What Is Cancer?

Every organ in the body is made up of billions of cells. There are many different kinds of cells—heart muscle cells, liver cells, nerve cells, etc—each with a special job to do. New cells are constantly needed to replace those that get worn out or damaged. To produce these new cells, existing cells divide so that 1 cell produces 2 cells.4 How the body controls this process is not completely understood. Besides producing new cells, the body also controls the death of old cells by a process called apoptosis. Normally, these processes are orderly and predictable.

In cancer, cell division and cell death are out of control. Cells keep dividing and old cells do not die as they should. In solid tissues, these cells grow to form a small tumor that steadily increases in size. In leukemia, cancer cells take over the bone marrow and gradually crowd out normal cells in the blood. In lymphoma, a type of blood cell called a lymphocyte forms solid tumors in the lymphatic tissues.4

Cell division and cell death are controlled by the genetic information encoded in our DNA. This is the chemical that carries all the instructions for a living thing to grow and function. Every cell carries a full set of these instructions on structures called chromosomes, found in the cell nucleus. DNA copies itself every time a cell divides so that each new cell contains a full set of instructions.4

Occasionally, there is a mistake when DNA is copied, resulting in a cell that does not work properly. This is called a mutation. If this mutation involves the set of instructions that controls how the cell divides or dies, the cell may become cancerous and continue to multiply even when it should not or it may not "remember" to die.4

However, not all abnormal cell growths are cancers. Tumors that are not growing or spreading are called benign and are usually much easier to treat. Growing cancer cells have properties that make them difficult to treat.4:

Close Window