With proper CLL cell culture and cytogenetic technique, clonal chromosome abnormalities are found in one-half of patients with CLL, and they indicate poor prognosis. In contrast to most hematological tumors, in which chromosomal abnormalities are mainly balanced structural abnormalities (translocations), the most common aberrations in CLL are unbalanced deletions with variable breakpoints involving chromosomes 13q, 11q, and 6q, as well as trisomy of chromosome 12. Of these, only +12 and del(13q) frequently occur as single abnormalities. The deletions may be small and require FISH analysis for detection. However, cytogenetic techniques are required for evaluating the entire genome and to assess complex karyotypes properly. No defined genetic event behind these aberrations has been identified. Cytogenetics as well as FISH analyses thus indicate surrogate genetic abnormalities than a true underlying genetic event of biological importance. Cytogenetic data indicate that complex karyotypes are associated with poor prognosis. p53 deletions, although rare, also indicate poor prognosis. The hierarchical model of genetic events detected by FISH proposes a poor prognosis for patients with deletions 11q22-q23, although these are mostly found in younger patients and are probably associated with complex karyotypes. 13q deletions are more common in the postgerminal type of CLL with mutated IgVH genes and are associated with a good overall survival.
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