Chronic lymphocytic leukemia (CLL) a B lymphocyte (rarely T lymphocytes) clonal malignancy. The disease is usually indolent, with slowly progressive accumulation of long-lived small lymphocytes. These cells are immunoincompetent and respond poorly to antigenic stimulation.

Chronic lymphocytic leukemia is manifested clinically by immunosuppression, bone marrow failure, and organ infiltration with lymphocytes. Immunosuppression, bone marrow failure, and infiltration of organs account for most clinical manifestations. Immunodeficiency is also related to inadequate antibody production by the abnormal B cells. With advanced disease, chronic lymphocytic leukemia may cause damage by direct tissue infiltration.