The impact of molecular cytogenetics on chronic lymphoid leukaemia.

Chronic lymphoid leukaemias are clonal expansions of B and T cells with mature membrane phenotype. Cytogenetic study of these cases usually requires mitogenic stimulation and can often be hindered by a lack of response of the tumour cells to mitogen, poor quality metaphases, complex markers and proliferation of normal cells. In situ hybridisation with fluorescence-labelled chromosome-specific centromeric DNA probe, single or low copy sequences and whole chromosome paints which hybridise to complementary sequences allow the detection of numerical and structural abnormalities on metaphase and interphase cells with much greater efficiency. Comparative genomic hybridisation uses whole genomic tumour DNA as probe which is hybridised to normal metaphases. It is particularly useful for detecting chromosomal changes without being dependent on the dividing tumour cells. The application of these techniques to the investigation of chronic lymphoid leukaemias is reviewed with emphasis on the work done in our laboratory on trisomy 12 and the tumour suppressor region 13q14 in chronic lymphocytic leukaemia, translocation t(11;14) (q13;q32) in mantle cell lymphoma and other chronic B cell leukaemias, inv(14) (q11q32), i(8q) and complex markers in T prolymphocytic leukaemia.