Chronic Lymphocytic Leukemia (CLL) is the monoclonal proliferation of malignant B lymphocytes. It is the most common adult leukemia in Western countries, accounting for 30% of all cases in the United States. CLL typically affects adults greater than 65 years of age. A key laboratory abnormality found in CLL is lymphocytosis. Smudge cells (fragile cells that break on the slide during processing) are common on peripheral blood smear. Approximately 5% of cases transform to a diffuse large B-cell lymphoma, a process called a Richter transformation.