, the circulatory system that bathes and cleanses the body's cells.
Leukemias involve blood-forming tissues and blood cells.
As their name indicates, brain tumors are cancers that begin in the brain, and skin cancers , including dangerous melanomas, originate in the skin. Cancers are considered metastatic if they spread via the blood or lymphatic system to other parts of the body to form secondary tumors. Cancer is caused by a series of mutations, or alterations, in genes that control cells' ability to grow and divide. The mutations cause cells to divide relentlessly or lose their normal ability to die. Despite the fact that the cancer mortality rate in the U.S. has risen steadily for the past 50 years, scientific advances appear to have begun to turn the tide.