Chronic lymphocytic leukemia (CLL)

What is chronic lymphocytic leukemia (CLL)?

Chronic lymphocytic leukemia (CLL) is a type of blood cancer that begins in the bone marrow. “Chronic” means that the leukemia is typically slower growing. Other things you should know about CLL:

• CLL is the most common type of leukemia in adults in Western countries 
• CLL patients have a number of effective treatment options available to them
• For low-risk (slow-growing) CLL, watch and wait  or active surveillance may be an appropriate treatment approach
• Many people with CLL live good-quality lives for years with medical care

Find facts and statistics for CLL and other blood cancers. 

What should I do if I am diagnosed with CLL?

• Choose a doctor who specializes in treating CLL, known as a hematologist-oncologist. Your local cancer specialist can also work with a leukemia specialist. Learn how to choose a blood cancer specialist or treatment center.  
• Talk with your doctor about your diagnostic tests and what the results mean.
• Talk with your doctor about all your treatment options and the results you can expect from treatment.
• Ask your doctor whether a clinical trial is a good treatment option for you.
• Obtain and keep records of your test results and the treatment you receive as this information is useful for long-term follow-up of your condition. Find out how. 

Learn more about communicating with your blood care specialist or find a list of suggested questions to ask your healthcare providers. 

How does CLL develop? 

CLL begins in the bone marrow. Bone marrow is located inside the bones and produces white blood cells called lymphocytes that fight infection. CLL starts with a mutation (change) to a B cell, also called B lymphocytes, a type of white blood cell. This abnormal cell is a leukemia or a CLL cell.  

This damaged stem cell becomes a leukemic cell and multiplies into many CLL cells. The CLL cells grow and survive better than normal cells. As a result, the number of healthy blood cells is usually lower than normal, and can result in the following conditions: 

• Anemia: a condition when there is a low number of red cells in the blood, which can cause fatigue and shortness of breath
• Neutropenia: a condition when there is a low number of white cells, which means the immune system can't effectively guard against infection due to a lack of neutrophils (a type of white cell)
• Thrombocytopenia: a condition when there is a low number of platelets, which can cause bleeding and easy bruising with no apparent cause
• Pancytopenia: occurs when there are low numbers of all three blood cells  

CLL doesn't completely interfere with the development of mature red cells, white cells, and platelets. Therefore, it is generally less severe than acute leukemia. Some people with CLL have no symptoms when they are first diagnosed by a routine blood test.  

View a 3D model of CLL’s impact on the body. Click or tap the "Interact in 3D" button to begin. 

What are risk factors for CLL?

Doctors don't know why some cells become leukemic cells and others don't. For most people who have CLL, there are no obvious reasons why they developed the disease, there are no known ways to prevent CLL, and you can’t catch it from someone else. 

 The following have been identified as risk factors for CLL:  

• Some studies have associated exposure to Agent Orange, an herbicide used during the Vietnam War, with an increased risk of CLL. For more information, visit the VA website.
• Some studies suggest that exposure to benzene in the workplace increases the risk of CLL
• Genetic factors likely play a role in the development of CLL, as some families have more than one family member with the disease
• CLL generally affects older people and more males than females 

CLL with increased prolymphocytes (CLL-PL) or prolymphocytic leukemia 

About 15 percent of people with CLL have leukemia cells that are a mix of lymphocytes and another type of white blood cell, called a “prolymphocyte.” Most people with this type of CLL follow a similar disease course to that of typical CLL. However, for a relatively small group of patients with this type of CLL, their blood cells may become mainly composed of prolymphocytes, the spleen may enlarge further, and the disease may become more aggressive and less responsive to treatment. In these cases, patients are encouraged to talk to their doctors about participating in a clinical trial.

Learn about clinical trials. 

Source: Chronic Lymphocytic Leukemia: In Detail Reviewed by  Mazie Tsang, MD, MAS, MS.