Cancer is a group of many different diseases that have some important things in common.
Cancer affects our cells , the body's basic unit of life.
To understand cancer, it is helpful to know what happens when normal cells become cancerous. The body is made up of many types of cells. Normally, cells grow, divide, and produce more cells as they are needed to keep the body healthy. Sometimes, however, the process goes astray cells keep dividing when new cells are not needed. The mass of extra cells forms a growth or tumor .