Chronic lymphocytic leukemia (CLL) is caused by the abnormal progressive accumulation of functionally incompetent monoclonal B-lymphocytes in blood, bone marrow, lymph nodes and spleen. It is the most common adult leukemia in Western countries, accounting for about 30% of total leukaemias. Worldwide there are approximately 180,000 new cases every year. A main focus in CLL research involved the evaluation of genetic features related to somatic gene mutation or deletions that disrupt apoptosis and enhance tumor cell proliferation. The best characterized genes are TP53 (also known as p53) and ATM, for which mutations and/or deletions have been described that predict rapid disease progression, resistance to conventional therapies and poor survival.