Note: Estimated new cases and deaths from chronic lymphocytic leukemia (CLL) in the United States in 2007:[1]

• New cases: 15,340.
• Deaths: 4,500.

Note: Some citations in the text of this section are followed by a level of evidence. The PDQ editorial boards use a formal ranking system to help the reader judge the strength of evidence linked to the reported results of a therapeutic strategy. (Refer to the PDQ summary on Levels of Evidence for more information.)

CLL is a disorder of morphologically mature but immunologically less mature lymphocytes and is manifested by progressive accumulation of these cells in the blood, bone marrow, and lymphatic tissues.[2] In this disorder, lymphocyte counts in the blood are usually greater than or equal to 5,000/mm³ with a characteristic immunophenotype (CD5 and CD23 positive B cells).[3] As assays have become more sensitive for detecting monoclonal B-CLL–like cells in peripheral blood, researchers have detected a monoclonal lymphocytosis of undetermined significance (MLUS) (i.e., MLUS in analogy to the monoclonal gammopathy of undetermined significance, MGUS) in 3% of adults older than 40 years and 6% in adults older than 60 years.[4] Such early detection and diagnosis may falsely suggest improved survival for the group and may unnecessarily worry or result in therapy for some patients who would have remained undiagnosed in their lifetime, a circumstance known in the literature as overdiagnosis or pseudodisease. At the present time, the natural history or clinical significance of these findings is unknown.

For patients with progressing CLL, treatment with conventional doses of chemotherapy is not curative; selected patients treated with allogeneic stem cell transplantation have achieved prolonged disease-free survival.[5,6,7,8,9] Antileukemic therapy is frequently unnecessary in uncomplicated early disease.[10] The median survival for all patients ranges from 8 to 12 years in older trials with data from the 1970s through the 1990s.[10,11] There is, however, a large variation in survival among individual patients, ranging from several months to a normal life expectancy. Treatment must be individualized based on the clinical behavior of the disease.[12]

CLL occurs primarily in middle-aged and elderly adults, with increasing frequency in successive decades of life.[13] The clinical course of this disease progresses from an indolent lymphocytosis without other evident disease to one of generalized lymphatic enlargement with concomitant pancytopenia. Complications of pancytopenia, including hemorrhage and infection, represent a major cause of death in these patients.[14] Immunological aberrations, including Coombs-positive hemolytic anemia, immune thrombocytopenia, and depressed immunoglobulin levels may all complicate the management of CLL.[15] Prognostic factors that may help predict clinical outcome include cytogenetic subgroup, immunoglobulin mutational status, ZAP-70, and CD38 (see Prognostic Factors).[2,16,17,18,19,20,21,22,23,24] Patients who develop an aggressive high-grade non-Hodgkin lymphoma, usually diffuse large B-cell lymphoma and termed a Richter transformation, have a poor prognosis.[25]