Chronic lymphocytic leukemia (CLL) is the most common form of leukemia in adults. It starts in the bone marrow in the cells that will become white blood cells. It takes time for leukemia cells to build up in the body, and some people live with this form of cancer for years with few or no symptoms. Once there are enough leukemia cells, however, they can spread to your lymph nodes, liver, and spleen. At that point, you will develop symptoms and require treatment.