"What Is Cancer?\n\n293 Figure 8. Cancerous Cells 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 in to 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 cel ls 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 witho ut stopping and may form growths called tumors. C ancerous 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. Key Cancer Terms • Neoplasms : clusters of abnormal cells; aka “tumors.” When the neoplasms or tumors grow out and repl ace 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 : most common form; starts in the epithelium. • Sarcoma : forms in connective tissue: bones, muscles, bloo d vessels."