Chronic lymphocytic leukemia (CLL) and its lymphoma variant, small lymphocytic lymphoma (SLL) were for decades considered diseases caused by the progressive accumulation of abnormal lymphocytes. The prevailing view being that CLL and SLL disease processes were driven by an underlying defect in apoptosis. While resistance to apoptosis appears to be important in the CLL and SLL disease process, recent studies suggest that cellular proliferation is more important than previously realized.