Our body is made up of cells. All cancers begin in cells, which are the fundamental unit of life. To understand cancer, it's useful to know what happens when normal cells become cancer cells.
The body is composed of a variety of cells. These different types of cells grow in a well-controlled, steady manner to produce more cells that keep the body growing and functioning normally. As cells age or are damaged, they die and are replaced. But if this normal pattern is interrupted, then there will be an abnormal reaction from the cells. This reaction will come from one area or organ of the body where the cells continue to multiply and live beyond their life span. These cells are the cancerous cells.