In CLL with Complex Aberrant Karyotype Distinct Entities Can Be Deciphered by Molecular Genetic and Cytogenetic Parameters

Metaphase cytogenetics have recently defined important prognostic subgroups in CLL. In addition to the poor prognosis FISH markers del(17p) and del(11q), the presence of translocations and a complex aberrant karyotype, defined by chromosome banding analyses, have been associated with shorter overall survival in a retrospective analysis. Thus far, a complex aberrant karyotype is defined by a number of three or more chromosomal aberrations, therefore, we aimed at characterizing an unselected CLL cohort of 92 patients with complex aberrant karyotype in more detail with molecular genetic, cytogenetic, and immunophenotypic parameters. Median age at diagnosis was 62.5 years (range: 33.4–83.3 years), the male/female ratio was 2.8. An unmutated IgVH status (<= 2% mutations) was detected in 51 (60.7%) of 84 analyzed samples. A positive CD38 expression (>= 30% CD38 positive cells) was detected in 55 (64%) of 86 samples and TP53 gene mutations by denaturing high performance liquid chromatography of exons 4–9 of TP53 in 29 (36.7%) of 79 samples. As the main approach for prognostication in CLL uses FISH for del(17p), del(11q), +12, del(13q) sole and normal, we related our cohort with complex aberrant karyotype into these different FISH categories. The poor prognosis markers del(17p) and del(11q) were detected with frequencies of 39.1% (n=36) and 22.8% (n=21), respectively, accounting for almost two third of all samples (n=57, 61.9%). An overlap between del(17p) and del(11q) was detected in 5 of the 36 del(17p) cases. The intermediate risk FISH marker +12 and low risk FISH markers del(13q) as sole abnormality and “normal karyotype” appeared with an incidence of 8.7% (n=8), 21.7% (n=20) and 7.6% (n=7), respectively. The high incidence of del(11q) and del(17p) in complex karyotype seems likely, as genes implicated in sensing DNA damage and in regulating apoptosis, ATM and TP53, are candidate genes in these deleted regions. As TP53 mutations have been suggested as independent poor prognostic markers, we also added TP53 gene mutation analysis to the FISH stratification. Del(17p) was associated with TP53 mutation in 26 (86.7%) of 30 analyzed cases, whereas the three residual TP53 mutations were associated with del(11q) (n=1) and del(13q) as sole abnormality (n=2). Therefore, we chose to merge samples with high risk features within the complex karyotype into one group (n=59), i.e., samples with del(17p), del(11q) or TP53 mutation, and compared these samples to the remaining samples (n=33). Effectively, the high risk group compared to the other cohort was significantly associated with an unmutated IgVH (p=0.02, Fisher’s exact test) and with an increased, median amount of cytogenetic aberrations (4.9 vs. 3.7 aberrations, p=0.005, t-test). However, no significant difference between the two groups regarding a CD38 positive status was detected (p=0.257).

The prognostic impact of high risk features (del(17p), del(11q) and TP53 mutation) within the group defined above vs the lower risk group was analyzed with log-rank statistics with respect to time from diagnosis of CLL to initial treatment (TTT). 34 patients from the high risk group and 18 patients from the low risk group were available for analysis. The high risk features within the complex karyotype were significantly associated with a higher risk of early treatment in log-rank statistics with a median TTT of 12.2 month in the higher risk group compared to 70.1 month in the lower risk group (p=0.005). In conclusion, based on poor risk cytogenetic and molecular genetic features within the group of CLL with complex aberrant karyotype, we characterized patients with a higher risk of early treatment initiation. This group includes samples with del(17p), del(11q) and TP53 mutations.