B-cell chronic lymphocytic leukemia (CLL) is a subtype of mature peripheral B-cell neoplasms, characterized by the accumulation of circulating malignant lymphocytes that typically express cell surface markers CD5, CD20, and CD23. It is the most common type of leukemia in adults in Western Europe and in the US. The median age at diagnosis is 65-70 years, with a male to female ratio of 2:1. Initially, most patients present with asymptomatic lymphocytosis and do not need cytoreductive therapy. Patients with active disease are characterized by a lymphocyte doubling time of less than 6 months, or progressive, even massive lymphadenopathy, hepatosplenomegaly, anemia and thrombocytopenia. Constitutional symptoms such as fever, night sweats, unintended weight loss, and extreme fatigue are common in advanced disease and can significantly impact quality of life. CLL also causes relative immunosuppression that increases the risk of infections that are ultimately the major cause of death in this patient population. Median survival at diagnosis ranges from 5 to 20+ years depending on risk factors, but is only 6 to 14 months for patients with CLL refractory to available therapies.