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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 spreads to the blood. CLL may also be called chronic lymphoid leukemia. CLL is a blood cancer that begins in lymphoid cells, which can become B cells, T cells, and natural killer cells.1,2

Most forms of CLL grow slowly, with the cancerous cells accumulating over a long time. Many people do not have symptoms until the cancerous cells spread to the lymph nodes, liver, or spleen. However, CLL can be more difficult to treat than acute leukemias.1

How does chronic lymphocytic leukemia develop?

The cells that make up the blood (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 in bones. The bone marrow contains blood stem cells, which are immature cells that can become different types of cells in the body. The cells convert 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. There are two main kinds of CLL:

  • B-cell CLL
  • T-cell CLL5

More than 95 percent of people who have CLL have the B-cell type. About 1 percent of people with B-cell type have a subtype called B-cell prolymphocytic leukemia (PLL). Another B-cell CLL is called hairy cell leukemia.5,6

T-cell CLL is much less common. Subtypes of T-cell CLL include:

  • Large granular lymphocytic leukemia
  • T-cell prolymphocytic leukemia
  • Adult T-cell leukemia/lymphoma
  • Sezary syndrome (a form of T-cell lymphoma)5

Some forms of CLL grow slowly and may remain stable for years. Other types grow quickly. Making treatment more difficult, the same type of CLL may behave differently from person to person.2,5

Who gets chronic lymphocytic leukemia (CLL)?

CLL is the most common type of leukemia in adults over age 19. About 90 percent of people diagnosed with CLL are over age 50. CLL rarely occurs in people younger than 40, and it occurs extremely rarely in children.1-8

What are the risk factors for 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
  • Over age 50
  • Being male (the risk is slightly higher in males than females)
  • Being from North America or Europe1

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

CLL may be diagnosed before the person notices any symptoms, often blood tests are performed for other reasons. Symptoms that do occur may be vague or easily mistaken as being caused by another illness. Common CLL symptoms include

How is chronic lymphocytic leukemia staged (CLL)?

Staging describes where a cancer is located, how much it has spread and where. CLL is described as Stage 0, I, II, III, or IV. Each stage may also be rated low risk, intermediate risk, and high risk. Together, this information is used to decide how best to treat the cancer.1,2,5

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

The outcome of CLL is based on many factors, including:

  • Stage of the disease
  • Age of the patient
  • Overall health of the patient2

Based on data from 2009-2015, the National Cancer Institute has found the 5-year survival rate for CLL is 85.1 percent.8

Over the past few decades, the survival rate for all leukemias, including CLL, has steadily increased. Survival rates are based on the outcomes of earlier people who survive a certain amount of time after diagnosis. In cancer estimates, experts use the “5-year survival rate” as a marker. It is important to remember that many people live well past 5 years after diagnosis. Every case is different.

Written by: Emily Downward & Jessica Johns Pool | Last reviewed: November 2019
  1. American Cancer Society. Available at: https://www.cancer.org/. Accessed 12/7/17.
  2. Leukemia & Lymphoma Society. Available at: http://www.lls.org/leukemia/chronic-lymphocytic-leukemia/. Accessed 11/21/19.
  3. American Red Cross. Available at: http://www.redcrossblood.org/learn-about-blood/blood-components. Accessed 9/19/17.
  4. American Society of Hematology. Available at: http://www.hematology.org/Patients/Basics/. Accessed 9/19/17.
  5. Cancer.net. Leukemia - Chronic Lymphocytic - CLL: Introduction. Available at: https://www.cancer.net/cancer-types/leukemia-chronic-lymphocytic-cll/introduction. Accessed 11/21/19.
  6. B-cell prolymphocytic leukemia and hairy cell leukemia, Cancer.net. Available at: https://www.cancer.net/cancer-types/leukemia-b-cell-prolymphocytic-leukemia-and-hairy-cell-leukemia/introduction. Accessed 12/7/17.
  7. Chronic T-cell lymphocytic leukemia, Cancer.net. Available at: https://www.cancer.net/cancer-types/leukemia-chronic-t-cell-lymphocytic/introduction. Accessed 12/7/17.
  8. SEER (Surveillance, Epidemiology and End Results) Cancer Statistics Review, National Cancer Institute. Available at: https://seer.cancer.gov/statfacts/html/clyl.html. Accessed 11/21/19.