Oxygen radicals, DNA base modifications, and aberrant SOD and CATALASE expression contribute to the progression of chronic lymphocytic leukemia (CLL), acute lymphoplastic leukemia, monoclonal B lymphocytosis (MBL), a disease marked by B-cell expansion, and the CLL phenotype, which characteristically show increased levels of 8-oxo-2′-deoxyguanosine (8-oxo-dG) in lymphocytes and in urine. The gene discussed is SOD1; the disease is B-cell chronic lymphocytic leukemia.