Chronic Lymphocytic Leukemia

Chronic lymphocytic leukemia (CLL) is a type of cancer in which the bone marrow makes too many lymphocytes, a type of white blood cell. CLL is one of the most common types of leukemia in adults and often occurs during or after middle age.

Normally, the bone marrow makes blood stem cells that become mature blood cells over time. A blood stem cell may become a myeloid stem cell or a lymphoid stem cell. A lymphoid stem cell becomes a lymphoblast cell before maturing into one of three types of lymphocytes: B lymphocytes that make antibodies to help fight infection, T lymphocytes that help B lymphocytes make antibodies to fight infection, and natural killer cells that attack cancer cells and viruses.

In the case of CLL, too many blood stem cells become abnormal lymphocytes, also called leukemia cells, which are not well equipped to fight infections. As the number of leukemia cells increases in the blood and bone marrow, there is less room for healthy white blood cells, red blood cells, and platelets, which can lead to infection, anemia, and easy bleeding.

Approximately 23,690 people in the United States were estimated to be diagnosed with CLL in 2025, and 4,460 were estimated to die of the disease, according to estimates published by the National Cancer Institute.

Chronic Lymphocytic Leukemia Treatment (PDQ®)

Source: National Cancer Institute