leukemia fever :: Article Creator What Is Chronic Lymphocytic Leukemia? 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 something happens to change the genetic code inside your cells that make white blood cells. Normally, these cells help your body fight infection, but because of the change-- called a mutation-- faulty white blood cells that don't work like they should are made instead. These damaged blood cells build up in your bone marrow, crowding out healthy cells, and keeping new blood cells from being made. As they continue to grow, they can spread to your blood and build up in your organs. CLL gets worse slowly, and many people don't have symptoms at first. Over time, you could have swollen lymph nodes, a fever, a tired feeling, belly pain, night sweats, weight loss, or more freque...