What is chronic lymphocytic leukemia (CLL)?

Leukemia is a cancer that starts in blood stem cells (immature blood cells) in the bone marrow. Bone marrow is the soft, spongy material that fills the centre of most bones. Blood cells are made in the bone marrow. Blood stem cells develop into either lymphoid stem cells or myeloid stem cells.

Lymphoid stem cells develop into lymphocytes. Lymphocytes are a type of white blood cell. They are usually found in blood and different parts of the lymphatic system, such as the lymph nodes and the spleen. Lymphocytes make antibodies to help fight infection.

Lymphocytic leukemia develops when too many blood stem cells in the bone marrow develop into abnormal lymphocytes. These abnormal lymphocytes are called leukemia cells, and they don’t work like healthy lymphocytes. As more leukemia cells build up in the bone marrow and blood, they crowd out healthy white blood cells, red blood cells and platelets.

Chronic lymphocytic leukemia (CLL) is a type of leukemia that develops slowly, over months or years.