... outcome in CLL [2-8]. In the present review, the main factors playing a role in defining the biological features of CLL cells, hence eventu-ally influencing the clinical aggressiveness of the disease,are ... occurring during B celldifferentiation is the so-called class-switch recombination(CSR), which modify the constant region of heavy chains,thus altering the effector functions of IG [66]. The ... chromosomal aberra-tions are summarized in Table 1.13q14.3 deletion The most common lesion in CLL is chromosome 13q14.3deletion, occurring in half of the cases [4]. The deletion isoften interstitial...