Chronic lymphocytic leukemia is one of the most common forms of leukemia in adults. About 15,340 people in the United States will develop CLL this year. The average age at diagnosis is 72, and the disease is twice as common in men as women.
How CLL Develops
Like other blood cells, lymphocytes evolve from immature cells called hematopoietic stem cells. Stem cells are produced in the bone marrow and usually mature, or differentiate, into one of a range of different kinds of blood cells. Lymphocytic stem cells mature into T lymphocytes (T cells), B lymphocytes (B cells), or natural killer (NK) cells. Each of these blood cell types has a specialized role in the immune system. Normal, healthy lymphocytes evolve through their life cycle in an orderly way and eventually die, to be replaced by new cells.
In CLL, changes in the diseased cells (most often B cells, but in rare cases T cells) prevent them from maturing properly, and while they may appear normal under a microscope, they are unable to perform their immune system functions. Because these cells have lost their ability to mature, they have a much longer lifespan than normal lymphocytes. Over time large numbers of these faulty cells accumulate in the bone marrow and in the tissues of the lymphatic system, displacing normal red and white blood cells and platelets and interfering with other immune system functions.
