Chronic Lymphocytic Leukemia (CLL) is a type of cancer that starts from white blood cells called lymphocytes in the bone marrow. It is the most common form of leukemia in adults. The term "chronic" in CLL comes from the fact that this leukemia typically progresses more slowly than other types of leukemia. The term "lymphocytic" in chronic lymphocytic leukemia comes from the cells affected by the disease, which are a group of white blood cells called lymphocytes that help the body fight infection. CLL mainly affects older adults.

CLL starts when healthy white blood cells (lymphocytes) in the bone marrow mutate or change into cancerous cells that multiply and crowd out healthy blood cells and platelets. The cancer cells start in the bone marrow but then go into the blood and can spread to other parts of the body, including the lymph nodes, liver, and spleen. In CLL, the leukemia cells often build up slowly, and many people dont have any symptoms for at least a few years. But over time, the cells grow and spread to other parts of the body.

Doctors arent certain what starts the process that causes chronic lymphocytic leukemia. Whats known is that something happens to cause changes (mutations) in the DNA of blood-producing cells. A cells DNA contains the instructions that tell the cell what to do. The changes tell the blood cells to produce abnormal, ineffective lymphocytes.

CLL may cause complications such as anemia, thrombocytopenia, and an increased risk of other cancers. Treatment options for CLL include chemotherapy, targeted therapy drugs, monoclonal antibodies, and stem cell transplant.