Karyotypic and molecular abnormalities in chronic lymphocytic leukaemia.

Introduction B cell chronic lymphocytic leukaemia (B-CLL) is the commonest type of adult leukaemia in the western world, accounting for over 40% of all adult patients with leukaemia.' About 50% of patients present with early stage, often asymptomatic disease. The disease may remain stable or slowly progress but at least half of all patients die of a cause unrelated to CLL. Age, sex, Binet stage, and karyotype status have all been identified as important independent prognostic factors.2 3 Clonal karyotypic abnormalities have been detected in approximately 50% of all patients with a complex karyotype, a high percentage of abnormal metaphases, trisomy 12, and abnormalities of chromosome 14, which are all associated with a poor prognosis.' The molecular changes responsible for the development and progression of CLL have not been elucidated fully, but both karyotypic and molecular studies have been hampered by the inclusion of patients with prolymphocytic leukaemia (PLL), splenic lymphoma with villus lymphocytes (SLVL), hairy cell leukaemia, and non-Hodgkin's lymphoma (follicular and mantle cell) in leukaemic phase. Unfortunately, no single test is diagnostic of CLL and a combination of morphology and immunophenotyping is required. The situation is confused further by the recent observation that subtypes of CLL exist with atypical features (and often atypical behaviour!). The aim of this review is therefore to try to clarify what is known about the karyotypic and molecular abnormalities in both typical and atypical CLL and to suggest future studies which may shed further light on this complex disease.