CLL comprises about 30% of all leukemias. It is uncommon in Asians. The lymphocytes of CLL are B-lymphocytes, although there are about 2%-3% (range, 2%-5%) of cases that consist of T-lymphocytes. The disease is usually found after the age of 50. It is twice as common in men than in women. Average survival is 3-7 years after diagnosis, with an appreciable number of patients alive at 8-10 years. Various chromosome abnormalities are reported in about 50% of patients. Total WBC counts are usually elevated; in one study about 10% were normal; about 45% were between 10,000 and 50,000/mm3 (10-50 Ч 109/L), about 15% were between 50,000 and 100,000/mm3, and about 35% were more than 100,000/mm3. The majority (frequently, the great majority) of the WBCs are lymphocytes; of these, most (often nearly all) are mature types. In some patients there may be a considerable number of prolymphocytes and even some blasts, but this is not common. There is mild to moderate normocytic-normochromic anemia, usually without reticulocytosis. Platelets are decreased in approximately 40% of cases, but this may not occur until late in the disease. The bone marrow contains at least 20% lymphocytes and usually more than 50%. There is splenomegaly in 65%-75% of cases, usually to at least moderate degree, and moderate adenopathy in 65%-85% of cases. Hepatomegaly is found in approximately 50% of patients. Occasionally the splenomegaly and adenopathy are marked. There is a considerable tendency to infection, and this is often the cause of death. A Coombs’-positive autoimmune hemolytic anemia is reported in about 10% (5%-20%) of cases; a Coombs’-negative hemolytic anemia, often without a reticulocytosis, eventually develops in 15%-25% of cases. About 50% (40%-77%) of patients eventually develop some degree of hypogammaglobulinemia, with any or all of the major immunoglobulins (IgG, IgA, and IgM) being involved. There is some disagreement as to which of the three is most frequently decreased. Up to 5% of CLL patients develop a serum monoclonal protein like those produced in myeloma.

In the majority of patients with CLL the disease is relatively benign and only slowly progressive over a period of several years. In approximately 20% the disease is more aggressive. Whether this represents a distinct subset of CLL or simply diagnosis relatively late in the course of the disease is still being debated. Patients with CLL have an increased chance of developing a second malignancy, most often a carcinoma. This tendency is disputed by some but has been reported to be as high as 34%. One well-recognized condition is called Richter’s syndrome, in which approximately 5% (literature range, 3%-15%) of CLL cases evolve into or develop non-Hodgkin’s lymphoma, most commonly the large cell type (histiocytic lymphoma in the Rappaport classification). About 1.5% (0%-6.9%) of CLL cases terminate in a “blast crisis.” The majority are ALL, but acute myeloblastic leukemia (AML) and others have been reported. Finally, a few patients with CLL develop transformation to prolymphocytic leukemia, which is more aggressive. Prolymphocytic leukemia can also exist without known previous CLL but is very uncommon.