Chronic lymphocytic leukemia (CLL) / Small lymphocytic lymphoma (SLL)
CLL is classified by the accumulation and rapid reproduction of clonal B cells in the blood, bone marrow, and lymph nodes. CLL and SLL are essentially the same disease, the only difference being where the cancer primarily occurs. When most of the cancer cells are located in the bloodstream and the bone marrow, the disease is referred to as CLL, although the lymph nodes and spleen are often involved. When the cancer cells are located mostly in the lymph nodes, the disease is called SLL.
The progression of CLL is extremely variable ranging from indolent (slow-growing) disease not requiring treatment to one that progresses rapidly and is resistant to treatment. CLL is one of the most common types of leukemia in adults, usually occurring during or after middle age. It rarely occurs in children.