All organs of the body are made of cells. Normally, these cells divide to produce more cells only when the body needs them. Cancer occurs when these cells become abnormal and keep dividing without control or order. Therefore, cancer can affect any organ in the body.
"Cancer" is composed of more than 100 different disease types. Some of the most common types of cancer are discussed under "Types of Cancer". Normal body cells grow, divide, and die in an orderly fashion. During the early years of a person's life, normal cells divide faster to allow the person to grow. After the person becomes an adult, most cells divide only to replace worn-out or dying cells or to repair injuries.
Because cancer cells continue to grow and divide, they are different from normal cells. Instead of dying, cancer cells outlive normal cells and keep forming new abnormal cells. Another difference between cancer cells and normal cells is that cancer cells can invade (grow into) other tissues. Being able to grow out of control and to invade other tissues makes a cell a cancer cell.
To learn more about some of these common cancer diseases, select the appropriate link.