What Is Chronic Lymphocytic Leukemia? Chronic lymphocytic leukemia (CLL) is a cancer that affects a type of white blood cell called lymphocytes. Lymphocytes help your body fight infection.

Chronic lymphocytic leukemia-- or CLL-- is a type of cancer that happens in your blood and bone marrow, the spongy tissue inside your bones. While the exact cause isn't known, doctors do know that ...