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What is Chronic Lymphocytic Leukemia (CLL)?

Chronic lymphocytic leukemia (CLL) is a type of blood cancer that begins in the bone marrow and enters into the blood. CLL may also be referred to as chronic lymphoid leukemia. CLL is a blood cancer that begins from lymphoid cells, which can become B cells, T cells, and natural killer cells.1,2

Most forms of CLL are generally slower growing, and the cancerous cells of CLL may accumulate over a long period of time. Many people may not have symptoms until the cancerous cells multiply and spread to the lymph nodes, liver, or spleen. However, chronic leukemias can potentially be more difficult to treat than acute leukemias.1

How does chronic lymphocytic leukemia develop?

The cells that make up the blood, including white blood cells, red blood cells, and platelets, are made in the bone marrow. Each of the different blood cells has their own purpose. Red blood cells carry oxygen to the tissues, platelets help stop bleeding by creating clots, and white blood cells are the immune system’s primary defense and are critical for fighting infections.3,4

The bone marrow is the spongy center portion of bones. The bone marrow contains blood stem cells, which are immature cells that can become different types of cells in the body. The cells differentiate into myeloid cells or lymphoid cells. Lymphoid cells can become cells such as B cells, T cells, and natural killer cells.2-4 CLL is a blood cancer that begins from lymphoid cells, and there are two main kinds of CLL:

  • B-cell CLL
  • T-cell CLL5

More than 95% of people who have CLL have the B-cell form of the disease. B-cell and T-cell CLL can be further subtyped based on genetics. These different subtypes can mean the CLL disease may have different effects in different people diagnosed with CLL. A relatively small percentage of patients with B-cell leukemia have a specific subtype referred to as B-cell prolymphocytic leukemia. Another B-cell CLL is called hairy cell leukemia.6

T-cell leukemias can also be further classified as large granular lymphocytic leukemia, T-cell prolymphocytic leukemia, adult T-cell leukemia/lymphoma, and Sezary syndrome (a leukemic form of T-cell lymphoma). Some forms of these tend to be slower growing. However, T-cell prolymphocytic leukemia and certain subtypes of adult T-cell leukemia/lymphoma can grow and progress quickly.7

Who gets chronic lymphocytic leukemia (CLL)?

CLL is among the most common forms of leukemia in adults. CLL usually occurs in older adults, with the average age at diagnosis approximately 71 years of age. CLL rarely occurs in people younger than 40, and it occurs extremely rarely in children.1

What factors increase a person’s risk of developing chronic lymphocytic leukemia?

Risk factors are characteristics that can increase someone’s chances of developing a disease. Only a few risk factors for CLL are known, including:

  • Exposure to some chemicals, like pesticides and Agent Orange (a chemical used during the Vietnam War)
  • Family history of CLL
  • Being male (the risk is slightly higher in males than females)
  • Being from North America or Europe (the risk is higher than for those from Asia)1

What are the common symptoms of chronic lymphocytic leukemia (CLL)?

CLL may be diagnosed before the person experiences any symptoms when undergoing blood tests for other reasons. When people do experience symptoms, they may be vague or easily mistaken as being caused by other conditions. CLL can potentially cause symptoms, such as:

How is chronic lymphocytic leukemia staged (CLL)?

CLL may be classified as Stage 0, I, II, III, or IV. The stages may also be separated into low risk, intermediate risk, and high risk groupings when considering treatment options.1,2

What is the prognosis for chronic lymphocytic leukemia (CLL)?

The prognosis, or expected outcome, of CLL is based on many factors, including the stage of the disease, the age of the patient, and their overall health.2 Over the past few decades, the survival rate for leukemia, including CLL, has been steadily increasing. (Survival rates are based on previous outcomes of people who survive a set amount of time after diagnosis. In cancer estimates, experts use the “five-year survival rate” as a marker. However, it is important to keep in mind that many people live beyond five years after diagnosis and the statistics are not necessarily predictive for any one individual.) Based on data from 2008-2014, the National Cancer Institute has determined the five-year survival rate for CLL is 84.2%.8

Written by: Emily Downward | Last reviewed: February 2019
  1. American Cancer Society. Available at Accessed 12/7/17.
  2. Leukemia & Lymphoma Society. Available at Accessed 12/7/17.
  3. American Red Cross. Available at Accessed 9/19/17.
  4. American Society of Hematology. Available at Accessed 9/19/17.
  5. Chronic lymphocytic leukemia, Available at Accessed 12/7/17.
  6. B-cell prolymphocytic leukemia and hairy cell leukemia, Available at Accessed 12/7/17.
  7. Chronic T-cell lymphocytic leukemia, Available at Accessed 12/7/17.
  8. SEER (Surveillance, Epidemiology and End Results) Cancer Statistics Review, National Cancer Institute. Available at Accessed 2/7/19.