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.
Risk factors for developing CLL can include inherited, or genetic, traits and exposure to cancer-causing agents in the environment. There is only a very small chance that a person who has one of the few known risk factors for CLL will develop the disease.
People who have a first-degree relative — a parent, child, or sibling — with CLL have a two- to four-fold increased risk of developing CLL. Most people who develop CLL, however, do not have a relative with the disease.
CLL may also be linked to exposure to Agent Orange, a chemical used widely during the Vietnam War. Researchers at the Institute of Medicine, an arm of the National Academy of Sciences, have found that veterans who served in Vietnam have a heightened risk of CLL. Agent Orange exposure is also associated with higher rates of lymphoma, multiple myeloma, and other medical conditions.
Scientists know that most cases of leukemia are associated with specific gene mutations, but in most cases, it is not clear what causes those mutations.
When CLL first develops, patients may not have any symptoms, and this phase may last for several years. CLL is often discovered when people with the disease have routine blood tests during a regular checkup.
With the passage of time, however, as the number of diseased cells increases and they start to interfere with the body’s normal functioning, symptoms may slowly develop. These symptoms can include:
- shortness of breath
- weight loss
- enlarged lymph nodes
- a feeling of fullness in the abdomen
- night sweats
- loss of appetite
- fatigue, lightheadedness, and dizziness
- recurrent infections of the skin and respiratory tract
These symptoms are also commonly associated with a wide range of other conditions and illnesses. If these problems persist, consult a physician.