IBTK and B-cell chronic lymphocytic leukemia: A different methylation pattern of the IBTK gene is reported in poor-prognostic Immunoglobulin Heavy Variable Chain (IGHV)-unmutated Chronic Lymphocytic Leukemia (U-CLL) compared with favorable prognostic IGHV-mutated CLL (M-CLL)8, suggesting that the altered IBTK expression could be associated with tumor progression and aggressiveness.