High Incidence of Translocations in CLL: A New Prognostic Marker for Infavorable Survival Outcome.

BACKGROUND: Conventional metaphase cytogenetics underestimates the frequency of specific chromosome aberrations in B-CLL due to the low in vitro proliferative activity of CLL cells. We could recently show that stimulation of CLL cells with CD40 ligand (CD40L) induced cell cycle progression and increased the frequency of metaphases of CLL cells, which are then suitable for chromosome banding. In the present study we compared this new technique, CD40L-enhanced cytogenetics (CEC) with molecularcytogenetic data obtained by fluorescence in situ hybridization (FISH) on CLL cells.

Methods: Blood samples were obtained from 95 CLL patients (Binet A: 31%, Binet B: 30%, Binet C: 39%) and subjected to simultaneous analysis by CEC and FISH. 56% of patients were previously untreated, while 44% of patients received at least one course of chemotherapy prior to the study.

RESULTS: By FISH, 80% of analysed samples revealed aberrations like deletion of chromosome 11, 13 or 17 or trisomy 12. By CEC, chromosomal aberrations (range 0 to 14; median: 1) were detected in 90% of samples involving all chromosomes except the X chromosome. Importantly, a high incidence of balanced and unbalanced translocations were seen in 33 patients (35%) while 70% of the breakpoints involved were recurring. Median treatment-free survival (TFS) was significantly shorter for patients with translocations P< .0001). For patients with unbalanced translocations, overall survival was also significantly (decreased P= .0007). 25% of patients with 13q deletion as single aberration in FISH analysis additionally showed translocations (by CEC. These patients had a significantly shorter TFS compared to patients with 13q deletion as true sole aberration (median TFS: 36 mo vs. 132 mo; P= .0004). This was also true for patients with deletion of 11q. Patients with 11q- and translocations had a significant shorter TFS than patients with 11q- without translocations (median TFS: 13 mo vs. 48 mo; P= .011). All patients with 17p deletion showed translocations. In order to exclude the possibility that cytogenetic aberrations occurred as a possible treatment-associated secondary event, in a second analysis only patients who were untreated at the time of cytogenetic analysis were evaluated. In 22% of untreated patients translocations were detected and again they showed significantly lower TFS rates compared to patients without translocations (median TFS: 26 mo vs. 109 mo; P = .0128). In a multivariate analysis including Binet stage, presence of a complex karyotype (≥ 3 chromosomal aberrations), CD38 expression, 11q- and 17p-, the occurance of translocations proved to be the prognostic marker with the highest impact for an infavorable clinical outcome P< .001).

CONCLUSION: Taken together, CEC is able to detect new chromosomal aberrations in CLL and enables a risk assessment for CLL patients based on the incidence of translocations otherwise indetectable by FISH or conventional metaphase cytogenetics.