Cancer is the uncontrolled growth of cells in any part of the body. Cancer cells crowd out normal tissue and have the potential to spread throughout the body. All of them have a different biologic behavior meaning how slow or fast they grow, how aggressively they invade into tissue, and how likely they are to spread. Grade describes how abnormal the cancer cells appear under the microscope; low(er) grade tumors usually carry a better prognosis. Stage refers to how far the cancer has spread in the body.