Statistics

Statistics

Estimated new cases and deaths from chronic lymphocytic leukemia (CLL) in the United States in 2008:[1]

• New cases: 15,110.
• Deaths: 4,390.

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.[5] At the present time, the natural history or clinical significance of these findings is unknown. In a selected series of 185 patients followed prospectively for a median of 6.7 years, progressive lymphocytosis occurred in 28% of patients, progressive CLL occurred in 15% of patients, and chemotherapy was required in 7% of patients.[4]

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.[6-10] Antileukemic therapy is frequently unnecessary in uncomplicated early disease.[11] The median survival for all patients ranges from 8 to 12 years in older trials with data from the 1970s through the 1990s.[11,12] 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.[13]

As found in one report, CLL occurs primarily in middle-aged and elderly adults, with increasing frequency in successive decades of life.[14] 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.[15] Immunological aberrations, including Coombs-positive hemolytic anemia, immune thrombocytopenia, and depressed immunoglobulin levels may all complicate the management of CLL.[16] Prognostic factors that may help predict clinical outcome include cytogenetic subgroup, immunoglobulin mutational status, ZAP-70, and CD38 (see Prognostic Factors).[2,17-25] 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.[26]

Confusion with other diseases may be avoided by determination of cell surface markers. CLL lymphocytes coexpress the B-cell antigens CD19 and CD20 along with the T-cell antigen CD5.[27] This coexpression only occurs in one other disease entity, mantle cell lymphoma. CLL B cells express relatively low levels of surface-membrane immunoglobulin (compared with normal peripheral blood B cells) and a single light chain (kappa or lambda).[11] CLL is diagnosed by an absolute increase in lymphocytosis and/or bone marrow infiltration coupled with the characteristic features of morphology and immunophenotype, which confirm the characteristic clonal population.

The differential diagnosis must exclude hairy cell leukemia (refer to the PDQ summary on Hairy Cell Leukemia Treatment for more information), and Waldenström macroglobulinemia (refer to the PDQ summary on Adult Non-Hodgkin’s Lymphoma Treatment for more information). Waldenström macroglobulinemia has a natural history and therapeutic options similar to CLL, with the exception of hyperviscosity syndrome associated with macroglobulinemia as a result of elevated immunoglobulin M. Prolymphocytic leukemia (PLL) is a rare entity characterized by excessive prolymphocytes in the blood with a typical phenotype that is positive for CD19, CD20, and surface-membrane immunoglobulin and negative for CD5. These patients demonstrate splenomegaly and poor response to low-dose or high-dose chemotherapy.[11,28] Cladribine (2-chlorodeoxyadenosine) appears to be an active agent (60% complete remission rate) for patients with de novo B-cell prolymphocytic leukemia.[29][Level of evidence: 3iiiDiv] Alemtuzumab (campath-1H), an anti-CD52 humanized monoclonal antibody, has been used for 76 patients with T-cell prolymphocytic leukemia after failure of prior chemotherapy (usually pentostatin or cladribine) with a 51% response rate (95% confidence interval, 40%–63%) and median time to progression of 4.5 months (range, 0.1–45.4 months).[30][Level of evidence: 3iiiDiv] These response rates have been confirmed by other investigators.[31] Patients with CLL who show prolymphocytoid transformation maintain the classic CLL phenotype and have a worse prognosis than PLL patients. Large granular lymphocytic leukemia is characterized by lymphocytosis with a natural killer cell immunophenotype (CD2, CD16, and CD56) or a T-cell immunophenotype (CD2, CD3, and CD8).[32,33] These patients often have neutropenia and a history of rheumatoid arthritis. The natural history is indolent, often marked by anemia and splenomegaly. This condition appears to fit into the clinical spectrum of Felty syndrome.[34] Therapy includes steroids, low doses of oral cyclophosphamide or methotrexate, and treatment of the bacterial infections acquired during severe neutropenia.[32,35,36]

References

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