B-cell chronic lymphocytic leukemia (CLL), the most frequent leukemia in the Western world, is characterized by extremely variable clinical courses with survivals ranging from 2 to 20 years. The pathogenetic factors playing a key role in defining the biological features of CLL cells, hence eventually influencing the clinical aggressiveness of the disease, can be divided into “intrinsic factors,” mainly genomic alterations of CLL cells, and “extrinsic factors,” responsible for micro-environmental interactions of CLL cells; this latter group includes interactions of CLL cells occurring via the surface B-cell receptor (BCR) and dependent on specific molecular features of the BCR itself and/or on the presence of the BCR-associated molecule ZAP-70, or via other non-BCR-dependent interactions, e.g. specific receptor–ligand interactions, such as CD38–CD31 or CD49d–VCAM.
It is a common notion that, differently from other B-cell lymphoid neoplasms, CLL is characterized by recurrent DNA gains and losses, and not by the presence of specific chromosomal translocations. However, using improved protocols to obtain informative metaphases (1,2) or microarray-based comparative genomic hybridization (3), chromosomal abnormalities can now be shown in over 90% of patients (2). Only 20% of the events are balanced translocations, whilst the vast majority of them are unbalanced translocations, determining losses or gains of genomic material (1,2). Specific genomic events are associated with a different clinical outcome, and, not surprisingly, the frequency of specific genomic events varies between CLL bearing mutated (M) and unmutated (UM) immunoglobulin heavy-chain variable (IGHV) genes (see below for IGHV molecular features). The recurrent chromosomal aberrations are summarized in Table 72.1.