Molecular cytogenetic investigations in chronic B-cell lymphoproliferative disorders: novel mitosis stimulators and clonal evolution

Cytogenetic studies in B-cell chronic lymphoproliferative disorders have been traditionally limited by the poor number of metaphases obtained in cell cultures: encouraging results are emerging from the introduction of novel mitogenic agents and are a field of particular interest. Furthermore, the availability of FISH (fluorescence in situ hybridization) technique and its applicability on interphase cells significantly improved our knowledge about cytogenetic aberrations occuring in this class of disorders, allowing us to better characterize crucial moments in the natural history of the disease, like, specifically, clonal evolution. To compare the efficiency of novel mitogenic agents versus traditional mitosis inductors, 18 patients with splenic marginal zone lymphoma (SMZL) were studied. Three cultures using oligodeoxynucleotide (ODN) plus interleukin-2 (IL-2), or TPA, or LPS were setup in each patient. Seventeen/18 cases with ODN + IL2 showed moderate/good proliferation (94,4%) as compared with 10/18 cases with TPA and LPS (55%) (P = .015); 14/18 (77, 7%) cases with ODN + IL2 had sufficient good quality of banding as compared with 8/18 cases (44, 4%) with TPA and LPS. The karyotype could be defined from ODN+ IL2-stimulated cultures in all 18 patients, 14 of whom (77,7%) had a cytogenetic aberration, whereas clonal aberrations could be documented in 9/18 and in 3/18 cases by stimulation with LPS and TPA, respectively. Recurrent chromosome aberrations in our series were represented by aberrations of chromosome 14q in 5 patients, by trisomy 12 and 7q deletion in 4 cases each, and by abnormalities involving 11q and 13q in two cases each. These findings show that stimulation with ODN + IL2 offers more mitotic figures of better quality and results in an increased rate of clonal aberrations in SMZL, making this method ideal for prospective studies aiming at the definition of the prognostic impact of cytogenetic aberrations in this disorder. Furthermore, to better define the significance of clonal evolution (CE) including 14q32 translocations involving the immunoglobulin heavy chain gene (IGH) in chronic lymphocytic leukemia (CLL), 105 patients were analyzed sequentially by fluorescence in situ hybridization (FISH) with the following panel of probes: 13q14/D13S25, 11q22/ATM, 17p13/TP53, #12- centromere and 14q32/IGH break-apart probe. CE was observed in 15/105 patients after 24-170 months (median 64). Recurring aberrations at CE were 14q32/IGH translocation in seven patients; other aberrations were 17p-, 11q-, biallelic 13q- and 14q32 deletion. CE was detected in 15/58 pretreated patients; in contrast, none of 47 untreated patients developed CE (p < 0.0001). In two cases the appearance of 14q32/IGH translocation was first detected in the bone marrow (BM) or in the lymph node (LN) and 13-58 months later in the peripheral blood (PB). ZAP70+ and high-risk cytogenetics predicted for the occurrence of CE with borderline statistical significance (p = 0.055 and 0.07, respectively). Shorter time to first treatment (TTT) and time to chemorefractoriness (TTCR) were noted in 15 patients with CE when compared to patients without CE (TTT: 35 vs. 71 months, p = 0.0033 and TTCR: 34 vs. 86 months, p = 0.0046, respectively). Survival after the development of CE was 32 months (standard error 8.5). We arrived at the following conclusions: (i) 14q32/IGH translocation may represent one of the most frequent aberrations acquired during the natural history of CLL and (ii) it may be detected earlier in BM or LN samples; (iii) CE including 14q32/IGH translocation occurs in pre-treated patients with short TTT and TTCR; (iii) survival after CE is relatively short.