"Cancer is the name given to a collection of related diseases. In all types of cancer, some of the body’s cells begin to divide without stopping and spread into surrounding tissues. Cancer can start almost anywhere in the human body, which is made up of trillions of cells. Normally, human cells grow and divide to form new cells as the body needs them. When cells grow old or become damaged, they die, and new cells take their place. When cancer develops, however, this orderly process breaks down. As cells become more and more abnormal, old or damaged cells survive when they should die, and new cells form when they are not needed. These extra cells can divide without stopping and may form growths called tumors. Cancerous tumors are malignant, which means they can spread into, or invade, nearby tissues. In addition, as these tumors grow, some cancer cells can break off and travel to distant places in the body through the blood or the lymph system and form new tumors far from the original tumor. Unlike malignant tumors, benign tumors do not spread into, or invade, nearby tissues. Benign tumors can sometimes be quite large, however. When removed, they usually don’t grow back, whereas malignant tumors sometimes do. Unlike most benign tumors elsewhere in the body, benign brain tumors can be life threatening. Neoplasms are clusters of abnormal cells, also called tumors. When neoplasms or tumors grow out and replace normal cells, they are said to be infiltrating or metastasizing, which means traveling to other parts of the body via the blood or lymph. Carcinoma is the most common form and starts in the epithelium. Sarcoma forms in connective tissue, including bones, muscles, and blood vessels. Leukemias form in blood-forming tissues, including bone marrow, lymph nodes, and the spleen. Lymphomas form in the cells of the lymph system, the system that filters out impurities and/or infection. Conceptually, cancer is thought to develop via the turning on of genes called oncogenes, or genes that have gone awry. The DNA in these cells replicates at an accelerated rate. Tumor suppressor genes, which are present in all of us, fail to stop these cells from dividing, thereby allowing a tumor to form. A malignant tumor is a cancerous tumor, whereas a benign tumor is not cancerous and of no imminent danger to the body."