Causes and Risk Factors
Doctors don't know why some cells become leukemic cells and others don't. For most people who have chronic lymphocytic leukemia (CLL), there are no obvious reasons why they developed the disease. CLL has generally not been associated with any environmental or external risk factors with one exception (see "A Risk for Vietnam Veterans," below). Researchers have concluded that there's no way to prevent CLL.
You can't catch CLL from someone else. However, experts have found that in a small number of cases, first-degree relatives (parents and siblings) of people with CLL are three to four times more likely to develop CLL than people who don't have first-degree relatives with the disease. But the link isn't common, and the risk is small.
A Risk for Vietnam Veterans
Researchers have found a potential association between CLL and exposure to herbicides like Agent Orange used during the Vietnam conflict from 1961 to 1971. The U.S. Department of Veterans Affairs (VA) entitles those exposed to receive disability compensation. If you have CLL and think you may have been exposed to Agent Orange or other herbicides, you're entitled to benefits. The VA is urging Vietnam veterans to apply for compensation to begin processing their claims. For more information, visit the U.S. Department of Veterans Affairs website.
How Does CLL Develop?
CLL starts in a stem cell in the bone marrow. It can spread to other areas such as the central nervous system, the lymph nodes and, more rarely, the testes. Stem cells form blood cells (white cells, red cells and platelets.)
The stem cells that become white cells start out as blast cells called lymphoblasts, which produce lymphocytes, a type of white cell. There are three major types of lymphocytes:
- B lymphocytes, which produce antibodies to help combat infections
- T lymphocytes, which have several functions including assisting B lymphocytes to make antibodies
- natural killer (NK) cells, which can attack virus-infected cells or tumor cells
Ninety-five percent of CLL cases start in the B lymphocytes. In the remaining 5 percent of cases, the cell that transforms from normal to leukemic has features of T lymphocytes or NK cells.
CLL occurs when lymphoblasts grow out of control, leading to an increase in the number of CLL cells in the blood. These leukemic cells accumulate in the marrow and lymph nodes. Over time, CLL cells replace normal lymphocytes in the marrow and lymph nodes. If the marrow contains a high number of CLL cells, they may crowd out normal red cells, platelets and white cells. However, the CLL cells don't block production of normal cells as extensively as the leukemic cells do in people with acute lymphoblastic leukemia (ALL). That's why the early stages of CLL are generally not as severe as they are in ALL.
Two Different Forms of CLL
CLL can be slow growing and need no immediate treatment. Another form can grow at a faster rate, requiring treatment right away:
- The slower-growing form has an increased number of lymphocytes but a normal or slightly below normal level of red cells, platelets and neutrophils (another type of white cell) in the blood. This form can remain stable for years.
- The faster-growing form has too many CLL cells in the blood that block normal cell production. As a result, the number of fully functioning red cells and platelet levels drop lower than normal.
People with the faster-growing variety may have:
- Enlarged lymph nodes. The nodes can compress nearby organs, causing them to function improperly. For example, an enlarged node pressing on the stomach can interfere with gastrointestinal or urinary tract functions.
- A severe immunoglobulin deficiency. Immunoglobulins are proteins in the blood that fight infection. Low levels of immunoglobulins, sometimes combined with low neutrophil levels, can lead to recurrent infections.
- An enlarged spleen. The spleen can press on the stomach causing early fullness (satiety) while eating food and also discomfort in the left upper part of the abdomen.
If not treated, the faster-growing form of CLL can eventually lead to serious health conditions that affect the blood:
- anemia, or too few red cells to supply an adequate amount of oxygen
- neutropenia, or too few neutrophils, which impairs the body's ability to fight infections
- thrombocytopenia, or too few normal platelets, which causes easy bruising and bleeding