To understand cancer, it is helpful to know about normal cells and what happens when cells become cancerous. The body is made up of many types of cells. Normally, cells grow and divide to produce more cells only when the body needs them. This orderly process helps keep the body healthy. If the cells keep dividing when new cells are not needed, they form too much tissue.
Excess tissue can form a mass, called a tumor.
Excess tissue can be benign or malignant. Benign tissue is not cancer. The cells do not invade nearby tissue or spread to other parts of the body. Malignant tissue is cancer. The cancer cells divide out of control.