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Lymphocytes are a type of white blood cells that help fight infections.

This type of leukemia usually progresses slowly, hence the term “chronic”.

First-degree relatives of individuals with CLL have an increased risk of developing the disease, emphasizing the role of genetics.

Genetic factors play a role in the development of CLL – deCODEme calculates your genetic risk on the basis of the best scientific data available

CLL is a cancer of the blood and bone marrow

Chronic lymphocytic leukemia (CLL, also called chronic lymphoblastic leukemia) is a form of cancer affecting a subgroup of white blood cells called lymphocytes, which are produced in the bone marrow. Lymphocytes, along with other white blood cells, have a special role in protecting the body from infections caused by germs such as bacteria and viruses. They are programmed to divide and multiply when they come into contact with foreign antigens found on germs, and to help rid the body of the infectious agents.

CLL reduces the infection-fighting ability of blood

Normally, the bone marrow produces different types of blood cells, which are released into the blood stream as needed. When blood cells die, the bone marrow replaces them with new ones. This continuous cycle becomes disturbed in people who have Chronic Lymphocytic Leukemia (CLL). The bone marrow starts producing abnormal lymphocyte cells that are unable to fight infections, but multiply in number. As these cancerous cells build up in the blood and bone marrow, often over long periods of time, the body has relatively fewer healthy lymphocytes. This reduces the overall ability of blood cells to fight infection. The proliferation of abnormal lymphocytes in the blood and bone marrow also affects other types of blood cells, causing symptoms such as anemia (due to fewer red blood cells) and an increased tendency for bleeding (due to fewer platelets).

CLL typically progresses at a slower rate than other leukemias

Symptoms of Chronic Lymphocytic Leukemia (CLL) can include anemia, fatigue, weight-loss, night-sweats, and enlarged lymph nodes. In many cases however, people with CLL can be symptom-free for years or even decades. A more serious and symptomatic disease develops if cancerous lymphocyte cells in the blood start invading other parts of the body, such as the lymph nodes, bone marrow, liver, or spleen.

CLL most commonly affects older adults

The average lifetime risk of getting CLL is about 0.5%, or 1 in 200. With an average age at diagnosis of around 70 years, Chronic Lymphocytic Leukemia (CLL) is mostly diagnosed in people over the age of 50, rarely in people under the age of 40, and is extremely rare in children. For unknown reasons, CLL is more often diagnosed in men than women.

Genetic variants found to increase risk of CLL

Six genetic variants, on chromosomes 2, 6, 11, 15 and 19, have been associated with increased risk of developing CLL. The deCODEme Complete Scan identifies these variants and provides an interpretation of the associated risk of CLL for individuals of European descent. At the current time, risk information for other ethnicities is not available for these variants.

Other risk factors for CLL

There are no proven controllable risk factors for Chronic Lymphocytic Leukemia (CLL). The risk of developing this type of cancer does not seem to be affected by smoking, diet, exposure to radiation, or infections.

The main factors linked to an increased risk of developing CLL are:

• Age. The average age at diagnosis of CLL is around 70 years. It is rarely diagnosed in people under age 40, and is extremely rare in children.
• Gender. CLL is more common in males than females, although the reasons for this are not known.
• Race/Ethnicity. CLL is more common in North America and Europe than in Asia. Most experts think this reflects genetic differences between these groups rather than environmental factors as people maintain the same risk even when they move from one area to another.
• Family history. A person's risk of developing CLL may be higher than average when there is a family history of this disease or other blood and bone-marrow cancers. First-degree relatives of individuals with CLL have a two-to-four-fold increased risk of developing CLL.
• Exposure to certain chemicals is thought to increase risk of CLL, such as Agent Orange, an herbicide used by the U.S. military during the Vietnam War. Other studies have suggested that long-term exposure to certain other pesticides may also increase the risk of developing CLL. However, more research is needed to determine the impact of chemical agents on CLL risk.

Early detection can delay CLL symptom progression

There are currently no recognized controllable risk factors for Chronic Lymphocytic Leukemia (CLL). As there is no proven way to prevent this type of cancer, early detection provides physicians with the opportunity to monitor the disease progression closely and intervene appropriately as soon as symptoms develop.

Although CLL can be found on routine blood-tests (for example if a person's white blood cell count is unusually high), the American Cancer Society does not presently recommend routine screening for CLL.

Treatment options for people with CLL vary greatly, depending on the type of CLL, the disease stage, and whether or not the disease causes harmful symptoms. In symptom-free patients, treatment may not be necessary.

As CLL can be a symptom-free disease for a long time and treatment may cause side effects, doctors often advise watchful waiting upon initial diagnosis. Watchful waiting does not reduce the effectiveness of future treatment should it become necessary.

More Information about Chronic Lymphocytic Leukemia (CLL)

• American Cancer Society. What is CLL?
• Mayo Clinic, Tools for Healthier Lives
• National Cancer Institute on Leukemias
• National Cancer Institute on CLL

Scientific references

1. Di Bernardo MC, Crowther-Swanepoel D, Broderick P, et al. (2008). A genome-wide association study identifies six susceptibility loci for chronic lymphocytic leukemia. Nature Genetics, Oct;40(10):1204-10. Epub 2008 Aug 31.
2. Crowther-Swanepoel D, Broderick P, Di Bernardo MC, et al. (2010). Common variants at 2q37.3, 8q24.21, 15q21.3 and 16q24.1 influence chronic lymphocytic leukemia risk. Nature Genetics, Jan 10. [Epub ahead of print].

This content was last reviewed on February 08, 2010.

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