Prognostic Significance Of Copy Number Alterations In B-Lineage Adult Acute Lymphoblastic Leukemia Patients Enrolled In Risk-Adapted Protocols From The Pethema Group

In the last years genome wide profilings have identified recurrent Copy Number Alterations (CNA) in genes potentially involved in the pathogenesis of Acute Lymphoblastic Leukemia (ALL). These studies have identified deletions in B-cell development genes (IKZF1, EBF1, PAX5, TCF3, etc.), cell cycle regulation genes (CDKN2A/B, RB1, TP53, etc.), glucocorticoid resistance genes (BTG1, CREBBP) and growth factor receptors genes (CRLF2, CSF2RA, IL3RA) among others. Some of these CNA (i.e. IKZF1, CDKN2A, CRLF2) have been reported to have prognostic significance in several pediatric series but there are very few data regarding their impact in B-lineage adult ALL. Our aim was to analyze the frequency and prognostic significance of CNA in a series of 125 B-lineage adult ALL patients treated according to risk-adapted protocols from the Spanish PETHEMA Group.

Bone marrow or peripheral blood (with significant blast burden) samples from 125 B-lineage adult ALL patients enrolled in risk-adapted protocols from the PETHEMA Group were analyzed at diagnosis. MLPA assays (MRC-Holland) were performed for the following genes: IKZF1, IKZF2, IKZF3, EBF1, CDKN2A/B, PAX5, ETV6, BTG1, RB1, hsa-miR-31, X/Y PAR1 region genes (CRLF2, CSF2RA, IL3RA) and 14q32.33 region genes (IGH D, MTA1, KIAA0284). Fragment analysis was made by Genescan in an ABI-3130 sequencer (Applied Biosystems). Data normalization provided a value indicative of the presence or absence of CNA: 0-0.20 homozygous deletion, 0.21-0.70 heterozygous deletion, 0.71-1.30 normal, 1.31-1.70 heterozygous duplication and 1.71-2.20 homozygous duplication.

The median age [range] was 40 [15-74] years, 71 (57%) males, median WBC count 12.11 x10⁹/L [0.4-388]. Immunophenotype: pro-B 14 (11%), common 71 (58%), pre-B 26 (21%), mature-B 10 (8%), unavailable 2 (2%). Cytogenetics: normal 16 (13%), hyperdiploid 6 (5%), hypodiploid 2 (2%), t(9:22) 20 (16%), t(1;19) 8 (6%), 11q23/MLL 11 (9%), 8q24/C-MYC 7 (5%), complex 1 (1%), iAMP21 2 (2%), other translocations or deletions 31 (25%), no growth 20 (16%). CNA frequencies of the 125 patients are shown in the table.

IKZF1 deletions were significantly associated with EBF1 deletions, high WBC count and Philadelphia (Ph) chromosome. In the IKZF1 deleted cohort whole gene deletions were as frequent as Ik6 isoforms (28% each). A high codeletion rate was detected in genes located in 9p (CDKN2A/B with PAX5, CDKN2A/B with hsa-miR-31 and PAX5 with hsa-miR-31). CDKN2A/B also showed concomitant deletions with ETV6 while PAX5 showed codeletions with BTG1. CDKN2A/B and PAX5 deleted patients had higher WBC counts than non-deleted individuals.

Clinical follow-up data was available for 123 patients of the whole series and for the 105 patients of the Ph-negative cohort. Multivariate analysis showed that advanced age, BTG1 deletions and EBF1 deletions were negative prognostic factors for achieving Complete Remission (CR) and WBC count and IKZF1 deletions significantly reduced CR duration in both cohorts. Interestingly, there were significant differences in relapse rates between whole and partial gene IKZF1 deletions. IKZF1 haploinsufficient patients had a probability of CR duration at 3 years of 83% ± 30% vs. 6% ± 12% of partial gene deletion carriers. Advanced age and IKZF1 deletions were predictors for overall survival in the Ph-negative cohort and age>30 years, IKZF1 deletions and hsa-miR-31 deletions were associated with poor prognosis in the whole series.

In B-lineage adult ALL, deletions of IKZF1, EBF1, BTG1 or hsa-miR-31 are markers with prognostic significance in addition to age and WBC count. Patients with partial IKZF1 gene deletions have a significantly higher probability of relapse than those with whole gene loss. These genetic abnormalities could help to better define prognostic subgroups in adult patients with B-lineage ALL.

Supported by the grants PI10/01417 and RD12-0036-0029 from Instituto Carlos III and a grant from the Spanish Society of Hematology and Hemotherapy (2012).

No relevant conflicts of interest to declare.